Physics II Lab Final
What is the speed of light in Water and BK-7 glass?
n = c/v Water: v = c/n = (3x10^8 m/s)/(1.333) = 2.25x10^8 m/s BK-7 glass: v = c/n = (3x10^8 m/s)/(1.53) = 1.96x10^8 m/s
The difference between open-circuit voltage and closed circuit voltage is the IR-drop inside the power supply. True or False?
True, because there is a small drop on the inside.
b. what is the time constant of the circuit?
r = RC r = (600 ohms)(6uF) = 3.6x10^3 seconds
A light ray in air is incident on 0.025 m thick plastic block at an angle of 30°. As the light wave merges from the opposite side of the block parallel to its original path, how much is the light ray displaced from the original path?
𝑑 = 𝑊 𝑠𝑖𝑛(𝜃1−𝜃2)/ 𝑐𝑜𝑠𝜃2 First: n1 x sin1() = n2 x sin2 () (1.00xsin(30 deg))/(1.51) = 19.33 degrees Second: d = W sin(angle1-angle2)/cos angle 2 d = (0.025 m)(sin(30-19.33))/cos(19.33) = 0.0049 m displaced
If a wave generator outputs a wave at a known value of 22 Hz and an experimenter measures the wave'e frequency as 20.0 Hz, what is the percent error? a. 9.0% b. 9.1% c. 9.5% d. 10%
(22 Hz - 20 Hz)/(22 Hz) x100 = 9.1%
What three ways can you measure Ohm's law
-resistance -voltage drop -current
In the graph above, example how many periods of the wave are shown?
1.5 periods
What happens to the flow of current?
A current will flow in the resistor until the energy stored in the capacitor is dissipated in the resistor. Let us assume that at time t=0 we close the switch. At that time, the potential difference across the capacitor is:
What is an ammeter?
An ammeter measures the current that flows between its terminals. An ammeter is always placed in series with the circuit or circuit element where the current flow is of interest. Since the current in each element of a series circuit is the same, the current flow through the meter will be the same as the current flow to the element of interest. Never connect an ammeter in parallel unless you intend to measure the short circuit current of a circuit or circuit element and you have made sure that destructive current levels won't be reached. When using a non-auto-ranging meter, select the highest possible range and reduce the range as necessary until the desired level of accuracy is reached. Always start with a range higher than the expected value to prevent damage to the meter.
How can you accidentally short circuit a wire?
Directly connect the two terminals of a battery together with a wire. That is called "short-circuiting" the battery and is dangerous. Don't do!!!
A 10 mega ohm resistor is connected in series with a 5 μF capacitor and 12 V battery. The capacitor is initially uncharged. After a time equal to one time constant find: a. The charge on the capacitor
First find initial charge on capacitor before discharge - Q=CV Q = (5x10^-6 F)(12V) = 6x10^-5 C Second find final Q after discharge when t=RC(r) Q(t) = Qo(1-e^-t/RC) (6x10^-5 C)(1-e^-1) = 3.79x10^-5 C
What is a period in a oscilloscope?
Horizontal distance x Time base
What happens if the index of refraction is less than the first?
If the index of refraction of the second medium is less that the first, then the light ray will be bent away from the normal.
What happens when the light intersects the interface at an angle?
If the light intersects the interface at an angle, the direction of the light will also change if there is a difference in the indices of refraction. This bending of the beam of light is called refraction of light.
Magnetic field intensity
If you could isolate single north poles (have north monopoles), the intensity of the magnetic field at any point is the force per unit North Pole placed at that point
Index of refraction is what?
Indices of refraction for some common optical materials are given in Table 1. The index of refraction for vacuum, i.e. the absence of any material, is one, and for air, it is nearly equal to one, nair= 1.0003
What is Thermionic emission?
Is electrons that are emitted from a hot cathode
What is Electric deflection?
Is used to modify the potentials (volts) on the horizontal and vertical deflector which alters the path of the beam.
Does a voltmeter have high or low internal resistance compared to the portion of a circuit across which it measures?
It has high internal resistance
What is light?
Light is electromagnetic radiation with electric and magnetic components that oscillate with a frequency 𝑓 and vary periodically with a wavelength λ.
Is the force constant along a magnetic field line?
No
Magnetism is everywhere, it arises from electron spin and orbit. Are most materials magnetized?
No, Most materials are not magnetic because all the atomic magnetic effects cancel each other out.
What is the equation for percent difference?
Percent difference: Percent difference is used when you are comparing your result to another experimental result. It is the absolute value of the difference of the values divided by their average, and written as a percentage.
Rapidly changing voltage is referred to as AC (alternating current) - what is AC?
Rapidly changing voltage is referred to as AC or alternating current. AC is the electric current that periodically reverses direction.
