PHY 112 Lab Quizzes
How were the different current measurements compared in part 2 of last week's lab?
% diff= |Am-Ap|/ ((1/2)|Am+Ap|)`
What two conditions may be true of a magnetic field that is known to be including a voltage, and therefore a current, in a given wire configuration?
1. magnetic field may be in motion 2. magnetic field may be change over time
Write out the Thin Lens equation with all variables clearly defined below and briefly explain why it is called this below.
1/s +1/s'=1/f 1/s=object distance 1/s'= image distance 1/f= focal length
Write out the Thin Lens equation used in today's Thin Lenses lab, as well as both equations used for magnification below.
1/s+1/s'=1/f, Mh=h'/h, Ms=s'/s
Why is it appropriate to use 2.00 V as the accepted value when calculating percent error in part 3 of the Electric Charges, Potentials, and Fields lab?
2.00 V is the charge directly in the center of the charge paper. The multimeter was set to 4.00 V so 2.00 V is in the center of the conducting zones.
The time constant t is the time it takes the capacitor to discharge to _______% of its fully charge voltage, as well as the time it takes to charge to ______% of its maximum voltage.
37, 63
How will the potential difference between points A and B differ from the potential difference between point C and D in the diagram to the right?
A and B are close so they'll have a higher potential difference in comparison to C and D A and B the same C and D the same
Why is using a Pasco sensor to measure current or voltage better than using a multimeter?
A pasco sensor allows you to print out your reading. It is also more accurate because a multimeter is reading waves.
Define the two terms: a) Diffraction b) Interference
A) a wave of any kind that bends around an obstruction in its path B) when more than one wave obeys the principle of superposition at a particular point in space, the amplitudes of each wave adds to form the amplitude of the resultant wave
What is the difference between AC and DC power supplies?
AC is alternating current like a wall outlet and DC is direct current like a battery
If the image created by a particular lens is inverted and half the size of the original object, what is the numerical value for the magnification of the lens?
About 0.5
Clearly and concisely summarize the procedure for measuring capacitance C by using the voltage vs. time graph of a charging capacitor in DataStudio.
Allow the capacitor to charge to Vmax, then discharge to zero. Using DataStudio find the slope of the line of the voltage vs time graph. C=IM c=capacitance,I= current,M=slope
Clearly and concisely summarize the procedure for measuring the time constant t using the voltage vs time graph of a discharging capacitor in Data Studio.
Allow the capacitor to charge to Vmax, then discharge to zero. Using DataStudio smart tool find V37 and the time. Subtract T37 from T0 to get T.
Which physical quantity is represented by the slope of the line in the V vs. I plot given below?
As V increases so does I represents resistance
How does the magnetic field due to a bar magnet vary with distance from the magnet as shown below? Express in your own words, mathematically, or graphically.
As d increases the magnetic field decreases
Give the equation used for the magnetic field generated inside a solenoid; define all factors.
B=(m0)(n)(I) B=magnetic field M0= 4pix10^-7 n=# of turns I=current
The magnetic field of a single wire loop is given by phi=BAcostheta. Define the variables.
B=magnetic field A=area of wire theta= angle of magnetic field and area
Give the name and a brief description of the physical attribute used to determine the capacitance C of the discharging capacitor in today's lab.
C=I/M m is the slope obtained from the voltage vs time graph. you can also use the corner of the peak to determine the maximum voltage and time it took to discharge
To which types of lenses can the Thin Lens equation be applied to? Give a brief description of each type below.
Concave= creates image due to being curved inward convex= lens is curved outward
What are the dependent and independent variables of the graph that is plotted in part 2 of today's lab? How is the slope of that graph used to determine the turns per unit length of the solenoid?
Dependent: B Independent: distance (l) Turns per length: Slope=B/I
Briefly summarize the method used to describe the magnetic flux in the 3rd part of the Magnetic Induction lab.
Determine the magnetic field from DataStudio. Find the area of the solenoid. Multiply these two values to find magnetic flux. phi=BA
Briefly summarize the method used to determine the magnetic flux from the voltage vs time graph in the second part of the Magnetic Induction lab
Determine the pharaoh and area and divide by the number of turns. Perform five trials to find the average. phi=A/N
Write the equation for Faraday's law and clearly explain its meaning in your own words.
E=dt/dΦ magnetic field must be in motion and change over time. stationary fields do not create a magnetic flux
The voltage vs time graph below represents the voltage induced in a solenoid while dropping a bar magnet through it. What does the highlighted area physically represent? What about the area that is not highlighted or not, has the most area under it?
