Physics 104 Final

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

d

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

You can increase the strength of a solenoid's magnetic field by inserting an iron core inside the coils of the solenoid. True/False

false

Two point charges, the first with a charge of +4.47 x 10-6 C and the second with a charge of +1.86 x 10-6C, are separated by 17.4 mm. What is the magnitude of the electrostatic force experienced by charge 2? a) 247 N b) 2.47 x 10-4 N c) 103 N d) 2.74 x 10-8 N

a

What is the equivalent resistance in the following arrangement of resistors? (R1=3.0 ohms, R2=3.0 ohms, R3=4.0 ohms, R4=4.0 ohms) a) 1.5 ohms b) 14 ohms c) 2.9 ohms d) 0.9 ohms

a

What is the magnitude of the magnetic force exerted on a 4.67-m length of wire carrying a current of 2.38 A perpendicular to a magnetic field of 0.385 T? a) 4.28 N b) 0.916 N c) 11.1 N d) 1.80 N

a

In order to measure the voltage drop due to a resistor in a circuit, a voltmeter should be: a) connected only to the wire through which the current leaves the resistor. b) connected in series, or "in-line", with the resistor. c) connected in parallel, or "across", the resistor. d) connected to the battery or voltage source

c)

An ideal ammeter has a voltage drop across it. True/False

False

A step-up transformer increases voltage while at the same time decreasing the current true/false

true

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

true

The magnetic field due to an induced current points in a direction opposite to the direction of the field that caused the induced current. True/False

true

The net force on a current-carrying loop in a uniform magnetic field is zero. True/False

true

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

true

A 100-W lightbulb operates on a potential difference of 120 V. Find the resistance of the bulb. a) 144 Ω b) 12 Ω c) 120 Ω d) 0.007 Ω

a

A 8.45-μC particle with a mass of 6.15 x 10-5 kg moves perpendicular to a 0.493-T magnetic field in a circular path of radius 34.1 m. How much time will it take for the particle to complete one orbit? a) 92.7 s b) 0.0927 s c) 9.27 s d) 927 s

a

A 9.0-V battery is connected across the terminals A and B for the group of resistors shown in the figure. What is the potential difference across R2? a) 3.6 V b) 9.0 V c) 5.4 V d) 1.8 V

a

A cell membrane is 8.7 nm thick and has an electrical resistivity of 1.3 x 107 Ωm. If the potential difference between the inner and outer surfaces of a cell membrane is 63 mV, how much current flows through a circular patch of membrane with radius 1.0 μm? a) 1.8 x 10-12 A b) 5.6 x 10-13 A c) 1.3 x 10-5 A d) 1.2 x 10-18 A

a

A charge of +3q sits at the origin. A charge of -5q sits on the x-axis at the 1.00 m mark. Given that q=4.11 x 10-9 C, at what location on the x-axis is the electric potential zero? a) 0.375 m b) 0.500 m c) 0.625 m d) 0.125 m

a

A circular coil of wire has a radius of 6.30 cm and has 215 turns of wire that carries 5.90 A of current. What is the magnetic field at the center of the coil? a) 12.7 mT b) 6.33 mT c) 58.8 μT d) 1 x 104 T

a

A parallel plate capacitor has plates with an area of 0.019 m2 and a separation of 0.72 mm. The space between the plates is filled with a dielectric whose dielectric constant is 2.4. What is the potential difference between the plates when the charge on the capacitor plates is 5.8 μC? a) 1.0 x 104 V b) 1.0 x 10-4 V c) 2.4 x 104 V d) 1.0 x 107 V

a

A portable CD player operates with a current of 20 mA at a potential difference of 6.2 V. What is the power usage of the player? a) 0.124 W b) 124 W c) 12.4 W d) 0.124 V e) 1.24 V

a

A proton has an initial speed of 4.90 x 105 m/s. What potential difference is required to bring the proton to rest? a) 1250 V b) -1250 V c) 2.00 x 10-16 V d) -2.00 x 10-16 V e) zero

a

A single conducting loop of wire has an area of 4.8 x 10-2 m2 and a resistance of 97 Ω. Perpendicular to the plane of the loop is a magnetic filed of strength 1.1 T. At what rate must this field change if the induced current in the loop is to be 0.64 A? a) 1300 T/s b) 2.7 x 104 T/s c) 62 T/s d) 660 T/s