How does the wheatstone bridge work?
The Wheatstone bridge uses a zero or current null-comparison method to measure unknown resistance values by comparing them with resistance standards.
What does the current do?
The current (I) measures the flow of electrons through a circuit loop.
How does the current in the circuit flow?
The current that flows through most substances is directly proportional to the voltage, V applied to it.
State the physical properties that govern a wire's resistance?
The physical properties that effect the resistance of a wire are: -Temperature -Length -Material (resistivity) -Cross sectional area/width of wire
What is Ohm's Law?
The term Ohm's law refers to one of the fundamental relationships found in electronic circuits: that, for a given resistance, current is directly proportional to voltage. In this formula, V stands for voltage (in volts), I stands for current (in amperes), and R stands for resistance (in ohms)
What are ferromagnetic materials?
These are materials that have the capability of being magnetized. Examples are: iron, nickel, cobalt and chromium
North poles
Those poles which are attracted toward the earth's geographic North Pole
What is Direct Current?
Unidirectional flow of charge - flows in a constant direction.
What is the simplest way to measure emf of a device?
Using a slide-wire potentiometer.
Under what circumstances will we use an oscilloscope, instead of a voltmeter, to measure voltage?
We will be using it to measure AC (alternating current). The voltmeter can only be used to measure DC (direct current).
What is voltage called when measured by oscilloscope?
When voltage is measured by an oscilloscope it is called a signal. An oscilloscope plots voltage as a function of time.
Ohm's law states that current is given by the ratio of voltage/resistance. Did our data agree with that?
Yes, most of our experimental data is consistent with the math relationship.
A galvanometer does what?
- Is a meter used to detect small currents A galvanometer G is connected between points a and b.
State how the resistance of a wire depends on the wire's length and on its cross-sectional area?
- resistance is inversely proportional to cross-sectional area -resistance is directly proportional to the length the wire. The resistance of wire depends on its cross-sectional area because they are inversely proportional. If the wire is thinner the resistance is bigger. Doubling the wire area will half the resistance. -
What are some examples of electric multimeters?
-Voltmeter -Ammeter -Ohmmeter
Frequency equals?
1/period
Measurement using meters: What is a meter?
A meter is any device built to accurately detect and display an electrical quantity in a form readable by a human being. In the analysis and testing of circuits, there are meters designed to accurately measure the basic quantities of voltage (voltmeter), current (Ammeter), and resistance (ohmmeter).
What is a resistor?
A resistor is an electrical element or component that resists (or opposes) the flow of electrical current (the flow of electrons) in an electrical circuit. It is called variable because you can adjust the amount of resistance that it has.
Electric Circuit: What is a simple electric circuit?
A simple Electric Circuit is a closed connection of Batteries, Resistors, and Wires.
What is the difference between AC and DC?
DC stands for direct current and is the direct one way flow of electrical charge. Whereas, AC stands for alternating current and is the flow of electric charge that reverses direction.
What does resistivity of a material mean? Is it a constant?
Electrical resistivity (also known as resistivity, specific electrical resistance, or volume resistivity) quantifies how strongly a given material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electric charge. Resistivity is commonly represented by the Greek letter ρ (rho). It is a constant.
How does the dimmer switch work?
Every switch has a variable resistor to adjust the light level. Now vary the position of the tip of the wire to various points along the graphite core and observe what happens to the lightbulb. When you vary the position of the tip, you basically changing the length of the resistor (graphite) so as a result the current on the lightbulb changes following the equation I=V/R. In this set up, the voltage of the battery is not changing so the current in the lightbulb is inversely proportional to the resistor. Remember you make the resistance greater (increasing the length of the graphite) when you want a dimmer light setting and you make the resistance smaller when you want a brighter light setting.
What is the time constant if the ohms of a digital multimeter is 10 mohms and the capacitor is 1uF?
If the capacitor is 1uF and the internal resistance of the digital multimeter is 10 mega ohms, the time constant is r = RC (10 mega ohms)(1 uF) = 10 seconds
What happens if you increase the voltage? What happens if you decrease the voltage?
If you increase the voltage through a circuit whose resistance is fixed, the current goes up. If you decrease the voltage, the current goes down. -Resistance is known as a constant independent of both current and voltage. If the voltage is instead held constant, then the resistance and current in a circuit are inversely proportional to each other. Ohm's law expresses this relationship as a simple mathematical formula: V = IR
What happens as the light beam travels from point A to point B?
In Figure 1 a light beam travels from point A to point B from one medium whose index of refraction is n1 to another whose index of refraction is n2.The light ray intersects the interface at an angle θ1 which is measured with respect a line drawn perpendicular to the interface at the point of intersection. This line is called the "normal" or is a normal line to the surface.
