Chapters 22 and 23: Electrostatics and Electric Currents
Unit of Measurement for Electric Potential Energy
1 Volt = 1 Joule/1 Coulomb.
In a circuit of two lamps in series, where the current through one lamp is 1 A, what is the current through the other lamp? Defend your answer.
1 amp. The same current flows through lamps in series.
Characteristics of series circuit
1. Electric current through a single pathway. 2. Total resistance to current is the sum of individual resistances. 3. Current is equal to the voltage supplied by the source divided by the total resistance of the circuit. 4. The total voltage impressed across a series circuit divides among the individual electrical devices in the circuit so that the sum of the "voltage drops" across the resistance of each individual device is equal to the total voltage supplied by the source. 5. The voltage drop across each device are proportional to its resistance. 6. If one device fails, current in the entire circuit ceases.
Characteristics of Parallel Circuit
1. Voltage is the same across each device. 2. The total current in the circuit divides among the parallel branches. The amount of current in each branch is inversely proportional to the resistance of the branch. 3. The total current in the circuit equals the sum of the currents in its parallel branches. 4. As the number of parallel branches is increased, the overall resistance of the circuit is decreased. 5. A break in one path does not interrupt the flow of charge in the other paths.
How much energy is given to each coulomb of charge that flows through a 1.5-V battery?
1.5 joules
What are the Voltage Standards in the US?
120 V
What are the Voltage Standards in Europe?
220 V
Three-Wire Service
220-240 V, Washing Machine, Dryer, and Oven.
If a voltage of 6 V is impressed across the circuit in the preceding question and the voltage across the first lamp is 2 V, what is the voltage across the second lamp? Defend your answer.
4 volts. The sum of the voltages across each lamp must add up to the total voltage across both lamps.
Consider a circuit with a main wire that branches into two other wires. If the current is 10 A in the main wire and 4 A in one of the branches, how much current is in the other branch?
6 A
In a circuit of two lamps in parallel, where there is a voltage of 6 V across one lamp, what is the voltage across the other lamp?
6 volts
A diode converts ac to pulsed dc. What electrical device smoothes the pulsed dc to a smoother dc?
A capacitor
What is the Van de Graaff Generator?
A common laboratory device for producing high voltages and creating static electricity.
How does one coulomb of charge compare with the charge of a single electron?
A coulomb of charge is the charge associated with 6.25 × 1018 electrons.
Semiconductors
A material that can be made to behave sometimes as an insulator and sometimes as a conductor.
What is a positive ion? What is a negative ion?
A positive ion is a neutral atom that has lost one or more electrons. A negative ion is a neutral atom that has gained one or more electrons.
How does a semiconductor differ from a conductor or an insulator?
A semiconductor is neither a good conductor nor a good insulator - it has a middle range of resistivity.
What is a transistor composed of, and what are some of its functions?
A transistor is made of thin layers of semiconducting materials sandwiched together. It can be a switch, an oscillator, or an amplifier.
Which molecule is an example of a common electric dipole?
A water molecule
Between a watt, a kilowatt, and a kilowatt-hour, which is a unit of power and which is a unit of energy?
A watt is power, a kilowatt is power, and a kilowatt-hour is energy.
A spherical cavity is hollowed out of the interior of a neutral conducting sphere. At the center of the cavity is a point charge, of positive charge q. A. What is the total surface charge q int on the interior surface of the conductor (i.e., on the wall of the cavity)? B. What is the total surface charge q ext on the exterior surface of the conductor? C. What is the magnitude E int of the electric field inside the cavity as a function of the distance r from the point charge? Let k , as usual, denote 14πϵ0 . D. What is the electric field Eext outside the conductor? E. The total surface charge on the wall of the cavity, q int. F. The total surface charge on the exterior of the conductor, qext : G. The electric field within the cavity, Ecav : H. The electric field outside the conductor, Eext :
A. -q B. +q C. kq/r2 D. the same as the field produced by a point charge q located at the center of the sphere E. would not change F. would not change G. would not change H. would change
What is meant by saying that charge is quantized?