a

A system of 1728 particles, each of which is either an electron or a proton, has a net charge of +3.552 x 10-17 C. What is the mass of this system? a) 1.629 x 10-24 kg b) 222.0 kg c) 1.574 x 10-27 kg d) 2.886 x 10-24 kg

a

An aluminum wire is 1.3 m long and has a diameter of 0.05 cm. What is the resistance of the wire? a) 0.18 Ω b) 0.045 Ω c)9.0 x 10-5 Ω d) 2.65 x 10-8 Ω e) 5.3 x 10-5 Ω

a

An electrically neutral object (like a balloon) a) can be subjected to electric forces due to polarization. b) cannot be subjected to electric forces because it is neutral. c) can be subjected to electric forces only if it gains a net negative charge. d) can be subjected to electric forces only if it gains a net positive charge.

a

An object with a charge of +6.3 μC and a mass of 0.073 kg experiences an upward electric force, due to a uniform electric field, equal in magnitude to its weight. If the electric charge on the object is reduced by a factor of one-third while its mass remains the same, find the direction and magnitude of its acceleration. a) down at 6.5 m/s2 b) up at 4.9 m/s2 c) up at 9.8 m/s2 d) down at 4.9 m/s2 e) up at 6.5 m/s2 f) down at 9.8 m/s2

a

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

a

Consider the long, straight current-carrying wires shown in the figure. One wire carries a current I1 = 4.5 A in the positive x-direction; the other wire carries a current I2 = 3.2 A in the negative y-direction. Calculate the net magnetic field at point A. a)15 μT, into the page (-z-hat) b) 15 μT, out of the page (+z-hat) c) 2.6 μT, into the page (-z-hat) d) 2.6 μT, out of the page (+z-hat)

a

The resistance of something a) depends on its resistivity and its geometry. b) depends only on its geometry. c) depends only on its resistivity. d) is a fundamental property of a material.

a

The resistor in an RC circuit has a resistance of 110 Ωand a time constant of 1.9 ms. Calculate the current in the circuit 7.6 ms after the switch is closed. Assume that the capacitor is initially uncharged and that the emf of the battery is 12.0 V. a) 2 mA b) 110 mA c) 27.5 mA d) 40 mA

a

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, a) then the force on both charges increases by a factor of 2. b) then the force doesn't change because the objects are fixed. c) only the force on the positive charge increases by a factor of 2. d) only the force on the negative charge increases by a factor of 2.

a

Two point charges lie on the x axis. A charge of -2.3 x 10-6 C is at x=-5 cm, and a charge of +9.2 x 10-6 C is at x=12 cm. At what position x would a third positive charge be in equilibrium? a) x=-22 cm b) x=+22 cm c) x=0 cm d) x=-17 cm e) x=+17 cm

a

A proton travels at a speed of 3.0x10^(6) m/s through a uniform magnetic field whose magnitude is 8.0x10^(-3) T. What is the magnitude of the magnetic force on the proton if its velocity vector and the magnetic field vector are perpendicular? a) 3.8x10^(-15) N b) 3.8x10^(-18) N c) 0.0 N d) 3.8x10^(-15

a)

A solenoid with 300 turns per centimeter has an iron core with a relative permeability of 100. The solenoid carries a current of 5.0 A. What is the magnetic field at the central axis of the solenoid? 19 T 0.19 T 1.9 T 30 T

a)

An emergency AC generator operates at a rotation frequency of 120 Hz. If the output voltage is zero at t=0, when is it next zero? a) 4.17x10^(-3) s b) 8.33x10^(-3) s c) 1.67x10^(-2) s d) 3.13x10^(-3) s

a)

During one cycle, the average AC voltage is a) zero. b) the maximum voltage minus the minimum voltage. c) the maximum voltage. d) one-half the maximum voltage.

a)

In a motor, back EMF increases as a) the armature loop increases its angular speed. b) the armature loop decreases its angular speed. c) the external magnetic field gets stronger. d) the current in the loop increases.

a)

The electric and magnetic fields that make up a light wave a) reach maximum values at the same time but oscillate in perpendicular directions. b) reach maximum values at different times and oscillate in the same direction. c) reach maximum values at the same time and oscillate in the same direction. d) reach maximum values at different times but oscillate in perpendicular directions.