Angle 1 of index of refraction 1 is called? Angle 2 of index of refraction 2 is called?
In Figure 1, the angle θ1 is called the angle of incidence and the angle θ2 is called the angle of refraction. (Diagram illustrating Snell's Law. A light ray intersecting an interface at an angle is refracted or bent when traversing from one medium to another and the amount of refraction is given by Snell's Law.)
Parallel circuit
In a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the currents through each component. (current through each of the components is different)
Series circuit
In a series circuit, the current through each of the components is the same, and the voltage across the circuit is the sum of the voltages across each component (voltage is different across each component - so sum has total)
What is the velocity of light in a vacuum?
In a vacuum the velocity of light is given the symbol c, v=c, and has the value
What is different about the potentiometer from measuring using only a voltmeter?
In an earlier experiment, a voltmeter was used to measure the voltage across a circuit element with the assumption that the voltmeter itself did not affect the measurement. This is not the case. The accuracy of the voltmeter reading depends on the instrument being used and the circuit on which readings are being made and, therefore, the current drawn with respect to the current in the circuit. We saw, also that the Emf (Electromotive force) of a source differed from the voltmeter reading because of the internal resistance of the source. A device which overcomes these drawbacks is the potentiometer.
What is a dimmer switch?
In its oldest and simplest form, a dimmer switch is a variable resistor.
For this experiment what happened?
In this experiment a rectangular plate of glass or plastic of width W is used to refract a ray of light that passes through it. See Figure 2. The ray is traced out on a sheet of paper, the angles are measured, and then the index of refraction of the material is calculated.
Line of force
Line showing the shape, direction, and relative strength of a magnetic field. The direction of the line at any point is the same as the direction of the magnetic field.
What is the region surrounding a magnet called?
Magnetic field
What does a galvanometer do?
Measures very small currents
Do lines of force cross each other? Explain
No, because each line of force goes in a specific direction and two lines of force do not occupy the same space.
If a small resistance is introduced in the circuit due to a poor contact between the battery and the binding post d, would this effect the calculated value of the unknown resistance?
No, it would not affect the calculated value because it is not directly involved in the bridge of the circuit.
Monopole
Nonexistent, so far as we know. A single magnetic north pole (without its southern counterpart) or a single magnetic south pole (without its northern counterpart). A monopole would be the magnetic equivalence of an electron or proton.
What are angles measured relative to?
Normal to surface...In optics, almost without exception, all angles are measured relative to a normal to a surface or interface between two media.
What happens if a ferromagnetic material is placed in a magnetic field?
Often, these domains are randomly oriented and cancel each other out, but if a ferromagnetic material is placed in a magnetic field, the domains line up and the material become magnetic. This induced magnetism can be temporary or permanent depending on the material.
What is the diagram showing?
Open circuit
A 6 μF capacitor is initially charged to 100 V and then connected across a 600 ohm resistor. a. What is the initial charge on the capacitor?
Q = CV C = 6 uF -> 6x10^-6 F (6x10^-6)(100V) = 6x10^-4 C
c. How much charge is on the capacitor after 6 ms?
Q(t) = Qoe^(-t/RC) (discharging eqn - connected across resistor) = (6x10^-4 C)(e^-6ms/3.6 ms) = 1.13x10^-4 C
R1 and R2 are?
R1 and R 2 are the resistances of segments of a long wire, along which the galvanometer probe will slide, known as the slide wire. The slide wire has uniform resistivity, ρ, which depends only upon the material the wire is made of and the temperature. The uniform circular cross-sectional area of the slide wire is represented by A. Hence the resistance per unit length is constant. Thus, the resistance of each segment of the slide wire is proportional to its length, L.
Domain
Regions in a material where magnetic effects add up, where the magnetic moments are all aligned
What is an RC Circuit?
Resistor Capacitor circuit - is an electric circuit composed of resistors and capacitors driven by a voltage or current source. A first order RC circuit is composed of one resistor and one capacitor and is the simplest type of RC circuit
How can the index of refraction be found in this experiment?
Since the index of refraction of light in air is approximately one, the index of the glass or plastic material can be found from Equation
How are slide-wire potentiometers different? What are the two features?
Slide-wire is different from a common wire in the sense that it has two important features that a common wire may not exhibit. 1. It has a very uniform diameter all along its length. 2. It is homogenous all along its length i.e. whatever alloy it is made of, the proportion of elements remain same all over the wire.
Some materials have what? What are the types of materials called and some examples?
Some materials have domains, areas where magnetic effects add up; these are ferromagnetic materials and are usually made of iron, nickel, cobalt, chromium dioxide.
When does the null galvanometer have a reading of zero?
