Quiz 6

If the currents in these wires have the same magnitude, but opposite directions, what is the direction of the magnetic field at point P?

3) direction 3 Using the right-hand rule, we can sketch the B fields due to the two currents. Adding them up as vectors gives a total magnetic field pointing downward.

A wire loop is being pulled through a uniform magnetic field. What is the direction of the induced current?

3) no induced current Since the magnetic field is uniform, the magnetic flux through the loop is not changing. Thus no current is induced.

As increase the number of branches in parallel circuit, the overall current in the power source a- stays the same b- increases c- decreases

B

A light bulb uses 30 W when connected to 3 V battery. If it is connected to a 6 V battery it will use a. 90 W b. 30 W c. 120 W d. 60 W e. 150 W

C

A battery charges a parallel-plate capacitor fully and then is removed. The plates are then slowly pulled apart. What happens to the potential difference between the plates as they are being separated? a. It decreases. b. It remains constant. c. It cannot be determined from the information given. d. It increases.

D

A kilowatt hour is a unit of a. current b. energy per charge (voltage) c. resistance to the flow of electricity d. energy e. power

D

A parallel-plate capacitor is connected to a battery and becomes fully charged. The capacitor is then disconnected, and the separation between the plates is increased in such a way that no charge leaks off. As the plates are being separated, the energy stored in this capacitor a. does not change. b. decreases. c. become zero. d. increases.

D

The energy stored in a capacitor is directly proportional to a. the charge on the capacitor. b. the voltage across the capacitor. c. the reciprocal of the charge on the capacitor. d. Both voltage and charge e. the square of the voltage across the capacitor.

D

When a 10 V battery is connected to a resister, the current in the resistor is 2 A. What is the resistor's value? a- more than 20 ohms b- 10 ohms c- 20 ohms d- 5 ohms e- 2 ohms

D

When we say an appliance "uses up electricity," we are really saying that a- main power supply voltage is lowered b- electrons are removed from the circuit and placed elsewhere c- current disappears d- electron kinetic energy is changed to heat e- electric charges are lost

D

As more lights are connected in parallel Select one: a. overall current flowing from the battery increases and the battery drains faster. b. the lights are at their brightest and do not change. c. the electric potential of the power supply is unchanged. d. overall resistance decreases. e. All of these.

E

Four identical resistors are connected in parallel. Each is a quarter ohm resistor. What is the equivalent resistance of these resisters? a. 1/4 of an ohm b. 4 ohms c. none of the above d. 1 ohm e. 1/16 of an ohm

E

Three identical light bulbs are connected in series with an overall voltage of 3 V. The light bulbs are shining dimly. Which of the following is true regarding these light bulbs? a. Each light bulb receives about 3 V b. Each light bulb receives about 1 V c. Each light bulb receives about 9 V d. Each light bulb receives the same current e. Two of these statements are true

E

In a dc circuit, the inductive effect starts once the current reaches the value defined by Ohm's law and remains constant. a)true b)false

False

Which resistor has the greatest current going through it? Assume that all the resistors are equal.

R5 The same current must flow through left and right combinations of resistors. On the LEFT, the current splits equally, so I1 = I2. On the RIGHT, more current will go through R5 than R3 + R4 since the branch containing R5 has less resistance

In the circuit below, what is the current through R1?

d) 2 A The voltage is the same (10 V) across each resistor because they are in parallel. Thus, we can use Ohm's law, ΔV1 = I1R1 to find the current I1 = 2 A.

The lightbulbs in the circuits below are identical with the same resistance R. Which circuit produces more light? (brightness power)

a) circuit I In circuit I, the bulbs are in parallel, lowering the total resistance of the circuit. Thus, circuit I will draw a higher current, which leads to more light, because P = IΔV.

Two lightbulbs A and B are connected in series to a constant voltage source. When a wire is connected across B, bulb A will:

a) glow brighter than before Since bulb B is bypassed by the wire, the total resistance of the circuit decreases. This means that the current through bulb A increases.

Points P and Q are connected to a battery of fixed voltage. As more resistors R are added to the parallel circuit, what happens to the total current in the circuit?

a) increases As we add parallel resistors, the overall resistance of the circuit drops. Since ΔV = IR, and ΔV is held constant by the battery, when resistance decreases, the current must increase.

How does the voltage V1 across the first capacitor (C1) compare to the voltage V2 across the second capacitor (C2)?

b) V1 > V2 The voltage across C1 is 10 V. The combined capacitors C2 + C3 are parallel to C1. The voltage across C2 + C3 is also 10 V. Since C2 and C3 are in series, their voltages add. Thus the voltage across C2 and C3 each has to be 5 V, which is less than V1.

Current flows through a lightbulb. If a wire is now connected across the bulb, what happens?

c) all the current flows through the wire The current divides based on the ratio of the resistances. If one of the resistances is zero, then ALL of the current will flow through that path Two lightbulbs A and B are

An ammeter A is connected between points a and b in the circuit below, in which the four resistors are identical. The current through the ammeter is:

e) zero Since all resistors are identical, the voltage drops are the same across the upper branch and the lower branch. Thus, the potentials at points a and b are also the same. Therefore, no current flows.

A horizontal wire carries a current and is in a vertical magnetic field. What is the direction of the force on the wire?

5) out of the page Using the right-hand rule, we see that the magnetic force must point out of the page. Since F must be perpendicular to both I and B, you should realize that F cannot be in the plane of the page at all.