Highlighted: first end drops through the solenoid Not highlighted: the second end coming out of the solenoid most area: both areas are equal
Give the formulas for current I and impedance Z used in today's lab below.
I=V/Z V/sqrt of R^2 + (XL-XC)^2 Z= sqrt of R^2+ (XL-XC)^2
Using the figure indicate which direction the current goes in the coil.
It goes to the left because the magnetic field goes into the board.
What will happen to the magnetic field if the current that creates it is reversed?
It will be reserved as well
Another property of lenses is magnification. Give both mathematical expressions used to represent magnification below, and a brief description of how to use each.
Mh=h'/h uses object and image height Ms=s'/s uses object and image distance
Of the 2 ways to find M in part 1 of the Thin Lenses lab, which one (heights or distances) would be more reliable? Explain why.
Ms=s'/s Mh=h'/h distance is more reliable because it was easier to measure using the rail rather than the ruler
Write the equations for Ohm's Law and Resistivity below.
Ohm's Law: V=IR Resistivity: P= RA/l
The thin lenses lab consists of 2 experimental parts. Give a brief description of each part.
Part 1: determine the focal length and magnification of a converging convex lens Part 2: determine the focal length and magnification of a converging concave lens
Electric field lines are always _________ to equipotential lines.
Perpendicular
Write the formula used to calculate charge.
Q=CV Q=charge C=capacitance V=voltage
What type of values for voltage (or current) must be used when applying Ohm's law to AC circuits?
RMS values for both current and voltage
Resistors R1 and R2 have resistances to 36 ohms and 60 ohms, respectively. Find RE for each of the cases below. Show your work for each case.
Req=R1+R2=36+60=96ohms Req=(R1xR2/R1+R2)=(36x60)/(36+60)=22.5 ohms
Was the equivalent resistance RE, high when R1 and R2 were in series or parallel in the 2nd part of the Ohm's Law lab activity? Explain
Series because the resistance in a series circuit is evenly passed through both resistors compared to a parallel circuit where the charge is unevenly distributed
How would the magnetic field strength B change if the solenoid used in lab were twice as long and the current through I was disabled, but still only had 1340 total turns? Justify your answer.
The 2's would cancel causing B to remain the same. B=(m0) (n/L) (i0)
Explain what happens physically to the charges on the ice pail.
The charge returns to neutral once the positive wand is removed.
In the 3rd part of the Ohm's Law lab activity, which of the measured values is the most unreliable?
The most unreliable value was the length of the pencil lead because the alligator clips could not be precisely clipped on the lead. The further away the clips were the more resistivity.
Briefly explain how to determine the peak values for voltage (or current) using a multimeter in the Impedance lab.
The multimeter gives the RMS voltage or current values and these values must be multiplied by the sqrt of 2 to find the peak voltage or current.
Briefly explain how to determine RMS values of voltage (or current) signals using Data Studio in the impedance lab.
The peak of the voltage and current signals can be found with the smart tool function. These values are then divided by the sqrt of 2 to find the RMS values.
Briefly describe the physical conditions used to determine the resonance frequency in part 2 of the resonance lab.
The quantities must be equal in order for the resonance frequency to be determined. Xl=XC VL=VC
Give the name and a brief description of the procedure used to determine the direction of a magnetic field generated by an electric current, or vice versa?
The right hand rule, which is where your thumb pints in the direction of the electric current and the rest of the hand is folded in direction of magnetic field
To which port on the multimeter should the red probe be connected to in order to measure voltage?
V1 ohm's port
Write down the equation for Ohm's Law and give the name and units of each variable.
V=IR v= volts (v) I= current (A) R=resistance (ohms)
Write out the equation for Ohm's law applied to a series RLC circuit of frequency f that contains a resistor R, a capacitor with reactance Xc, and an inductor with reactance Xl.
V=IZ= I(sqrt R^2+(Xl-XC)^2) Z=v/I Xc=(1/2)(pifrC) V=IR Xl=2pifrL
In today's Electromagnetic Induction lab, Faraday's law is given by V=-N (delta theta/delta t). Define all the variables.
V=voltage N=# of turns delta theta/ delta t= change of magnetic flux/ change in time
Briefly explain the meaning of Vmax and VRMS used in today's lab, and how are they related?
VRMS is the average of V accounted for the different values of V in AC circuit. VRMS: Vmax/sqaureroot 2
Give a brief definition or physical explain of a virtual image.
Virtual image- where the reflected lines seems to diverge but isn't the real image
Briefly explain the phase relation between a circuit's input current and the voltage across a capacitor Vc and between the input current and the voltage across an inductor Vl.