a)

The speed of an electromagnetic wave a) is constant. b)is different for different frequencies. c) is different for different wavelengths. d) depends on what creates it.

a)

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

c

If the distance between two equal positive charges doubles, a) the magnitude of the electric force increases by a factor of 4. b) the magnitude of the electric force does not change. c) the magnitude of the electric force decreases by a factor of 4. d) the magnitude of the electric force decreases by a factor of 2.

c

If you are charging an initially uncharged capacitor in an RC circuit, the voltage of the capacitor a) starts at the battery voltage and decreases to zero. b) always remains equal to the battery voltage. c) starts at zero and increases to the battery voltage. d) remains at zero always.

c

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

c

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

c

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? a) The magnitude of charge B is 4 times as large as charge A. b) The magnitude of charge A is 4 times as large as charge B. c) The magnitude of charge B is twice as large as charge A. d) The magnitude of charge A is twice as large as charge B.

c

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

c

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

c

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

c

You rub a balloon on your hair and it gains a net negative charge. Which of the following statements is true? a) 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. b) The charge gained by the balloon was created by friction, so the net change in the charge of the hair-balloon system is negative. c) 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. d) The charge gained by the balloon was created by induction, so the net change in the charge of the hair-balloon system is negative.

c

By convention, magnetic field lines: a) can either enter or exit N poles and S poles. b) enter at N poles and exit from S poles. c) exit from N poles and enter at S poles. d) don't tell us anything about the direction of magnetic fields.

c)

The magnetic flux through a loop of wire is maximum a) when the magnetic field direction is parallel to the plane of the loop. b) when the magnetic field direction is 45-degrees from the plane of the loop. c) when the magnetic field direction is perpendicular to the plane of the loop. d) independent of the orientation of the magnetic field and loop.

c)

The magnetic force on a current-carrying wire is greatest when the current is: a)due to positive charges only. b) at a 45-degree angle to the magnetic field direction. c) perpendicular to the magnetic field direction. d) parallel to the magnetic field direction.

c)

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? a) 1.25 ohms b) 75 ohms c) 60 ohms d) 48 ohms

d

Capacitance increases as a) the charge increases and/or the voltage increases. b) the charge decreases and/or the voltage decreases. c) the charge decreases and/or the voltage increases. d) the charge increases and/or the voltage decreases.

d

For resistors in parallel, a) the current only flows through one resistor. b) the individual voltage drops across the resistors add up to the total voltage. c) the currents through each resistor are equal. d) the voltages across each resistor are equal.

d

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? a) The electric forces in set A are repulsive, but the forces in set B are attractive. b) The electric forces in both cases are attractive. c) The electric forces in set A are attractive, but the forces in set B are repulsive. d) The electric forces in both cases are repulsive

d

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. a) 15 million ohms b) 10 million ohms c) 5 million ohms d) 2.5 million ohms

d

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? a) $12.60 b) $0.90 c) $40.50 d)$18.90

d

During any complete cycle in which the initial EMF is zero, the EMF of an AC generator becomes zero again at a) a time equal to one-quarter of the total period. b) no time ever. c) a time equal to three-quarters of the total period. d) a time equal to one-half of the total period.

d)

Ohm's law can be applied to AC circuits a)if the resistance used is an rms value. b) as long as you use the average voltage c) no matter what voltage and current values you use. d) if the voltage and current used are rms values.

d)

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

false

If the maximum AC current increases to a new value that is twice as large as the original value, the new root-mean-square (rms) current also increases by a factor of 2 over the original value. true/false

false

In reality, magnetic poles can be found as isolated, single objects. True/false

false

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

false

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

false

Visible light is the only really useful type of electromagnetic radiation. true/false

false

Electromagnetic radiation is caused by a) magnets in motion. b) accelerating electric charges. c) electric charges in motion. d) nuclear reactions.

b)

If a loop of wire is stretched in a direction perpendicular to the direction of a constant, uniform magnetic field, then no induced current will run through the loop because the magnetic field is constant. a) then no induced current will run through the loop because the magnetic field is constant. b) then an induced current will run through the loop because the loop encloses a varying number of magnetic field lines. c) then an induced current will run through the loop because the magnetic field is constant. d) then no induced current will run through the loop because the loop encloses a varying number of magnetic field lines.