The length of time required for the current to decay to zero, once the circuit is de-energized, equals the time required for the current to rise to its Ohm's law value when the inductive circuit is energized. a)true b)false

A

A dielectric material such as paper is inserted between the plates of a capacitor as the capacitor holds a fixed charge on its plates. What happens to the electric field between the plates as the dielectric is inserted? a. The field reduces to zero. b. The field becomes weaker. c. The field becomes stronger. d. There is no change in the field.

B

Current is measured by placing the red plug into which port: a. Any port (they're all the same) b. 10 ADC c. COM (only this port!) d. V

B

The relationship between current and potential in Ohm's Law is a. Neither of these. b. directly proportional. c. inversely proportional.

B

Two D cell batteries are placed in parallel in the circuit. How much voltage do the batteries provide to the circuit? a. 6 V b. 1.5 V c. 0.75 V d. 3 V

B

Two capacitors, one 0.1F and one 0.2F are connected together in series and are charged by the 9V battery. What's true about the voltage of these caps? a. the 0.1 F cap has 4.5 V while the 0.2 F cap has 4.5 V b. the 0.1 F cap has 6 V while the 0.2 F cap has 3 V c. the 0.1 F cap has 3 V while the 0.2 F cap has 6 V d. the 0.1 F cap has 0 V while the 0.2 F cap has 9 V

B

What color wire do you always plug into the COM port? a. Blue b. Black c. Red

B

What happens to the current in a circuit when the voltage decreases? a. The current increases b. The current decreases

B

Why do the caps eventually stop charging up? a. the current from the capacitor is opposite of the current from the batter so their is no net current b. the voltages of the two caps eventually opposes the voltage of any charge coming out of the battery c. the caps eventually fill up and can't receive any more charge d. the voltage of the 1st cap is the same as the battery so no current is possible

B

When resistors are connected in parallel, we can be certain that A) the same current flows in each one. B) the potential difference across each is the same. C) the power dissipated in each is the same. D) their equivalent resistance is greater than the resistance of any one of the individual resistances.

B) the potential difference across each is the same.

An ideal parallel-plate capacitor has a capacitance of C. If the area of the plates is doubled and the distance between the plates is halved, what is the new capacitance? Select one: a. 2C b. C/4 c. C/2 d. 4C

D

When two or more resistors are connected in parallel to a battery, A) the voltage across each resistor is the same. B) the total current flowing from the battery equals the sum of the currents flowing through each resistor. C) the equivalent resistance of the combination is less than the resistance of any one of the resistors. D) all of the given answers

D) all of the given answers.

You double the voltage across a certain conductor and you observe the current increases three times. What can you conclude

Ohm's law is not obeyed Ohm's law, V = IR, states that the relationship between voltage and current is linear. Thus, for a conductor that obeys Ohm's law, the current must double when you double the voltage

If there is a current in the loop in the direction shown, the loop will:

3) rotate clockwise Look at the north pole: here the magnetic field points to the right and the current points out of the page. The right-hand rule says that the force must point up. At the south pole, the same logic leads to a downward force. Thus the loop rotates clockwise

If there is induced current, doesn't that cost energy? Where would that energy come from in case 2?

3) there is less KE in case 2 In both cases, the magnet starts with the same initial gravitational PE. In case 1, all the gravitational PE has been converted into kinetic energy. In case 2, we know the magnet falls slower, thus there is less KE. The difference in energy goes into making the induced current.

A rectangular current loop is in a uniform magnetic field. What is the direction of the net force on the loop?

3) zero Using the right-hand rule, we find that each of the four wire segments will experience a force outward from the center of the loop. Thus, the forces of the opposing segments cancel, so the net force is zero

A horizontal wire carries a current and is in a vertical magnetic field. What is the direction of the force on the wire?

3) zero current is parallel to magnetic field lines

Doubling the capacitance of a capacitor that is holding a constant charge causes the energy stored in that capacitor to a. decrease to one-fourth. b. quadruple. c. decrease to one-half. d. double.

C

How does voltage in Ohm's Law affect resistance? a. inversely proportional. b. directly proportional. c. no direct affect

C

Kirchhoff's junction rule states that the a. charge entering a junction equals the charge leaving a junction and implies that current adds in series. b. potential entering a junction equals the potential leaving a junction and implies that current stays the same in parallel. c. charge entering a junction equals the charge leaving a junction and implies that current adds in parallel. d. charge entering a junction equals the charge leaving a junction and implies that current stays the same in parallel. e. potential entering a junction equals the potential leaving a junction and implies that current adds in parallel.

C

Kirchhoff's loop rule states that the net a. current in any loop of a circuit equals zero, and implies that current adds in series. b. resistance in any loop of a circuit equals zero, and implies that resistance adds in series. c. potential in any loop of a circuit equals zero, and implies that potential adds in series. d. current in any loop of a circuit equals zero, and implies that current adds in parallel. e. potential in any loop of a circuit equals zero, and implies that potential adds in parallel

C

Which statement is correct? a- Current is the primary cause of voltage b- Resistance flows through an open circuit c- Charge flows in a closed circuit d- Voltage flows through an open or closed circuit

C

Which is the correct way to light the lightbulb with the battery?

C Current can flow only if there is a continuous connection from the negative terminal through the bulb to the positive terminal. This is the case for only Fig. (3).

A parallel-plate capacitor consists of a set of two parallel plates of area A separated by a distance d. This capacitor is connected to a battery that maintains a constant potential difference across the plates. A slab of a dielectric material is inserted in the region between the plates and completely fills it. What changes would you observe as the dielectric is inserted? (There could be more than one correct choice.) a. Only the capacitance would change. b. Only the charge on the plates of the capacitor would change. c. Nothing would change. d. The potential difference across the plates would increase. e. Both the charge on the plates of the capacitor and its capacitance would change.

E