All charged objects have a charge that is an integer multiple of the charge of an electron.
How does the charge of one electron compare to that of another electron? How does it compare with the charge of a proton? How do the masses of protons and electrons compare?
All electrons have the same charge. Electron charge is equal and opposite to the proton charge. A proton has 1800 times the mass of an electron.
How is the direction of an electric field indicated with electrical field lines?
Always directed in the direction that a positive test charge would be pushed or pulled if placed in the space surrounding the source charge. Since electric field is a vector quantity, it can be represented by a vector arrow.
In terms of net charge, how does an electrically polarized object differ from an electrically charged object?
An electrically polarized object can have zero net charge, while a charged object cannot have zero net charge.
Circuits
Any path along which electrons can flow from the negative terminal to the positive terminal.
When you buy a water pipe in a hardware store, the water isn't included. When you buy copper wire, electrons
Are already in the wire.
Protons
Are positive electric charges. Repel positives, but attract negatives.
Gaps
Are usually in the form of a switch.
Safety Fuses
Are wires that melt when the given current is exceeded. Are connected in series along the supply line to prevent overloading in circuits. Are replaced by circuit breakers in modern buildings.
Suppose that the strength of the electric field about an isolated point charge has a certain value at a distance of 1 m. How will the electric field strength compare at a distance of 2 m from the point charge? What law guides your answer?
At twice the distance the field strength will be 1/4. the inverse-square law
Negative ion
Atom gaining one or more electrons has negative net charge.
Positive ion
Atom losing one or more electrons has positive net charge.
Electrons in an atom that are Outermost are...
Attracted loosely and can be easily dislodged.
Electrons in an atom that are Innermost are...
Attracted very strongly to oppositely charges atomic nucleus.
Circuit Breaker
Automatic switch that turns off when the current is excessive.
Why is there no electric field at the center of a charged spherical metal ball?
Because of mutual repulsion, mobile electrons in the conductor will spread out uniformly over the outer surface of the ball, so the force and the field on a test charge at the center is zero because opposing forces balance in every direction.
How can you charge an object negatively with only the help of a positively charged object?
By induction; Bring the positively charged object near the object to be charge and the far side of the uncharged object will become positively charged.
Potential Difference
Charge flows from one end to the other.
What kind of charging occurs when you slide your body across a plastic surface?
Charging by friction occurs. Electrons are transferred when one object rubs against another.
What are Resistors
Circuit elements that regulate current inside electrical devices.
Circuit
Complete path for energy to flow
Flow of charged particles in metal wires
Conduction electrons are charge carriers that are free to move throughout atomic lattice.
Unit for Charge
Coulombs (C)
When you double the voltage in a simple electric circuit, you double the
Current
What is an AC (Alternating) Current?
Current flows in a reversing pattern
What is Direct Current?
Current flows in one direction only
Formula for Power
Current x Volatge
Electric Shock
Damaging effects of shock result from current passing through the body.
Your friend says that a battery supplies the electrons in an electric circuit. Do you agree or disagree? Defend your answer.
Disagree. All matter has atoms, all atoms have electrons. What the battery does, is supply the potential difference to make existing electrons move.
Why will dust be attracted to a DVD wiped with a dry cloth?
During the wiping process either electrons are transferred to the cloth from the CD or from the CD to the cloth. In either case the CD becomes charged. The charge produces an electric field which polarizes dust particles near it and the polarized dust particles are then attracted to the charged CD.
How much energy is given to each coulomb of charge passing through a 2- V battery?
E = 2 J
A droplet of ink in an industrial ink-jet printer carries a charge of 1.4×10−10C and is deflected onto paper by a force of 3.2×10−4N. Find the strength of the electric field to produce this force.
E = 2.3×106 NC
Electric Potential Formula
Electric Potential = electric potential energy/amount of charge.
Capacitator
Electrical energy can be stored in this common device.
