PHY 104 Exam 1

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? 1. 200 V 2. 100 V 3. 1600 V 4. 75 V

1. 200 V

Imagine you are measuring the electric field of a negative point charge. When you place your field measuring instrument 1 m away from the charge you measure a magnitude of 2 N/C. What does your instrument read when you are 0.5 m away? 1. 8 N/C. 2. 0.5 N/C. 3. 2 N/C. 4. 4 N/C.

1. 8 N/C

Kirchoff's junction theorem is a restatement of which of the following physical laws? 1. Conservation of charge. 2. Conservation of mass. 3. Conservation of momentum. 4. Conservation of energy.

1. Conservation of charge

How would you connect multiple batteries in order to get the biggest possible voltage? 1. Put all of the batteries in series. 2. Put all of the batteries in parallel. 3. Put some in parallel and some in series. 4. It does not matter how you combine them.

1. Put all of the batteries in series.

Imagine two charges A and B. Charge A is drawn with 8 electric field lines coming from its surface (like Figure 15.12b). Charge B is drawn with 16 electric field lines coming from its surface. Which of the following is true? 1. The magnitude of charge B is twice as large as charge A. 2. The magnitude of charge A is 4 times as large as charge B. 3. The magnitude of charge A is twice as large as charge B. 4. The magnitude of charge B is 4 times as large as charge A.

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

If you want to create a working battery, which one of the following options MUST occur? 1. There must be a larger excess of electrons at one electrode than at the other. 2. There must be no voltage between the electrodes. 3. There must be the same electric potential at each electrode. 4. There must be equal numbers of electons at each electrode.

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

In a Kirchoff loop, if the loop direction and current direction coincide for a resistor, the voltage is considered to be negative. 1. True 2. False

1. True

According to Ohm's law, a graph of voltage (y-axis) versus resistance (x-axis) would look like 1. a straight line with slope equal to the current value. 2. a straight line with slope equal to the inverse of the current value. 3. a straight line with a slope equal to the resistance value. 4. a straight horizontal line (constant value)

1. a straight line with slope equal to the current value.

Capacitors connected in series... (Choose ALL answers that are correct) 1. act like one capacitor with an inverse capacitance equal to the sum of the inverses of the individual capacitances. 2. must have the same charges. 3. act like one capacitor with a capacitance equal to the sum of the individual capacitances. 4. must have the same voltages.

1. act like one capacitor with an inverse capacitance equal to the sum of the inverses of the individual capacitances. and 2. must have the same charges.

For a fixed voltage, you can increase the power by 1. decreasing the resistance. 2. increasing the resistance. 3. not changing the resistance.

1. decreasing the resistance.

Imagine an RC circuit that contains a fully charged capacitor. If the capacitor is discharged, 1. the capacitor voltage and circuit current are largest at the start of the discharge process. 2. the capacitor voltage is smallest and the circuit current is largest at the start of the discharge process. 3. the capacitor voltage is largest and the circuit current is smallest at the start of the discharge process. 4. the capacitor voltage and circuit current are smallest at the start of the discharge process.

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

The resistance in a conductor like copper increases with length because 1. the electrons have more opportunity to bounce off of atoms and not participate in the overall flow. 2. they have farther to go without colliding with atoms. 3. the electrons can be absorbed more easily. 4. the electric force decreases with increasing distance.

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

For resistors in parallel, 1. the voltages across each resistor are equal. 2. the current only flows through one resistor. 3. the individual voltage drops across the resistors add up to the total voltage. 4. the currents through each resistor are equal.

1. the voltages across each resistor are equal.

A 6.0-volt battery is connected to a parallel plate capacitor with plate areas of 0.3 meters-squared each and a plate separation of 10 mm. How much energy is stored in the capacitor? 1. 8.2x10^(-10) J 2. 4.9x10^(-9) 3. 4.8x10^(-9) J 4. 1.6x10^(-9) J

3. 4.8x10^(-9) J

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? 1. $40.50 2. $0.90 3. $12.60 4. $18.90

4. $18.90

For a given circuit voltage and 10 resistors, which situation provides the largest circuit current? 1. All of the resistors in series. 2. Pairs of resistors alternating between series and parallel. 3. Half the resistors in series, half in parallel (order doesn't matter). 4. All of the resistors in parallel.