The null galvanometer will have a reading of zero only when points a and b have no potential differences between them. Either the known resistor Rk or the ratio R2 R1 is adjusted until the voltage difference VAB is zero and no current flows through G. When VAB = 0, the bridge is said to be "balanced"
What is the magnetic flux?
The number of magnetic field lines drawn around magnets doesn't just depend on the mood of the illustrator. Technically, they are proportional to the amount of magnetic flux (magnetic field strength × area through which the lines pass). Since the magnetic field lines are concentrated around the poles, the flux would be greater there.
What does the potentiometer consist of?
The potentiometer consists of a long uniform wire with a constant current in it and a method for inserting, sequentially, a standard cell for calibration and the unknown cell for measurement.
How does a potentiometer work?
The potentiometer operates on the principle of adjusting opposing voltages until they are exactly equal. At that point the net current is zero and there is, therefore, no voltage drop because of any internal resistance.
Magnetic field
The region surrounding a magnet; this is the region in which magnetic forces due to the magnet are noticeable
What is the resistance?
The resistance of the wire is uniform and, therefore, any particular length, L, will have a resistance proportional to that length.
What does a Wheatstone Bridge measure?
The wheatstone bridge provides a very precise means of measuring resistance. It is a simple bridge circuit consisting of a source of emf, a galvanometer, and a network of four resistors. By balancing the bridge and knowing three of the resistances (or the ratio of 2 and knowing the third). the resistances of the fourth R can be calculated. An unknown resistance Rx, can be balanced against known resistance Rk and known ratio resistances of R, R2 until a galvanometer bridged across the parallel branches shows zero current. When the bridge is balanced, there can be no difference of potential between points C and D. "Differential resistance measurer"
What are the symbols used in electric circuits?
There is a standard set of symbols used to represent the various parts of a circuit. In circuit diagrams a battery is shown as two parallel lines, one longer than the other. The longer line is the positive terminal and the shorter line is the negative terminal.
Why are the symbols used?
These symbols are used to simplify the drawing of an electric circuit. The circuit shown below can be drawn as the circuit diagram by using these circuit diagram symbols.
What does it mean for the slide wire to have uniform resistance over its entire length?
This means that if a slide wire of length L has a resistance of R then a half-length of that wire will have a resistance R/2. This is important to convert the resistance into potential drop.
South poles
Those poles which are attracted toward the earth's geographic South Pole
Can you explain the purpose of the iron filings?
To determine which direction the magnetic field lines are going.
What does voltage do?
Voltage (V) gives a circuit its electrical potential, which means that voltage contributes to the movement of electrons throughout the circuit. High electrical potentials in a circuit are areas that have a new positive charge and areas with low electrical potentials in a circuit have a net negative charge.
If 200 cm long wire with the same resistance is used instead of the 100 cm long wire with the same resistance, does the sensitivity of the instrument change?
Yes, the length does effect the sensitivity of the instrument. As the length of the wire increases the sensitivity also increases.
If a small resistance is introduced in the circuit due to a poor contact between the bridge wire and the binding post d, would this effect the calculated value of the unknown resistance?
Yes, this would affect the calculated value of the unknown resistance because it would add more resistance to one side of the circuit. The calculated value would be off because the resistance per unit length would no longer be constant.
A light ray in air strikes water at an angle of incidence equal to 40°. If the index of refraction for water is 1.33, what is the angle of refraction?
n1 x sin1() = n2 x sin2 () (1.00xsin(40 deg))/(1.333) = 28.82 degrees n1 less than n2 angle 2 less than angle 1
What are the devices called?
sources of the electromotive force (emf)
How do you measure current?
1. Connect the multimeter to the decade box and to one end of a battery. (see diagram in previous section). 2. Set the decade box to 10 ! . 3. Connect the other end of the battery to the decade box. 4. Make sure the multimeter is set to measure amps. 5. Record the measured amps and the theoretical value. 6. Repeat this for the following settings: 15 ! , 20 ! (giving you three separate values).
How do you measure resistance?
1. Connect the multimeter to the decade resistance box. 2. Make sure the multimeter is set to measure ohms. 3. Set the decade box to 10 ! . 4. Record the measured ohms and the theoretical value. 5. Repeat this for the following settings: 100 ! , 1000 ! , and 10000 ! (giving you four separate values). 6. Connect the multimeter to a piece of wood. 7. Record the multimeter value. 8. Connect the multimeter to a piece of copper wire. 9. Record the multimeter value.
If one full sine wave has a length of 6.00 divisions on the screen of the oscilloscope, and the scope is set at 500 ms per division, what is the frequency of the wave? (recall that frequency f=1/T, where T is the period). a. 3.00 kHz b. 3.00 Hz c. 0.33 kHz d. 0.33 Hz
1. Determine the amount of T (also known as period) which is horizontal distance (length) x time. T = (6 cm)(500x10^-3 s) = 3 cm/s f = 1/(3 cm/s) = 0.33 Hz
How do you measure voltage using a multimeter?
