physics 104

In a Kirchoff loop, the voltage of a battery is treated as positive if the loop is traversed from Correct! the negative to positive terminal. either direction. the positive to negative terminal.

the negative to positive direction

If the charge on a capacitor is doubled, the energy stored in the capacitor is ! quadrupled. tripled. unchanged. doubled.

! quadrupled.

On average, an electric water heater (4.5 kW) operates for 1.5 hours each day. If the cost of electricity is $0.20/kWh, what is the cost of operating the heater during a 14-day period? $12.60 $0.90 Correct! $18.90 $40.5

$18.90

A solid conducting sphere is surrounded by a thick, spherical conducting shell. A total charge of -Q is initially placed and released at the center of the inner sphere. After equilibrium is reached, how much charge is on the outer surface of the shell?

-Q

Electric potential is a scalar. the same as electic field. the same as electric force. a vector.

a scalar.

A parallel plate capacitor has a capacitance of 2.0 micro-F with air between the plates. The capacitor is connected to a 9.0-volt battery and charged. The battery is then removed. When a dielectric is placed between the plates, a potential difference of 7.5 V is measured across the plates. What is the dielectric constant of the material? 0.83 1.0 1.7 Correct! 1.2

1.2

A silver wire is 0.3 m long and has a diameter of 0.05 cm. What is the resistance of the wire? 6.1x10^(-7) ohms 6.1x10^(-3) ohms 1.6x10^(-8) ohms 2.4x10^(-2) ohms

2.4x10^(-2) ohms

In a flashing neon sign display, the resistance is 5 million ohms, and the time constant is 6.0sec.Suppose you want a time constant of 3.0 sec. 15 million ohms 5 million ohms 10 million ohms Correct! 2.5 million ohms

2.5 million ohms

Two charges, +4.0 micro-C and +3.0 micro-C, are separated by a distance of 35 cm. What is the electric field halfway between the charges? 7.3x10^(4) N/C towards the +3.0 micro-C charge 2.9x10^(11) N/C towards the +4.0 micro-C charge Correct! 2.9x10^(5) N/C towards the +3.0 micro-C charge 2.9x10^(5) N/C

2.9x10^(5) N/C towards the +3.0 micro-C charge

A 200-ohm resistor is placed in a circuit with four identical batteries connected in series. If the resistor draws 4.0 A, what is the terminal voltage of each battery? 75 V 1600 V 100 V Correct! 200 V

200

A glass rod rubbed with silk acquires a charge of +7.0x10^(-9) C. How much mass is transferred from the rod? 4.0x10^(-20) 4.4x10^(10) Correct! 4.0x10^(-20) kg -4.0x10(-20) kg

4.0x10^(-20) kg

In a flashing neon light circuit, a time constant of 1.2 s is desired. If you have a 3.0 micro-farad capacitor, what resistance should you use in the circuit? 3.6x10^(-6) ohms Correct! 4.0x10^(5) ohms 4.0x10^(5) 2.5x10^(-6) ohms

4.0x10^(5) ohms

A three-way lightbulb can produce 30 W, 50 W, or 75 W of power at 60 V. What is the resistance of the lightbulb in the 75 W case? 1.25 ohms 60 ohms Correct! 48 ohms 75 ohms

48 ohms

For a given circuit voltage and 10 resistors, which situation provides the largest circuit current? Half the resistors in series, half in parallel (order doesn't matter). Correct! All of the resistors in parallel. All of the resistors in series. Pairs of resistors alternating between series and parallel.

All of the resistors in parallel.

Two charges of +3.5 micro-C are placed at opposite ends of a meterstick. Where on the meterstick could a free proton be in electrostatic equilibrium? Nowhere on the meterstick. Correct! At the 0.5 m mark. At either the 0 m or 1 m marks. At the 0.35 m mark.

At the 0.5 m mark.

Imagine two sets of charges; set A is made up of two electrons, and set B is made up of two protons. The two sets of charges are far from each other so they cannot affect one another. Which of the following is true?

The electric forces in both cases are repulsive

Connecting resistors in series always decreases the total resistance. True Correct! False

False

The resistivity and conductivity have no connection to each other. True Correct! False

False

With a battery, direct currents can sometimes flow from the anode to the cathode, but at other times they flow in the opposite direction. True Correct! False

False

How would you connect multiple batteries in order to get the biggest possible voltage? Correct! Put all of the batteries in series. It does not matter how you combine them. Put some in parallel and some in series. Put all of the batteries in parallel.