Capacitor
Electrical energy can be stored in this common device.
What are the differences between gravitational and electrical forces?
Electrical forces may be either attractive or repulsive. Gravitational forces are only attractive.
In the phenomenon of superconductivity, what happens to electrical resistance at low temperatures?
Electrical resistance disappears.
What charge is moving during Charge Polarization?
Electrons
Why are materials such as glass and rubber good insulators?
Electrons are tightly bound to their atoms, making them poor conductors of heat.
What happens when the Capacitor to a charging device?
Electrons are transferred from one plate to the other.
Alternating Current
Electrons in the circuit are moved first in one direction and then in the opposite direction, alternating to and fro about fixed positions.
At what speed do electrons in a battery driven automotive circuit travel along a wire? At what speed does the electric field propagate along a wire?
Electrons move at 0.01 cm/s. The electric field propagates at nearly the speed of light.
What happens to electrons in any charging process?
Electrons transfer from one place to another.
What term is used for "electricity at rest"?
Electrostatics
When you make your household electric payment at the end of the month, are you billed for voltage, current, power, or energy?
Energy
Electric Potential (Voltage)
Energy per charge possessed by a charged particle due to its location.
Electric Potential Energy
Energy possessed by a charged particle due to its location in an electric field. Work is required to push a charged particle against the electric field of a charged body.
Two pellets, each with a charge of 0.80 microcoulomb (8.0×10−7 C ), are located 2.4 cm (2.4×10−2 m ) apart. Find the electric force between them.
F = 10 N
Two point charges are separated by 6.2 cm . The attractive force between them is 30 N. Find the force between them when they are separated by 12 cm. Why can you solve this problem without knowing the magnitudes of the charges?
F = 8.0 N
Two point charges, each with 0.1 C of charge, are 0.6 m apart. Given that k=9.0×109N⋅m2/C2 (the proportionality constant for Coulomb's law), select the correct equations that show that the force between the charges is 2.5×108N .
F= kq1q2/r2=(9.0×109N⋅m2/C2)⋅(0.1C)⋅(0.1C)/(0.6m)2 =2.5×108N
Two point charges, each with 0.9 C of charge, are 0.1 m apart. Given that k=9.0×109N⋅m2/C2 (the proportionality constant for Coulomb's law), select the correct equations that show that the force between the charges is 7.29×1011N .
F= kq1q2/r2=(9.0×109N⋅m2/C2)⋅(0.9C)⋅(0.9C)/(0.1m)2 =7.29×1011N
Atomic physicists ignore the effect of gravity within an atom. To see why, calculate and compare the gravitational and electrical forces between an electron and a proton separated by 10−10m . The charges and masses are given in the textbook.
Felec/Fgrav = 2⋅1039
Electronic types neglect the force of gravity on electrons. To see why, compute the force of Earth's gravity on an electron and compare it with the force exerted on the electron by an electric field of magnitude 5000 V/m (a relatively small field). The mass and charge of an electron are given in the textbook.
Felec/Fgrav = 9.0×1013
Direct Current
Flows in one direction only. Electrons always move from the negative terminal towards the positive terminal.
Series Circuit
Forms a single pathway for electron flow between the terminals of the battery, generator, or wall outlet
Parallel Circuit
Forms branches, each of which is a separate path for the flow of electrons.
Examples of Semiconductors
Germanium and Silicon
Give two examples of common force fields and name the sources of these fields.
Gravity fields made by mass, electric fields made by charge
How does the heat emitted by lamps affect their efficiency?
Heat emitted reduces the efficiency.
Electric Potential (voltage)
High voltage can occur at low electric potential energy for a small amount of charge. High voltage at high potential energy occurs for lots of charge.
Calculate the current in the 220- Ω filament of a bulb connected to a 100- V line.
I = 0.45 A
Calculate the current in the 220- Ω filament of a bulb connected to a 120- V line.
I = 0.55 A
Using the formula power = current × voltage, find the current drawn by a 1000- W toaster connected to 130 V . Then, using the equation current = voltage/resistance, find the resistance of the toaster.