1. Place the + lead on the + end of a battery. 2. Place the - lead on the - end of a battery. 3. Make sure the multimeter is set to measure volts. 4. Record the measured voltage and the theoretical value. 5. Repeat this for three other batteries (giving you four separate values). 6. Place the + lead on the + output of a power supply 7. Place the - lead on the - ground of a power supply 8. Set the power supply to any arbitrary value. 9. Record the measured voltage and the theoretical value. 10. Repeat this for three other settings (giving you four separate values).
How can a magnet become demagnetized?
A magnet can become demagnetized if something causes the domains to become unaligned, such as being dropped repeatedly or being placed in a magnetic field oriented in a different direction than that of the magnet.
What is a potentiometer?
A potentiometer is an instrument for measuring the potential (voltage) in a circuit. Before the introduction of the moving coil and digital volt meters, potentiometers were used in measuring voltage. The method was described by Johann Christian Poggendorff around 1841 and became a standard laboratory measuring technique
What are the components in an electric circuit?
A simple circuit contains at least three components: I. A source of electrical potential difference or voltage. (typically a battery or electrical outlet) II. A conductive path which would allow for the movement of charges. (typically made of wire) III. An electrical resistance (resistor) which is loosely defined as any object that uses electricity to do work. (a light bulb, electric motor, heating element, speaker, etc.)
What is a voltmeter?
A voltmeter measures electrical potential between its terminals. Voltmeters are always placed in parallel with the circuit or circuit element where the voltage measurement is desired. Since the voltage across two or more parallel elements is the same, the voltage measured by the meter will be the same as the element to which the meter is connected. When using a non-auto-ranging meter, select the highest possible range and reduce the range as necessary until the desired level of accuracy is reached. Always start with a range higher than the expected value to prevent damage to the meter.
All devices have what in common?
All devices such as; batteries, power supplies, motor-driven generators have two terminals between which there is a potential difference in the presence or absence of electrical currents.
What is an ohmmeter?
An ohmmeter measures the electrical resistance between its terminals. An ohmmeter is connected to the circuit or circuit element of interest after the element of interest has been isolated from the rest of the circuit. The element of interest has to be isolated from the rest of the circuit so that its resistance value isn't obscured by the resistance values of the other circuit components connected to the element of interest. Never connect an ohmmeter to an energized circuit or the meter could be destroyed.
Why did you point the magnet's South Pole toward the earth's north?
Because the compasses north is attracted to the south pole of the magnet and the magnet is representative of the earth's magnetic poles.
What is the overall relationship of Ohm's Law?
By maintaining a constant voltage, the electrical current that flowed through the circuit and the amount of resistance were inversely proportional to the other. As the resistance is increased in a circuit, the flow of electrical current is decreased. Meaning the resistor is acting as an insulator in the circuit. As the resistance is decreased in a circuit, the flow of electrical current is increased, which means the resistor is acting as a conductor in the circuit.
How do you measure current?
By placing the resistor in a series you can determine the flow of current. Each resistor (if you had multiple etc) in a series circuit has the same amount of current flowing through it. Which means you can measure the current like this. If the resistor is in parallel in a circuit the current flowing through each resistor in the parallel circuit is different.
How do you measure voltage?
By placing the resistor in parallel to the voltage you can determine the voltage across the resistor. Each resistor in a parallel circuit has the same full voltage of the source applied to it. The voltage drop across each individual resistor in a series is different, and their combined total adds up to the power source input.
What is a Cathode Ray?
Can be observed in vacuum tubes and are a stream of electrons.
emf's of an ideal source are?
Completely independent of the current between the terminals. For real sources however, this is not the case. emf's from a common battery and emf's of a commercial battery supply change with the current drawn from the source.
How is a galvanometer connected in a circuit to measure current? Draw a schematic representing its position in a circuit with one resistance and one battery source.
Connect a galvanometer in a series flowing from positive to negative.
The wheatstone bridge was invented by Samuel Hunter Christie in 1833 and improved and popularized by Sir Charles Wheatstone in 1843. Why didn't they simply use a digital multimeters to make their measurements like we have done in lab?
Digital multimeters were not made until 1920's and so the wheatstone bridge along with the galvanometer were the best way. The galvanometer was used to measure resistance and voltage by using a Wheatstone bridge, and comparing the unknown quantity to a reference voltage or resistance. "back in the day" this was the most sensitive way to measure a very small bridge change.
b. the current
First find initial current before discharge R = V/I (12 V)/(10x10^6 ohms) = 1.2x10^-6 A second find final I after discharge when t =RC(r) I(t) = Io(1-e^-t/RC) (1.2x10^-6 A)(1-e^-1) = 7.59x10^-7 A
What is the equation for a discharging capacitor?