Put all of the batteries in series.

An object with charge -Q is placed in an electrically neutral metal cup (without touching the cup). Which of the following best describes the situation?

The electric field in the metal of the cup is zero, the charge in the metal is zero, and the surface charge is -Q.

Object A has a net charge of +Q. Object B has a net charge of +2Q. A positive test charge is first brought 1 m from object A. Object A is removed and the same test charge is brought 2 m from object B. Which of the following correctly describes the relative magnitudes of the electric fields experienced by the test charge?

The field due to object A is twice that due to object B.

Imagine two charges A and B. Charge A is drawn with 8 electric field lines coming from its surface. Charge B is drawn with 16 electric field lines coming from its surface. Which of the following is true?

The magnitude of charge B is twice as large as charge A.

You rub a balloon on your hair and it gains a net negative charge. Which of the following statements is true? Correct! The negative charge gained by the balloon has been lost by your hair, so the net change in the charge of the hair-balloon system is zero. The charge gained by the balloon was created by friction, so the net change in the charge of the hair-balloon system is negative. The charge gained by the balloon was created by induction, so the net change in the charge of the hair-balloon system is negative. The negative charge gained by the balloon is equal to the negative charge left on your hair, so the net change in the charge of the hair-balloon system is negative.

The negative charge gained by the balloon has been lost by your hair, so the net change in the charge of the hair-balloon system is zero.

How are electric potential difference (voltage) and electric potential energy related?

The voltage is the potential energy per unit positive charge.

Two parallel plates are a distance d apart with a constant electric field E between them. An electron with charge q is released from a point near the negative plate and is made to travel at constant velocity. Which of the following is correct?

The work done by the electric field as the charge moves is +qEd.

If you want to create a working battery, which one of the following options MUST occur? There must be equal numbers of electons at each electrode. Correct! There must be a larger excess of electrons at one electrode than at the other. There must be no voltage between the electrodes. There must be the same electric potential at each electrode.

There must be a larger excess of electrons at one electrode than at the other.

According to Ohm's law, a graph of voltage (y-axis) versus resistance (x-axis) would look like a straight line with a slope equal to the resistance value. a straight line with slope equal to the inverse of the current value. Correct! a straight line with slope equal to the current value. a straight horizontal line (constant value).

a straight line with slope equal to the current value.

When resistors are connected in parallel, the currents through each resistor are zero in all resistors but one. are all equal. are different with the largest current flowing through the largest resistor. Correct! are different with the largest current flowing through the smallest resistor.

are different with the largest current flowing through the smallest resistor.

In a closed circuit, the movement of electrons is best described as very fast straight-line motions in the direction of the current. Correct! basically random movement with a slow drift in the direction opposing the current. very fast straight-line motions in the direction opposing the current. basically random movement with a slow drift in the direction of the current.

basically random movement with a slow drift in the direction opposing the current.

Three resistors with values of 7.5 ohms, 9.0 ohms, and 20 ohms are connected in series in a circuit with a 12-volt battery. What is the current in each resistor? Correct! current in resistor 1=0.33 A, current in resistor 2=0.33 A, current in resistor 3=0.33 A. current in resistor 1=1.6 A, current in resistor 2=1.3 A, current in resistor 3=0.6 A current in resistor 1=1.6 A, current in resistor 2=1.6 A, current in resistor 3=1.6 A current in resistor 1=3.5 A, current in resistor 2=3.5 A, current in resistor 3=3.5 A

current in resistor 1=0.33 A, current in resistor 2=0.33 A, current in resistor 3=0.33 A.

For a fixed voltage, you can increase the power by Correct! decreasing the resistance. not changing the resistance. increasing the resistance.

decreasing the resistance.

The resistance of something depends only on its resistivity. is a fundamental property of a material. Correct! depends on its resistivity and its geometry. depends only on its geometry

depends on its resistivity and its geometry.

An electron volt measures electric potential difference. equipotential. electric field. Correct! energy.

electric potential difference.

Electric field lines are drawn parallel to equipotentials. False true

false

The only way for an object to have an electric charge is to have an excess of electrons.

false

Capacitors connected in series... (Choose ALL answers that are correct) Correct! must have the same charges. act like one capacitor with a capacitance equal to the sum of the individual capacitances. must have the same voltages. Correct! act like one capacitor with an inverse capacitance equal to the sum of the inverses of the individual capacitances.

must have the same charges. act like one capacitor with an inverse capacitance equal to the sum of the inverses of the individual capacitances.