4. All of the resistors in parallel.

In household circuits, ground (neutral) wires 1. are at non-zero potential and carry current. 2. are at non-zero potential and carry no current. 3. are at zero potential and carry no current. 4. are at zero potential and carry current.

4. are at zero potential and carry current.

Circuit breakers in home electrical systems prevent 1. large resistances from occurring and stopping current flow. 2. weak currents from flowing and not providing enough power. 3. large voltages from building up in the house circuit. 4. large currents from flowing and increasing the risk of Joule heating-induced fires.

4. large currents from flowing and increasing the risk of Joule heating-induced fires.

If the potential increases most rapidly in the positive y-direction, the electric field points in the 1. negative x-direction. 2. positive y-direction. 3. positive x-direction. 4. negative y-direction.

4. negative y-direction.

If you are charging an initially uncharged capacitor in an RC circuit, the voltage of the capacitor 1. remains at zero always. 2. always remains equal to the battery voltage. 3. starts at the battery voltage and decreases to zero. 4. starts at zero and increases to the battery voltage.

4. starts at zero and increases to the battery voltage.

Determine the value of the potential 3.50 mm from the positive plate of a pair of parallel plates separated by 12.0 mm and connected to a 18.0-volt battery. 1. 18.0 V 2. 12.8 V 3. 8.50 V 4. 5.25 V

2. 12.8 V

What is the voltage across ten 2.0 V batteries when they are connected in parallel? 1. 5.0 V 2. 2.0 V 3. 10 V 4. 20 V

2. 2.0 V

1 / 1 point You rub a balloon on your hair and it gains a net negative charge. Which of the following statements is true? 1. The charge gained by the balloon was created by induction, so the net change in the charge of the hair-balloon system is negative. 2. 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. 3. 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. 4. The charge gained by the balloon was created by friction, so the net change in the charge of the hair-balloon system is negative.

2. 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.

When resistors are connected in parallel, the currents through each resistor 1. are different with the largest current flowing through the largest resistor. 2. are different with the largest current flowing through the smallest resistor. 3. are zero in all resistors but one. 4. are all equal.

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

Relative to the vacuum value, a dielectric always 1. decreases the capacitance. 2. increases the capacitance. 3. doubles the capacitance. 4.leaves the capacitance unchanged.

2. increases the capacitance.

The rear window defogger on your car works by Joule heating. If the current through those wires doubles, the heating power 1. stays the same. 2. quadruples. 3. halves. 4. doubles.

2. quadruples.

In a Kirchoff loop, the voltage of a battery is treated as positive if the loop is traversed from 1. the positive to negative terminal. 2. the negative to positive terminal. 3. either direction.

2. the negative to positive terminal.

A charged object is brought near a neutral electroscope (Fig. 15.4) . If the leaves separate, 1. you know that the object is electrically neutral. 2. you know that the object has a net electric charge. 3. you know that the object has a net positive charge. 4. you know that the object has a net negative charge.

2. you know that the object has a net electric charge.

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? 1. +Q 2. No charge 3. -Q

3. -Q

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? 1. 0.83 2. 1.0 3. 1.2 4. 1.7

3. 1.2

A platinum wire is 0.3 m long and has a diameter of 0.05 cm. What is the resistance of the wire? 1. 1.3x10^(-2) ohms 2. 3.8x10^(-5) ohms 3. 1.5x10^(-1) ohms 4. 3.8x10^(-2) ohms

3. 1.5x10^(-1) 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? 1. 2.9x10^(11) N/C towards the +4.0 micro-C charge 2. 7.3x10^(4) N/C towards the +3.0 micro-C charge 3. 2.9x10^(5) N/C towards the +3.0 micro-C charge 4. 2.9x10^(5) N/C

3. 2.9x10^(5) N/C towards the +3.0 micro-C charge

A glass rod rubbed with silk acquires a charge of +7.0x10^(-9) C. How much mass is transferred from the rod? 1. -4.0x10(-20) kg 2. 4.0x10^(-20) 3. 4.0x10^(-20) kg 4. 4.4x10^(10)

3. 4.0x10^(-20) kg

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? 1. The electric forces in set A are repulsive, but the forces in set B are attractive. 2. The electric forces in set A are attractive, but the forces in set B are repulsive. 3. The electric forces in both cases are repulsive. 4. The electric forces in both cases are attractive.