I = 7.7 A. As rounded R = 17 Ω. As rounded
Your friend says that the equivalent (combined) resistance of resistors connected in parallel is always less than the resistance of the smallest resistor. Do you agree?
I agree, because even for the smallest resistor, currents have an alternative paths making it possible for a smaller resistance.
What kind of charging occurs during thunderstorms?
Ice crystals are charged by friction and the ground is charged by induction.
Charging by Induction
If you bring a charged object near a conducting surface, electrons are made to move in the surface material, even without physical contact.
What is an electric dipole?
In an electric dipole, positive and negative charges are separated on opposite sides of an object.
Conservation of Charge
In any charging process, no electrons are created or destroyed. Electrons are simply transferred from one material to another.
Electric potential energy is measured in joules. Electric potential, on the other hand (electric potential energy per charge), is measured
In volts
Where do the electrons come from that produce an electric shock when you touch a charged conductor?
Inside you
Factors affected electrical resistance
Inversely proportional to cross-sectional area: Thin wires, more resistance than thick wires. Directly proportional to length: Doubling the length, doubles the resistance. Material: Rubber-much more resistance than the copper of the same size. Temperature: The higher the temperature, the more resistance.
Van de Graaff generator
Is a common laboratory device for producing high voltages and creating static electricity is called this.
Electric Potential Difference
Is the difference in potential between two points.
Electricity
Is the name given to a wide range of electrical phenomena
What does it mean to say that a certain current is 60 Hz?
It alternates back and forth 60 times a second.
What happens when you discharge a capacitator?
It can shock you
As in the video, we apply a charge + Q to the half-shell that carries the electroscope. This time, we also apply a charge - Q to the other half-shell. When we bring the two halves together, we observe that the electroscope discharges, just as in the video. What does the electroscope needle do when you separate the two half-shells again?
It does not deflect at all.
What is the function of the round third prong in a modern household electric plug?
It grounds the case to zero potential.
Does heating a metal wire increase or decrease its electrical resistance? Why?
It increases resistance because atoms at higher temperatures jostle into the way of moving electrons.
What property of a diode enables it to convert ac to pulsed dc?
It is a one-way valve that allows electrons to in one direction only.
If the resistance of a circuit remains constant while the voltage across the circuit decreases to half its former value, what change occurs in the current?
It is cut in half.
If the voltage impressed across a circuit is held constant while the resistance doubles, what change occurs in the current?
It is cut in half.
Unit for Potential Energy
Joules (J)
When two identical lamps in a circuit are connected in parallel, the total resistance is
Less than the resistance of either lamp.
LED
Light Emitting Diode
Why are lightning rods normally at a higher elevation than the buildings they protect?
Lightning rods are taller in order to be closer to the clouds, closer to lightning.
Two glass marbles (1 and 2), each supported by a nylon thread, are rubbed against a piece of silk and then are placed near a third glass marble (3), also supported by a similar thread. Assuming that marble 3 has not been in contact with the piece of fabric, which of the following statements best describes the situation when the three marbles are brought together? To keep things simple in this Tutorial, we will ignore the effects of polarization and just focus on the overall charge of each object.
Marbles 1 and 2 repel each other, but no interaction occurs with marble 3.
Superconductors
Materials acquire zero resistance (infinite conductivity) to flow of charge.
Insulators
Materials in which electrons are tightly bound and belong to particular atoms and are not free to wander about among other atoms in the material.
Conductor
Materials where the electrons in the outmost energy level are free to wander in the material
What are Superconductors?
Materials with zero electrical resistance of the flow of charge. Flow of charge is without generation of heat.
Only a small percentage of the electric energy fed into a common lightbulb is transformed into light. What happens to the remaining energy?
Most of the energy, more than 90%, of the electrical energy in an incandescent lamp goes directly to heat.
Why does a wire that carries electric current become hot?