b)

In a laboratory, two wires lay next to each other on a bench. Wire A is twice as long as wire B. An experiment causes the two wires to have the same current flowing through them. The wires both exist in the magnetic field of the Earth. Which of the following correctly describes the magnetic force magnitudes experienced by the wires? a) Wire B feels twice the force of wire A. b) Wire A feels twice the force of wire B. c) The wires feel the same force

b)

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

b)

The torque on a current-carrying loop is maximum when: a) the magnetic moment is zero: b) the magnetic moment is perpendicular to the magnetic field direction. c) the magnetic moment points in the direction of the current. d) the magnetic moment is along the magnetic field direction.

b)

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 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 c) The electric field in the metal of the cup is zero, the charge in the metal is zero, and the surface charge is -Q. d) The electric field in the metal of the cup is zero, the charge in the metal is -Q, and there is no surface charge. 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, c

The magnetic field at the center of a current carrying loop (choose ALL answers that apply) a) points towards the center of the loop. b) increases in magnitude as the current increases. c) increases in magnitude as the radius of the loop increases. d) points in a direction perpendicular to the plane that contains the loop.

b, d

A 12-V battery is connected to four capacitors in series. The capacitors have the following capacitances: 9 μF, 12 μF, 32 μF, and 42 μF. Find the voltage across the 32 μF capacitor. a) 4 V b) 12 V c) 1.5 V d) 0.375 V

c

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? a) 100 V b) 75 V c) 200 V d) 1600 V

c

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? a) 0.83 b) 1.7 c) 1.2 d) 1.0

c

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

c

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

c

As the current increases, the electric power provided by a battery a) decreases. b) stays the same. c) increases. d) decreases first, then increases.

c

Compared to solenoid B, solenoid A has ten times the number of turns per meter. The largest magnetic field belongs to a) solenoid B. b) neither, they are both zero. c) solenoid A. d) neither, they are the same.

c

When resistors are connected in parallel, the currents through each resistor a) are different with the largest current flowing through the largest resistor. b) are different with the largest current flowing through the smallest resistor. c) are zero in all resistors but one. d) are all equal.

b

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

b

A square loop of wire that encloses an area of 0.20 m^2 is in a uniform magnetic field of 0.10 T. What is the flux through the loop if its plane is at an angle of 62 degrees to the field? a) 9.4x10^(-3) b) 1.8x10^(-2) Wb c) 2.0x10^(-2) Wb d) 9.4x10^(-3) Wb

b)

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

a, b, c, d

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

a, c

The direction of the magnetic force exerted on a charged object is ALWAYS (choose ALL that apply) a) perpendicular to the velocity vector (direction of motion). b) along the magnetic field vector (field direction). c) perpendicular to the magnetic field vector (field direction). d) along the velocity vector (direction of motion). e) in a direction that makes the velocity and field vectors align.

a,c

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

b

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? a) No charge b) -Q c) +Q

b

Electric potential is a) the same as electic field. b) a scalar. c) a vector. d) the same as electric force.

b

Find the current in resistor R3. a) 3.75 A b) 1.25 A c) 5.00 A d) 2.50 A

b

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

b

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

b

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? a) 2 N/C. b) 8 N/C. c) 4 N/C. d) 0.5 N/C.

b

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, a) the total voltage available to the dead car is twice as large as that of the good battery. b) the total voltage available to the dead car is the same as that of the good battery. c) the total voltage available to the dead car is half that of the good battery. d) the total voltage available to the dead car is 4 times as large as that of the good battery.

b

Kirchoff's junction theorem is a restatement of which of the following physical laws? a) Conservation of momentum. b) Conservation of charge. c) Conservation of energy. d) Conservation of mass.

b

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? a) The work done by the electric field as the charge moves is zero. b) The work done by the electric field as the charge moves is +qEd. c) The work done by the electric field as the charge moves is -qEd.

b

What is the voltage across ten 2.0 V batteries when they are connected in parallel? a) 20 V b) 2.0 V c) 5.0 V d) 10 V

b

An AC circuit with a resistance of 10-ohms has an effective current of 3.0 A. Find the peak voltage. a) 42.4 b) Correct! 42.4 V c) 30 V d) 0.3 V

b)