Vl leads I by 90 degrees Vc lags I by 90 degrees
In an AC circuit with only a resistor, voltage and current are in phase. Give a brief physical description of what it means for voltage and current signals to be in phase.
Voltage and current signals must follow each other at their minimum and maximum
For today's experiment, list below the 2 devices that can be used to measure voltage, as well as the 2 devices that can be used to measure current.
Voltage: multimeter and pasco voltage current: pasco current and multimeter
How are these values related to the peak or maximum values for voltage (or current)?
Vrms=Vmax/sqrt2 Irms=Imax/sqrt2
Describe how to determine the relationship between the magnetic field of a bar magnet and the distance from the magnet in part 1 of today's Magnetic Fields lab.
We will measure the magnetic field of a bar magnet at various lengths. These measurements will the be compared to determine the relationship between length and magnetic field.
What is the precise symbol of the multimeter mode you used to measure: a) AC current b) DC voltage
a) A (with waves over the top) b) V (with both straight and dotted lines)
Give the mathematical expressions for capacitive and inductive reactance below, as well as brief description of the physical effects of any reactance on any circuit.
a) Capactive :XC=(1/2)(pi)(f)(c) b)inductive:XL= 2 pi fl c) physical effects add resistance to the total resistance (impedance) of a series RLC circuit
It is possible to use the Thin Lens equation on multiple lenses in a row in order to find the focal length of a compound lens. For a system of 2 lenses, give the mathematical expression for the magnification of the compound lens and briefly explain how to apply the Thin Lens equation in that system in order to determine its focal length. a)magnification b)finding focal length
a) Ms=s'/s; Mh=h'/h; M=M1M2 b) 1/s+1/s' =1/f focal length was used by determining the inverse of the sum of image and object height
Briefly describe the phase relation, at resonance between... a) the input current nd the voltage across the inductor (VL) b) the input current and the voltage across the capacitor (VC) c) the voltages across the inductor and capacitor (between VL and VC)
a) Vl leads by 90 degrees b) VC lags by 90 degrees c)voltages across the inductor and capacitor (between VL and VC) they are equal in magnitude but opposite in signs
State and briefly describe the type of circuit connection needed to measure: a) current b) voltage
a) series (A) b) parallel (V)
Explain the 2 techniques used to measure the resistance in the first section of today's lab. a) multimeter b) ohm's law
a) set the multimeter to resistance mode (ohms) b) R= V/I
When using the acrylic rhombus to test Snell's law in the Geometrical Optics lab, what happens to the angle of refraction when a) the angle of incidence is increased? b) the angle of incidence is decreased? c) the index of refraction of the air, n1, is increased? d) the index of refraction of the rhombus, n2, is decreased?
a) theta r increases b) theta r decreases c) theta increases d) theta r increases
Briefly describe how the maximum or peak current is determined in part 1 and 2 of the resonance lab.
a. part 1: multimeter is used to obtain rms values for current and then multiplied by sqrt 2 for peak b. part 2: locate the peak current using DataStudio and Smart tool
State the mathematical expression of Ohm's law for a series RLC circuit at any frequency. Then give the Ohm's law expression for when that circuit is tuned to its resonant frequency.
any freq: V=IZ= +or- sort of R^2 + (XL+XC)^2 resonant freq: V=IZ= I sort R^2
Give the mathematical expressions for capacitive and inductive reactance below, as well as a brief description of the physical effects of any reactance on a circuit.
capacitive: Xc=(1/2)pifrC inductive: Xl=2pifrL Physical effects: add more resistance (z-impedance) for an AC capacitor
Write down the equations for a charging and a discharging capacitor below.
charging: Q=Qm(1-e^-t/RC) discharging: Q=Q0(e^-t/RC)
Which type of mirror has a focal length f that equals half of its radius of curvature R?
concave and convex
In terms of the way they make light behave, what is the difference between concave and convex mirrors?
concave: are shaped in a curvature form convex: are shaped in a more circular form
What is the difference between charging by conduction and charging by induction?
conduction-direct contact occurs causing a transfer of charge induction- the charged object is close enough to transfer the charge
List both types of mirrors that are the easiest to describe and produce, and explain why it is so easy to do so for these types of mirrors below.
convex and concave both of these mirrors possess symmetry
In the graph of voltage vs. time below, which represents the voltage induced in a solenoid while dropping a bar magnet through it, explain below why the induced voltage is stronger for the second peak than it is for the first? Why is one peak positive, the other negative?
first peak: induced voltage is stronger due to its speed of the changing of the magnetic field one is negative because the North pole of the magnet was placed into the negative end of the solenoid one is positive due to the opposite magnetic flux
Using the simple properties of flat mirrors (or lens boundaries), explain how to describe mirrors (or lenses) that have more complicated shapes below.