If the potential increases most rapidly in the positive y-direction, the electric field points in the positive x-direction. positive y-direction. negative x-direction. Correct! negative y-direction.

negative y-direction.

By convention, the direction of an electric field at any point in space is determined by the direction of the electric force on a Correct! positive charge. neutral charge. negative charge.

positive charge.

The rear window defogger on your car works by Joule heating. If the current through those wires doubles, the heating power halves. doubles. stays the same. Correct! quadruples.

quadruples.

If you are charging an initially uncharged capacitor in an RC circuit, the voltage of the capacitor Correct! starts at zero and increases to the battery voltage. starts at the battery voltage and decreases to zero. remains at zero always. always remains equal to the battery voltage.

starts at zero and increases to the battery voltage.

Imagine an RC circuit that contains a fully charged capacitor. If the capacitor is discharged, the capacitor voltage is smallest and the circuit current is largest at the start of the discharge process. the capacitor voltage is largest and the circuit current is smallest at the start of the discharge process. the capacitor voltage and circuit current are smallest at the start of the discharge process. Correct! the capacitor voltage and circuit current are largest at the start of the discharge process.

the capacitor voltage and circuit current are largest at the start of the discharge process.

Capacitance increases as the charge increases and/or the voltage increases. the charge increases and/or the voltage decreases. the charge decreases and/or the voltage decreases. the charge decreases and/or the voltage increases.

the charge increases and/or the voltage decreases.

When charging a capacitor in an RC circuit, you expect Correct! the current to decrease with time. the current to stay constant. the current to increase with time.

the current to decrease with time.

When charging a capacitor in an RC circuit, you expect the current to stay constant. the current to increase with time. Correct! the current to decrease with time.

the current to decrease with time.

In a parallel plate situation, the voltage is 60 V. If the electric potential value at the negative plate is 60 V, then the electric potential value at the positive plate is 0 V. Correct! the electric potential value at the positive plate is 120 V. the electric potential value at the positive plate is 60 V. the electric potential value at the positive plate is -60 V.

the electric potential value at the positive plate is 120 V.

In a parallel plate situation, the voltage is 60 V. If the electric potential value at the negative plate is 60 V, then the electric potential value at the positive plate is 0 V. the electric potential value at the positive plate is 60 V. the electric potential value at the positive plate is 120 V. the electric potential value at the positive plate is -60 V.

the electric potential value at the positive plate is 120 V.

The resistance in a conductor like copper increases with length because the electrons can be absorbed more easily. they have farther to go without colliding with atoms. Correct! the electrons have more opportunity to bounce off of atoms and not participate in the overall flow. the electric force decreases with increasing distance.

the electrons have more opportunity to bounce off of atoms and not participate in the overall flow.

Look at Fig. 19.10(b). If the charge q3 moved closer to charge q1 along the dashed line, the net force vector would gain an upward vertical component and its horizontal component would decrease. Correct! the net force vector would gain an upward vertical component and its horizontal component would increase. the net force vector would remain unchanged. the net force vector would gain a downward vertical component and its horizontal component would increase.

the net force vector would gain an upward vertical component and its horizontal component would increase.

In order to "jump start" a dead car battery, the anodes and cathodes of the dead battery and a good battery are connected in parallel with jumper cables. In this situation, the total voltage available to the dead car is twice as large as that of the good battery. the total voltage available to the dead car is 4 times as large as that of the good battery. Correct! the total voltage available to the dead car is the same as that of the good battery. the total voltage available to the dead car is half that of the good battery.

the total voltage available to the dead car is the same as that of the good battery.

Two objects with opposite charges are fixed in place (they cannot move). If the charge on the negative object doubles and the positive object's charge remains the same, only the force on the negative charge increases by a factor of 2. Correct! then the force on both charges increases by a factor of 2. only the force on the positive charge increases by a factor of 2. then the force doesn't change because the objects are fixed.

then the force on both charges increases by a factor of 2.

In a Kirchoff loop, if the loop direction and current direction coincide for a resistor, the voltage is considered to be negative. Correct! True False

true

The units of the time constant are ohm-farad. One ohm-farad equals one second. Correct! True False

true

A charged object is brought near a neutral electroscope. If the leaves separate, you know that the object is electrically neutral. you know that the object has a net negative charge. Correct! you know that the object has a net electric charge. you know that the object has a net positive charge.

you know that the object has a net electric charge.