Moving electrons collide with atoms, which transfers their kinetic energy to atomic motion.
Water is a partially what charged molecule?
Negative
Electrons
Negative electric charges. Repel negatives, but attract positives.
What is meant by conservation of charge?
Net charge cannot be created or destroyed.
What is the most common net charge of an atom?
Neutral
Neutrons
Neutral electric charge
How is Coulomb's law similar to Newton's law of gravitation? How is it different?
Newton's law of gravitation is attractive, whereas Coulomb's law is attractive or repulsive. Both are proportional to the inverse square of distance.
Is it necessary for a charged body actually to touch the ball of the electroscope for the leaves to diverge? Defend your answer.
No, it's not necessary for a charged body actually to touch the ball of the electroscope for the leaves to diverge. When you touch the charged object with the ball, some electrons flow from the body to the ball and you can observe a deflection in the electroscope.
A balloon may easily be charged to several thousand volts. Does that mean it has several thousand joules of energy? Explain.
No. Energy is voltage times charge, so you need a coulomb of charge to get several thousand joules of energy.
What is the unit of electrical resistance?
Ohm
According to Coulomb's law, a pair of particles that are placed twice as far apart will experience forces that are
One-quarter as strong
Central Rule of Electricity
Opposite charges attract one another; like charges repel.
Calculate the power of a hair dryer that operates on 160 V and draws a current of 8.0 A .
P = 1300 W
Calculate the power of a hair dryer that operates on 70 V and draws a current of 8.0 A .
P = 560 W
When you brush your hair and scrape electrons from your hair, the charge of your hair is
Positive
Why do Electric Fields go near the electric charge?
Positive charges in the Electric Field will go away
Flow of charged particles in fluids
Positive ions and electrons constitute electric charge flow
What is the relationship among electric power, current, and voltage?
Power is current times voltage.
Which particle has exactly one quantum unit of charge?
Proton
When one material is rubbed against another, electrons jump readily from one to the other but protons do not. Why is this? (Think in atomic terms.)
Protons are held tightly within the nucleus.
Two point charges are separated by 5.4 cm . The attractive force between them is 18 N . Suppose that the charges attracting each other have equal magnitude. Rearrange Coulomb's law and find the magnitude of each charge.
QQ = 2.4×10−6 CC
Electric Power
Rate at which electric energy is converted into another form.
What are High-temperature superconductors?
Refers to ceramic materials that can carry much current at a low voltage.
Coulomb's Law
Relationship among electrical force, charge, and distance discovered by Charles Coulomb in the 18th century
Ohm's Law
Relationship between voltage, current, and resistance. States that the current in a circuit varies in direct proportion to the potential difference, or voltage, and inversely with the resistance.
Electric Field Direction
Same direction as the force on a positive charge. Opposite direction to the force on an electron.
Electric Field Lines
Same direction as the force on a positive charge. Opposite direction to the force on an electron.
Two common types of Gaps
Series: Single Path. Parallel: Separate Paths
Total Resistance
Sum of individual resistors
How does the flow of current differ in a superconductor compared with the flow in ordinary conductors?
Superconductors have infinite conductivity (current flows forever), whereas ordinary conductors have a small resistance to the flow of electric charge.
Electric Field
Talks about the space surrounding an electric charge
The circuit within an incandescent lamp is shown. Which of the battery arrangements will light the lamp?
The 3rd one
If a 60-W bulb and a 100-W bulb are connected in series in a circuit, across which bulb will there be a greater voltage drop? How about if they are connected in parallel?
The 60 W light bulbs has more resistance than the 100 W light bulbs. In series, both bulbs would get the same amount of current. So the 60 W light bulb would get more voltage since V=IR. If they were connected in parallel, they would both have the same voltage.
Measurements show that there is an electric field surrounding Earth. Its magnitude is about 100 N/C at Earth's surface, and it points inward toward Earth's center. From this information, can you state whether Earth is negatively or positively charged?