3. The electric forces in both cases are repulsive.

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? 1. The work done by the electric field as the charge moves is -qEd. 2. The work done by the electric field as the charge moves is zero. 3. The work done by the electric field as the charge moves is +qEd.

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

In a closed circuit, the movement of electrons is best described as 1. basically random movement with a slow drift in the direction of the current. 2. very fast straight-line motions in the direction of the current. 3. basically random movement with a slow drift in the direction opposing the current. 4. very fast straight-line motions in the direction opposing the current.

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

In order to measure the current passing through a resistor, an ammeter should 1. have a very large internal resistance 2. be connected in parallel, or "across", the resistor 3. be connected in series, or "in-line", with the resistor 4. have a resistance equal to that of the resistor being measured.

3. be connected in series, or "in-line", with the resistor

An electrically neutral object (like a balloon) 1. can be subjected to repulsive electric forces only. 2. can be subjected to attractive electric forces only. 3. can be subjected to electric forces due to polarization. 4. cannot be subjected to electric forces because it is neutral.

3. can be subjected to electric forces due to polarization.

In order to measure the voltage drop due to a resistor in a circuit, a voltmeter should be 1. connected in series, or "in-line", with the resistor. 2. connected only to the wire through which the current leaves the resistor. 3. connected in parallel, or "across", the resistor. 4. connected to the battery or voltage source.

3. connected in parallel, or "across", the resistor.

As the current increases, the electric power provided by a battery 1. decreases first, then increases. 2. decreases. 3. increases. 4. stays the same.

3. increases.

Capacitance increases as 1. the charge increases and/or the voltage increases. 2. the charge decreases and/or the voltage increases. 3. the charge increases and/or the voltage decreases. 4. the charge decreases and/or the voltage decreases.

3. the charge increases and/or the voltage decreases.

When charging a capacitor in an RC circuit, you expect 1. the current to increase with time. 2. the current to stay constant. 3. the current to decrease with time.

3. 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 1. the electric potential value at the positive plate is -60 V. 2. the electric potential value at the positive plate is 0 V. 3. the electric potential value at the positive plate is 120 V. 4. the electric potential value at the positive plate is 60 V.

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

If the distance between two equal positive charges doubles, 1. the magnitude of the electric force decreases by a factor of 2. 2. the magnitude of the electric 3. the magnitude of the electric force decreases by a factor of 4. 4. the magnitude of the electric force increases by a factor of 4.

3. the magnitude of the electric force decreases by a factor of 4.

Look at Fig. 15.8(b). If the charge q3 moved closer to charge q1 along the dashed line, 1. the net force vector would gain a downward vertical component and its horizontal component would increase. 2. the net force vector would remain unchanged. 3. the net force vector would gain an upward vertical component and its horizontal component would increase. 4. the net force vector would gain an upward vertical component and its horizontal component would decrease.

3. 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, 1. the total voltage available to the dead car is twice as large as that of the good battery. 2. the total voltage available to the dead car is half that of the good battery. 3. the total voltage available to the dead car is the same as that of the good battery. 4, the total voltage available to the dead car is 4 times as large as that of the good battery.

3. 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, 1. only the force on the negative charge increases by a factor of 2. 2. then the force doesn't change because the objects are fixed. 3. only the force on the positive charge increases by a factor of 2. 4. then the force on both charges increases by a factor of 2.

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

If it takes +3.5x10^(-5) J to move a positive charge between two charged plates, what is the magnitude of the charge if the plate are connected to a 9.0-volt battery? 1. 2.7 micro-C 2. zero 3. -3.9 micro-C 4. -2.7 micro-C 5. .3.9 micro-C

5. .3.9 micro-C

A 3.00 micro-farad capacitor, when connected to a 24V power supply, is charged to 63% of its final voltage in 2.0sec. What is the voltage across the capacitor at t = 8.0sec? A) 23.6 V B) 0.44 V C) 23.99 V D) 0.98 V

A) 23.6 V

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? 1. At the 0.75 m mark. 2. At the 0.5 m mark. 3. At either the 0 m or 1 m marks. 4. At the 0.35 m mark.