For discharging process. It can be seen from this equation that after time t= R × C the voltage C will drop by a factor of 1/e. This time t, equals R × C is called the time constant of the circuit and is denoted by r.
A wheatstone bridge consists of?
Four resistors -The unknown resistor is Rx, the resistor Rk is known, and the two resistors R1 and R2 have a known ratio R2 and R1, although their individual values may not be known.
From this experiment - what is the mathematical relationship between current and resistance?
From the graph it showed that when voltage is constant the current and resistance are inversely proportional.
What happens to the plates on the capacitor when it is connected to a resistor and the switches are closed?
If a capacitor is connected to a resistor R by closing a switch S, as shown in Figure 3, the negative and positive Q stored on the plates are no longer prevented from neutralizing each other.
What happens when an alternating signal is applied to the vertical plates of the oscilloscope?
If an alternating signal is applied to the vertical plates of the oscilloscope it is possible that a pattern such as that shown in Figure 2 might be obtained. This particular wave shape is called a sine wave. The oscilloscope can be used to determine the peak AC voltage by measuring the height of the signal displayed. The frequency can be determined indirectly by determining the width of one cycle and the horizontal sweep time per unit length.
How do potentiometers work?
In this arrangement, a fraction of a known voltage from a resistive slide wire is compared with an unknown voltage by means of a galvanometer. The sliding contact or wiper of the potentiometer is adjusted and the galvanometer briefly connected between the sliding contact and the unknown voltage. The deflection of the galvanometer is observed and the sliding tap adjusted until the galvanometer no longer deflects from zero. At that point the galvanometer draws no current from the unknown source, and the magnitude of voltage can be calculated from the position of the sliding contact.
How does light travel?
Light travels with a velocity v where v, 𝜆, and 𝑓 are related by:
Can magnetic field lines overlap? Why?
Magnetic field lines can never cross because the lines point in only one direction at any place at any time.
What is magnetic flux and how is it related to magnetic field lines?
Magnetic flux is the product of the magnetic field strength times the perpendicular to the area it is in. Magnetic field lines are proportional to the magnetic flux.
What are some examples of magnets?
Magnetic materials possess a number of interesting characteristics and have been used in a wide variety of applications. The aurora borealis is caused by the earth's magnetic field. Magnets are used in motors, MRI's and in mag-lev trains like at Disney World.
Ferromagnetic
Material having the capability to be magnetized
A way of discharging a fully charged capacitor is to short the two plates with an electrical wire. Explain why this is useful way.
One plate on the capacitor holds the negative charge while the other plates hold the positive charges. The positive and negative charges are attracted to each other but never reach each other due to the dielectric between them, this is how the capacitor holds the charge. When a wire is placed on both ends the charges leave the capacitor resulting in the discharge of the capacitor.
What is the equation for percent error?
Percent error: Percent error is used when you are comparing your result to a known or accepted value. It is the absolute value of the difference of the values divided by the accepted value, and written as a percentage.
What is resistance?
Resistance (R) is a measure of the difficulty for electrons to flow through a circuit. Most materials can be used as resistors in a circuit as most have a certain level of resistance.
Resistors: What are resistors low in resistance and high in resistance?
Resistors low in resistance are called conductors and resistors high in resistance are known as insulators. Voltage then provides the flow of electrical current and resistors can prevent the level of flow at various levels.
A resistor, known to have a resistance of Rk = 20 kOhms, is placed in a Wheatstone Bridge with resistor of unknown resistance Ru. The point of zero current is found on the slide wire at a point where the length L, on the side with the known resistance is 25 cm, and the length L2 of the remaining wire is 75 cm. Find Ru using Ru/Rk = L2/L1 a. 6.7 kOhms b. 20 kOhms c. 40 kOhms d. 60 kOhms e. None of these
Ru = Rk(L2/L1) 20x10^3 ohms((75x10^-2)/(25x10^-2)) = 60,000 ohms (d) = 60 kOhms
The basic component of an oscilloscope is a cathode ray tube (CRT) - what is a CRT?
The CRT is a vacuum tube which uses thermionic emission to generate a beam of electrons which are emitted from the so called "electron gun" and accelerated toward a phosphor screen by placing a high positive potential on the accelerating anode. This produces a spot of light on the phosphor screen called the beam spot. The electron gun is actually nothing more than a coil of wire which heats up a cathode. When a current is passed through it causing it to emit electrons which are subsequently focused into a well- defined stream of electrons called a beam. The position of the electron beam may be adjusted using electric or magnetic deflection. In electric deflection, a potential is applied to the vertical and horizontal deflection plates. By adjusting the potentials on these plates, the beam spot position on the screen may be varied.