The Earth is negatively charged
What would happen to the two balls if both of them had a non-neutral charge and you slowly increased the mass of the balls?
The angle of the balls with respect to the vertical would decrease.
What would happen to the two balls if one of them were kept positively charged and the charge on the other ball were slowly made increasingly negative?
The balls would begin to move closer together.
What would happen to the two balls if one of them were kept positively charged and the charge on the other ball were slowly increased, making it more and more positive?
The balls would begin to move farther apart.
Does a battery produce dc or ac? Does the generator at a commercial power station produce dc or ac?
The battery is dc; the generator is ac.
When charges mutually repel and distribute themselves on the surface of conductors, what becomes of the electric field inside the conductor?
The charges arrange themselves to make the field inside the conductor zero.
How is the direction of an electric field defined?
The direction of the field is the direction of the force on a positive test charge.
Why does the gravitational force between Earth and Moon predominate over electrical forces?
The electric force between Earth and Moon cancels out because they have an equal number of positive and negative charges.
Why do clothes often cling together after tumbling in a clothes dryer?
The electrons get rubbed off some items onto others.
Where is the energy stored in a capacitor?
The energy is stored in the electric field between the plates.
In which of the circuits shown does a current exist to light the bulb?
The fifth one
When you double the charge on only one of a pair of particles, what effect does this have on the force between them? Does the effect depend on the sign of the charge?
The force is multiplied by 2 compared to its original value, no matter the sign of the original charges.
When you double the charge on both particles in a pair, what effect does this have on the force between them? Does it depend on the sign of the charge?
The force will become four times greater.
Something gets "used up" in a battery that eventually dies and goes flat. One friend says that current is used up. Another friend says that energy is used up. Who, if either, do you agree with, and why?
The friend who says energy is used up is correct.
How does the size of the battery voltage affect the value?
The greater the battery voltage, and the larger and closer the plates, the greater the charge that can be stored.
The proportionality constant k in Coulomb's law is huge in ordinary units, whereas the proportionality constant G in Newton's law of gravitation is tiny. What does this indicate about the relative strengths of these two forces?
The huge value of the constant k for electrical force indicates a relatively huge force between charges, compared with the small gravitational force between masses and the small value of the gravitational constant G.
What happens to a lamp when you take both ends of the wire connected to it and hold them to the same side of the 12-volt terminal of battery, and why?
The lamp does not light up because there is no voltage difference applied across it.
What happens when you have a voltage difference between the two ends of the lamp, and why?
The lamp lights up because there is a voltage difference applied to it.
A glass marble is rubbed against a piece of silk. As a result the piece of fabric acquires extra electrons. What happens to the glass marble?
The marble has lost the same number of electrons acquired by the piece of silk. The marble acquires a positive charge and attracts the piece of silk.
A crystal of salt consists of electrons and positive ions. How does the net charge of the electrons compare with the net charge of the ions? Explain.
The net charge of the negative electrons has the same magnitude as the net charge of the ions.
What is meant by drift velocity?
The net flow of electrons along a wire.
Which part of an atom is positively charged, and which part is negatively charged?
The nucleus is positively charged and the electron cloud is negatively charged.
Why are metals good conductors of both heat and electricity?
The outer shell electrons in metals are free to move from atom to atom.
The leaves of a charged electroscope collapse in time. At higher altitudes, they collapse more rapidly. Why is this true? (Hint: The existence of cosmic rays was first indicated by this observation.)
The reason the leaves of an electroscope collapse at lower altitude is that the excess electric charge bleeds off into the moisture (electrical conductor) of the atmosphere. At high levels of the atmosphere, cosmic rays from space are more likely to produce ions (they are more energetic due to less collisions as they travel to the lower levels of the atmosphere which has a higher density of particles). The ions are produced when the high energy cosmic rays knock away an electron. Ions are charged particles and are electrically conductive and bleed off the charge from an electrical at a faster rate than normally.
How do the currents through the branches of a simple parallel circuit compare with the current in the voltage source?
The sum of the currents in the branches equals the current through the source.