flat mirrors: haves less complicated shaped due to being a flat surface convex: are curved in an outward formation creating both a real and virtual image concave: are curved inward creating a virtual image on top of a real image
What is the main property of a lens? What 2 physical parameters create this property?
focal length object distance image distance
State the mathematical expression for the resonant freq. of a series RLC circuit.
fr= 1/2pi sqrt LC
If you are given two charged objects, one positively charged and one negatively charge, in which direction do the electric field lines always point?
from positive to negative
Which 2 units are used for magnetic fields; what factor is needed to convert between them?
guess and tesla 1T=10,000 G
Describe how the impedance of a series RLC circuit is affected when it is tuned to resonance.
impedance is at its min and current at its max
If the voltage in a circuit increases, but the resistance remains the same, then the current will
increase
What physical property of light will be determined in today's lab? List both methods used to determine it.
it's wave nature diffraction and interference
State the name of the law, as well as its equation with all variables defined, that governs the basic behavior of all mirrors below.
law of reflection: theta i= theta r i=angle of incidence r= angle of reflection
State the name of the law, as well as its equation with all its variables defined, that governs the basic behavior of all lenses below.
law of refraction/ snell's law n1sintheta i= n2 sintheta t i=angle of incidence t=angle of transmission n1 and n2 indices of refraction
Write the Si unit for all the following: Length, cross-sectional area, current, applied voltage, resistivity
meters (m) 3.14 r^2 =m^2 amps (A) Volts (V) Resistivity (ohmsxm)
Give the equation for Snell's Law, with each variable clearly defined, and precisely explain what the law physically means below.
n1sintheta i= n2sintheta r n1 and n2: index of refraction angles are angles of incidence and reflection
The two symbols below on the left are used to describe the direction of the magnetic field. Which symbol represents the magnetic field going into the page; which represents coming out of the page?
out of the board is the dot in the circle into the board is the x in the circle
Write down the equations for the equivalent capacitance for 2 capacitors in parallel and series below.
parallel: ceq= c1+c2 series: ceq= (c1xc2)/c1+c2
Write both mathematical expressions and the units used in lab for magnetic flux below.
phi=A/N A: area of the voltage (V) phi: magnetic flux N: #of turns phi=BA phi: magnetic flux B: magnetic field (T) A: area of wire (m^2) Unit: wb
What physical quantity is calculated and compared using a percent difference calculation in part 1 of the Resonance lab?
resistance
What physical condition of resonance is used to determine the resonant frequency of the circuit in part 1 of the Resonance lab?
resonant frequencies reached when the current peak is at its max when frequency is increased, the current is decreased
Write two equations for equivalent resistance Re below: the first equation for two resistors R1 and R2 in series, and the second equation for R1 and R2 in parallel.
series: Req= R1+R2 parallel: Req=(R1xR2/R1+R2)
Clearly explain Lenz's law below. How is Lenz's law represented mathematically?
the current induced by a magnetic field in a wire will create a magnetic field whose magnetic flux opposes the original magnetic flux (the neg sign in Faraday's law) V= -N (delta theta/delta t)
Which physical qualities will be measured in the last section of today's lab; which are calculated?
the percent difference between experimental and theoretical values of the resistivity of carbon
What can be said about the total charge of a closed system if it is conserved?
the total charge is constant and at zero
What is the physical property responsible for chemical reactions and electrical phenomena?
the transferring of charge (whether negative or positive) from one object to another
What physical condition of resonance is used to detained the resonant frequency of the circuit in part 2 of the resonance lab?
the voltage across the inductor and capacitor has the same height allowing them to have the same magnitude but opposite signs
Give the equation for the law of reflection, with each variable clearly defined, and precisely explain what the law physically means below.
theta i= theta r i=angle of incidence r=angle of reflection the angle of incidence equals the angle of the reflected ray on a flat surface
Give a brief description of capacitance, its units, and the equation that governs capacitance below. Clearly define all variables used in the equation.
units: Farads (F) Equation: C=Q/V c=capacitance, q=charge, v= potential difference definition: capacitance is the ability of a capacitor to hold a charge
Describe the connections needed to measure voltage and current in a circuit with a multimeter or any other device.
voltage: parallel current: series connection
Give the name and SI units of the 3 physical quantities that can be measured with a multimeter.
volts (V) resistance (ohms) current (A)
How would you change C in order to double the time it takes an RC circuit to discharge?
you would double C
How would you change R in order to cut in half the time it takes an RC circuit to charge?
you would half R