Who described the relationship between current, resistance and voltage? What is Ohm's Law?
The German physicist Georg Simon Ohm (1787-1854) was the first to demonstrate experimentally that the amount of electrical current flowing through an electric resistance for a given potential difference or voltage across the object is described by the following equation:
What are the units of magnetic fields?
The International System unit of field intensity for magnetic fields is Tesla (T). One tesla (1 T) is defined as the field intensity generating one newton (N) of force per ampere (A) of current per meter of conductor: Tesla (T) = N × A-1 × m-1 = kg × s-2 × A-1 Certain other non-SI units, like Gauss (G), are still occasionally used. A magnetic field of one tesla is quite strong. That is why magnetic fields are usually expressed in microtesla (μT).
What is a wheatstone Bridge?
The Wheatstone bridge is a circuit used to compare an unknown resistance with a known resistance. The bridge is commonly used in control circuits. It is used in the case of an electric circuit, we may want to know the amount of current which is passing through it. In this manner, the wheatstone bridge apparatus act as a balance-balancing the current of the two sides of a circuit.
How are both angle 1 and 2 related to each other?
The angles of incidence and refraction, θ1 and θ2, are related to each other by Snell's Law, which is given by
How can the deviation from the path be measured?
The deviation d of the original ray from its initial path, defined as the perpendicular distance between the initial path and the parallel final path, can be measured:
What is the direction of the magnetic field?
The direction of the magnetic field is the direction in which the north pole of a compass needle points if placed at that point, so magnetic lines of force show the direction an imaginary,singlenorth pole would travel if placed at a point on that line.
The earth is considered what?
The earth can be considered to have a large bar magnet along its north-south axis. This magnet would have its south pole pointing to what we call magnetic north and its north pole pointing to what we call magnetic south. ( Remember, the north pole of one magnet is attracted to the south pole of another, so the north pole of a compass points to a south magnetic pole, which is in our geographic northern hemisphere.) The direction we call north was originally determined with respect to the stars.
The farther away from the magnetic source you get...
The farther away from the magnetic source you get, the weaker the field is: B (magnetic field) is inversely proportional to r (distance).
The lines of force do what and start from what pole going to what pole?
The lines of force loop the magnet, emanating from the North Pole and returning at the South Pole (So, inside the magnet they go from south to north). The lines of force, therefore, are concentrated at these poles. Experiments show that like poles repel each other and unlike poles attract each other.
What is a multimeter?
The multimeter is a common multi-purpose instrument used to measure electrical quantities in a circuit. A circuit consists of components or devices connected electrically or electromagnetically along a closed pathway. When used to measure voltage, the multimeter is called a voltmeter and it measures the potential difference across two points ( in S.I. units called "Volts" symbolized with "V"). • When used to measure resistance, the multimeter is called an ohmmeter and it measures the resistance through an electrical component (in S.I. units called "Ohms" symbolized with " ! "). • When used to measure current, the multimeter is called an ammeter and it measures the current flowing (electrical flow) through a circuit (in S.I. units called "Amps" symbolized with "A").
Consider a DC source connected across a slide-wire resulting in a potential drop of 4V between two ends of the slide wire. The slide wire is 100 cm long and it is mounted over a meter stick so that one can read the length of the wire.
The unknown voltage Vx of a given battery can be calculated by multiplying Vs with a fraction of the wire's length between the positive end post and the point where the reading of the galvanometer is zero.
The position of the beam spot depends on what?
The vertical position of the beamlight spot on the face of a cathode-ray tube is determined by the magnitude of the voltage on the vertical plates, while the horizontal position is determined by the magnitude of the voltage on the horizontal deflection plates. Thus, the position of the beam spot depends upon the combination of these vertical and horizontal deflection voltages.
If you want to store two bar magnets, what orientation should they have with respect to each other so as not to weaken their magnetic fields?
They should be placed together with opposite poles facing each other. If the same poles were places together (north-north) the repelling forces would weaken the magnet.
Magnetic moment
Think of it as a little magnetic field created by an electron's orbit around the nucleus of an atom
Why is using a potentiometer the best way to measure the emf of a device?
This is because of the fact that the potentiometer measurements do not depend upon the internal resistance of the emf source.
What is the condition for zero current?
This is the condition for zero current. This requires that 𝑉𝑎𝑐 = 𝐼𝑘𝑅𝑘 must be the same as 𝑉𝑏𝑐 = 𝐼1𝑅1. Similarly, 𝑉𝑎𝑑 = 𝐼𝑥𝑅𝑥 must be the same as 𝑉𝑏𝑑 = 𝐼2𝑅2, where V =Voltage I=Current R = Resistance
What can you use to measure the voltage if the voltage supply is not steady or DC (direct current)?