What two things can be done to increase the amount of flow in a water pipe? Similarly, what two things can be done to increase the current in an electrical circuit?
The two things that can be done to increase the amount of flow in a water pipe are the higher pressure to lower pressure system and using a pump to increase water flow, or increasing the diameter of the pipe. To increase electrical flow increase voltage or increase width of the wire to decrease the resistance to electrons.
Will a lamp with a thick filament draw more current or less current than a lamp with a thin filament?
Thick filament has less resistance and will draw more current than a thin wire connected across the same potential difference.
Why are thick wires rather than thin wires usually used to carry large currents?
Thick wires have less electrical resistance and will carry greater amounts of current without overheating.
A tipped domino sends a pulse along a row of standing dominoes. Is this a good analogy for the way electric current, sound, or both travel?
This is the way sound travels but not how electric current travels.
Consider a lamp powered by a battery. Charge flows
Through both the battery and the lamp.
Diode
Tiny electronic device that acts as a one-way valve to allow electron flow in any one direction.
What is the primary purpose of a lightning rod?
To prevent a fire caused by lightning
What is the function of fuse or circuit breaker in a circuit?
To prevent over loading the circuit with current
Voltage Formula
V = EPE/Q
What is the current in a circuit dependent on
Voltage and electrical resistance in ohms.
Current
Voltage supplied divided by total resistance.
Unit for Voltage
Volts or V
A pipe is filled with water, and there is a piston at each end. If you apply unequal pressures at the two pistons, which way will the water flow in the pipe?
Water will flow from the piston with the higher pressure to the piston with the lower pressure.
What are units for Power?
Watts
How does wetness affect the resistance of your body?
Wet bodies have lower resistance.
When is the charging process complete?
When the potential difference between the plates equals the potential difference between the battery terminals. The battery voltage.
Your electronics friend needs a 20- Ω resistor but has only 40- Ω resistors. He tells you that he can combine them to produce a 20- Ω resistor. How?
When you combine resistors, there power goes up. You would be combining the strengths together.
Suppose you leave your car lights on while at a movie. When you return, your battery is too "weak" to start your car. A friend gives you a jump-start with his battery and battery cables. What physics is occurring here?
When you jumpstart a car you making an electrical current flow from the positive battery in your friends car into the dead battery in your car. The current then flows from the bad battery's terminal into the starter of the car, therefore, starting it.
How do electrical field lines indicate the strength of an electric field?
Where the field lines are close together, the electric field is stronger than where they are farther apart.
Will water flow more easily through a wide pipe or a narrow pipe? Will current flow more easily through a thick wire or a thin wire?
Wide pipe and thick wire
What is the error in saying the source of electrons in a circuit is the battery or generator?
Wires are full of mobile electrons.
Your friend says that the equivalent (combined) resistance of resistors connected in series is always more than the resistance of the largest resistor. Do you agree?
Yes, he is right because when resistors are combined in series, a current must travel through each of them to reach is destination and the total drop in voltage is the sum of the drops across all the resistors.
When combing your hair, you scuff electrons from your hair onto the comb. Is your hair then positively or negatively charged? How about the comb?
Your hair is positively charged while the comb becomes negatively charged.
When the filament breaks in one lamp in a parallel circuit, lamps in other branches of the circuit normally _________.
continue glowing as brightly
Your friend says that a battery supplies the electrons in an electric circuit. Do you agree or disagree? Defend your answer.
disagree; the electrons are already there
When the filament breaks in one lamp in a series circuit, other lamps in the circuit normally _________.
go out
Two pellets, each with a charge of 0.80 microcoulomb (8.0×10−7 C ), are located 2.4 cm (2.4×10−2 m ) apart. What would be the mass of an object that would experience this same force in Earth's gravitational field?
m = 1.0 kg
Charge Polarization
slight separation of the positive and negative charge in a neutral object when a charged object is brought near
What is the flow of current proportional to?
voltage difference between the two ends of the wire