At the 0.5 m mark.

Units for charge?

C, coulombs

units for capacitance?

C/V, coulomb/volt or F; farad

units for current (I)?

C/s; coulombs/second or A; amperes

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

False

The only way for an object to have an electric charge is to have an excess of electrons. 1. True 2. False

False

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

False

unit for electrical potential difference?

J/C joule/coulomb or V, volt

Units for electrical field?

N/C, newtons/coulombs

If the amount of charge is fixed, a capacitor can store more energy when the voltage is larger. True False

True

Kirchoff's loop theorem states that the sum of ALL potential differences (drops and sources) around a closed loop must be zero. True False

True

Negative charges, when allowed to move, go towards regions where the electric potential is high. True False

True

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

True

units for electrical field?

V/m; volts/meter

unit for power?

W; watt

What is the equivalent resistance if the following resistors were arranged as in Fig. 18.28? (R1=3.0 ohms, R2=3.0 ohms, R3=4.0 ohms, R4=4.0 ohms) Question options: a. 1.5 ohms b. 14 ohms c. 2.9 ohms d. 0.9 ohms

a. 1.5 ohms

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? Question options: a. current in resistor 1=0.33 A, current in resistor 2=0.33 A, current in resistor 3=0.33 A. b. current in resistor 1=3.5 A, current in resistor 2=3.5 A, current in resistor 3=3.5 A c. current in resistor 1=1.6 A, current in resistor 2=1.3 A, current in resistor 3=0.6 A d. current in resistor 1=1.6 A, current in resistor 2=1.6 A, current in resistor 3=1.6 A

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

We can conserve energy by (choose all answers that are correct 1. using lightbulbs that use less electrical power while producing the same amount of light. 2. increasing the efficiency of all of our appliances and electrical devices. 3. following Dad's advice to "turn off the light when you're not in the room". 4. choosing appliances that minimize power consumption.

all of them

Electric fields are vector quantities. Which of the following descriptions is correct? a) The sign of the charge has nothing to do with the field direction. b) Positive charges have electric field vectors that point AWAY FROM the charge. c) Positive charges have electric field vectors that point TOWARDS the charge d) Negative charges have electric field vectors that point AWAY FROM the charge

b) Positive charges have electric field vectors that point AWAY FROM the charge.

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? a) The electric field in the metal of the cup is zero, the charge in the metal is -Q, and there is no surface charge. b) The electric field in the metal of the cup is zero, the charge in the metal is zero, and the surface charge is +Q c) The electric field in the metal of the cup is defined by -Q, the charge in the metal is +Q, and there is no surface charge. Correct Answer d) The electric field in the metal of the cup is zero, the charge in the metal is zero, and the surface charge is -Q. e) The electric field in the metal of the cup is defined by +Q, the charge in the metal is -Q, and there is no surface charge.

b) The electric field in the metal of the cup is zero, the charge in the metal is zero, and the surface charge is +Q

How are electric potential difference (voltage) and electric potential energy related? a) The voltage is the electric field value divided by a positive charge. b) The voltage is the potential energy per unit positive charge. c) The potential energy is the voltage per unit positive charge. d) There is no relationship.

b) The voltage is the potential energy per unit positive charge.

An electron volt measures a) electric potential difference. b) equipotential. c) energy. d) electric field.

c) energy.

An equipotential surface is a) always perpendicular to a charge distribution. b) the same as the direction of the electric field. c) the amount of work done in moving a charge. d) the set of locations where the electric potential is constant.

d) the set of locations where the electric potential is constant.

Which of the following is the correct loop equation starting from the tail of loop 1? Question options: a. -V1 - I1R1 - I2R2 + V2 = 0 b. V1 - I1R1 + I2R2 - V2 = 0 c. I1 + I2 = I3 d. -V1 - I1R1 + I2R2 + V2 = 0

d. -V1 - I1R1 + I2R2 + V2 = 0

Electric field lines are drawn parallel to equipotentials. True False

false

unit for Resistivity?

Ω x m; ohms times m

Units for resistance?

Ω, ohms