To measure electrical voltage that is changing rapidly overtime an oscilloscope is used.
Overall compared to normal?
Usually, this means, that when a light ray travels from a less-dense medium to a more-dense medium, the light ray is bent toward the normal, and when it moves from a more- dense medium to a less-dense medium, the ray is bent away from the normal.
What is the potential drop within the battery if the internal resistance is 4.3 ohms and a current of 2.7 amperes is passed through it?
V = IR V = (2.7 A)(4.3 ohms) = 11.61 V
What is the equation for a charging capacitor?
V is the final value of the potential difference across the plates of the capacitor. The above two equations for the charging and discharging processes give most of the information needed to understand the process.
If the graph below represents the display of an oscilloscope, state what physical quantities are represented by the graph's horizontal axis and its vertical axis, respectively.
Voltage vs Time
Can we always measure the voltage using a voltmeter, no matter what?
We can only measure voltage using a voltmeter if the voltage supply is steady or DC (direct current).
What happens when a direct current (DC) power source is connected across the capacitor?
When a DC power source is connected across a capacitor the capacitor becomes charged. The charging, is not instantaneous, but follows an exponential behavior characteristic of the capacitance of the capacitor.
What happens when the charged capacitor is disconnected from the battery and connected across a resistor?
When a charged capacitor is disconnected form the battery and then connected across a resistor R, it become discharged. The current flows through R and discharging follows an exponentially decaying behavior which is characteristic of R and C. In this experiment we will study the time behavior of the charging and discharging of a capacitor in an RC circuit.
What happens when a resistor is used in a circuit?
When a variable resistor is used in a circuit to vary the brightness of a lightbulb, you make the resistance greater when you want a dimmer light setting and you make the resistance smaller when you want a brighter light setting. Resistance is increased by increasing the length of the path of resistive material through which the electrons have to flow, and is decreased by decreasing the length of the path.
What happens in the circuit when the charging is complete?
When charging is complete, V is equal to Vs and hence the active voltage is zero. Thus no current passes through the circuit after the charging process is over. The circuit is then equivalent to two batteries of the same output connected opposite to each other. The behavior of V or the current I passing through the circuit as a function of time is shown in figure 2.
What happens when light travels through one medium to another?
When light travels from one medium to another, through an interface between them, the speed of light changes depending on the indices of refraction of the two media.
What happens to the circuit when the switch in the circuit is closed?
When the circuit is completed by closing the switch S, the current I is divided at point c into two parallel branches cud and cad (fig 1). This is called a "bridge" circuit because the galvanometer is bridged across the two parallel branches cud and cad.
What happens if the index of refraction is greater than that of the first medium?
When the light ray enters the second material, the light ray will be bent toward the normal if the index of refraction of that material is greater than that of the first medium.
What happens to that charging circuit when the switch is closed?
When the switch S in Figure 1 is closed to complete the circuit, the charging starts. At any instant of time after the start of the charging process, the voltage which causes current to flow in the circuits is called an active voltage and it is equal to the source voltage Vs minus the voltage Vc across the capacitor at the instant. Thus the VA = Vs -Vc.
What happens when the voltage on the horizontal plates is increasing?
When the voltage on the horizontal plates is increasing at a constant rate with respect to time, the beam spot will move horizontally at a constant rate of speed. If, while this is happening, a fluctuating voltage is applied to the vertical plates, the beam spot will rise and fall in accordance with the fluctuation while it is moving horizontally. The resulting motion produces a trace of light on the face of the oscilloscope with the same shape as would a graph of the fluctuating voltage. If the wave shape of the fluctuating voltage is not known, the oscilloscope allows you to observe the shape of this unknown wave form.
What are the components in the equation?
Where λ0 (wavelength o) represents the wavelength of the light in vacuum and 𝑓 (f) remains the same frequency independent of the medium the light is traveling in. In a material or substance, light travels at a slower speed, and the ratio of the speed of light in vacuum to the speed of light in the material, Vc is defined as the index of refraction for that material, n, i.e.
A No. 5 American Wire Gauge (AWG) wire has a diameter of 4.621 mm. If it is made out of copper, which has resistivity p = 1.7x10^-8 Ohm meters, then what is the resistance R, of 1 meter of the wire? Use the equation R = p(L/A), where L is the wire's length and A is its cross-sectional area. Recall that the area of a circle is A = pir^2 (radius = r). a. 2.5x10^-4 ohms b. 0.001 ohms c. 8x10^-4 ohms d. 0.00001 ohms e. None of these
d = (4.621x10-3 m)/2 = 0.0023105 = r pi(0.0023105)^2 = 1.677x10^-5 m R = ((1.7x10^-8 ohms m)(1 m))/(1.677x10^-5 (b)= 0.001 ohms
