Physics Final Conceptual

A resistor and an inductor are connected in series to a battery. The battery is suddenly removed from the circuit. The time constant for of the circuit represents the time required for the current to decrease to 50% of the original value. 37% of the original value. 25% of the original value. 75% of the original value. 63% of the original value.

37% of the original value

A resistor and an inductor are connected in series to a battery. The time constant for the circuit represents the time required for the current to reach 75% of the maximum current. 37% of the maximum current. 63% of the maximum current. 50% of the original value. 25% of the maximum current.

63% of the maximum current

A constant magnetic flux through a closed loop of wire induces an emf in that loop. True False

False

An emf is induced in a wire by keeping a stationary magnet near the wire. True False

False

Faraday's law of induction and Lenz's law are actually the same law stated differently. True False

False

T or F Ampère's law can be used to find the magnetic field at the center of a circle formed by a current-carrying conductor.

False

T or F Ampère's law can be used to find the magnetic field at the center of a square loop carrying a constant current.

False

T or F The field near a long straight wire carrying a current is inversely proportional to the current flowing through the wire.

False

T or F The magnetic field near a current carrying wire is directly proportional to the distance from the wire.

False

T or F The magnitude of the magnetic field inside a solenoid is inversely proportional to the current flowing through the solenoid.

False

T or F If two identical wires carrying a certain current in the same direction are placed parallel to each other, they will experience a force of repulsion.

False

You are looking straight down on a magnetic compass that is lying flat on a table. A wire is stretched horizontally under the table, parallel to and a short distance below the compass needle. The wire is then connected to a battery so that a current I flows through the wire. This current causes the north pole of the compass needle to deflect to the left. The questions that follow ask you to compare the effects of different actions on this initial deflection. With the wire back at its initial location, you connect a second identical battery in series with the first one. When you close the switch, how does the new angle of deflection of the north pole of the compass needle compare to its initial deflection?

It is larger

You are looking straight down on a magnetic compass that is lying flat on a table. A wire is stretched horizontally under the table, parallel to and a short distance below the compass needle. The wire is then connected to a battery so that a current I flows through the wire. This current causes the north pole of the compass needle to deflect to the left. The questions that follow ask you to compare the effects of different actions on this initial deflection. If the wire is lowered farther from the compass, how does the new angle of deflection of the north pole of the compass needle compare to its initial deflection?

It is smaller

Comparing the mutual inductance M12 of coil 1 with respect to coil 2 with the mutual inductance M21 of coil 2 with respect to coil 1, it turns out that M12 > M21. M12 is always greater. M21 is always greater. M12 < or = M21. M12 = M21.

M12 = M21.

What physical property does the symbol Iencl represent? The current along the path in the same direction as the magnetic field The current in the path in the opposite direction from the magnetic field The total current passing through the loop in either direction The net current through the loop

The net current through the loop

Starting from zero, an electric current is established in a circuit made of a battery of emf E, a resistor of resistance R and an inductor of inductance L. The electric current eventually reaches its steady-state value. What would be the effect of using an inductor with a larger inductance in this circuit? The steady-state value of the current would be the same, but it would take the same amount of time to reach it. The steady-state value of the current would be the same, but it would take less time to reach it. The steady-state value of the current would be larger, but it would take more time to reach it. The steady-state value of the current would be larger, but it would take the same amount of time to reach it. The steady-state value of the current would be the same, but it would take more time to reach it.

The steady-state value of the current would be the same, but it would take more time to reach it.

A changing magnetic field can produce an electric current. True False

True

A changing magnetic flux through a closed loop of wire induces an emf in that loop. True False

True

A constant magnetic field can be used to produce an electric current. True False

True

According to Lenz's Law, the direction of the induced current in a conducting loop of wire is that which tends to oppose the change that produces it. True False

True

An emf is induced in a wire by changing the current in that wire. True False

True

An emf is induced in a wire by moving the wire near a magnet. True False

True

If the minus sign were not in Faraday's law it would lead to a violation of the law of conservation of energy. True False

True

T or F Ampère's law can be used to find the magnetic field around a straight current-carrying wire.

True

The emf in a conducting rod of length L moving perpendicular to a magnetic field is directly proportional to the speed of the rod. True False

True

The field outside a solenoid behaves like that of a bar magnet. True False

True

The negative sign in the Faraday's equation for electromagnetic induction is related to the direction of the induced emf. True False

True

T or F Ampère's law can be used to find the magnetic field inside a toroid. (A toroid is a doughnut shape wound uniformly with many turns of wire.)

Ture

Which of the following choices of path allow you to use Ampère's law to find vector B(r)? a) The path must pass through the point r . b) The path must have enough symmetry so that B(r)*dl is constant along large parts of it. c) The path must be a circle.

a and b

Magnetic flux depends upon the magnetic field. the area involved. the orientation of the area with respect to the field. all of the above none of the above

all of the above

Mutual inductance can depend upon the number of coils. the number of turns. the relative position of the coils. the shape of the coils. all of the above as well as other factors.

all the above

The circle on the integral means that Vector B(r) must be integrated over a circle or a sphere. along any closed path that you choose. along the path of a closed physical conductor. over the surface bounded by the current-carrying wire

along any closed path that you choose

In using Ampere's law, the integral must be evaluated in a counter-clockwise direction. around a closed path. around a path that lies in a plane. in a clockwise direction. around a circular path.

around a closed path

If the current increases in a solenoid, the induced emf acts to increase the flux. decrease the flux. first increase then decrease the flux. first decrease then increase the flux. have no effect on the flux.

decrease flux

In ferromagnetic materials the small regions that act like tiny magnets are called spins. domains. conductors. iron filings. ferromagnets.

domains

A resistor and an inductor are connected in series to an ideal battery of constant terminal voltage. At the moment contact is made with the battery, the voltage across the inductor is greater than the battery's terminal voltage. equal to the battery's terminal voltage. less than the battery's terminal voltage, but not zero. zero.

equal to the batteries terminal voltage

Two long parallel wires placed side-by-side on a horizontal table carry identical current straight toward you. From your point of view, the magnetic field at the point exactly between the two wires points away from you. points down. points up. is zero. points toward you.

is zero

Two long parallel wires placed side-by-side on a horizontal table carry identical size currents in opposite directions. The wire on your right carries current toward you, and the wire on your left carries current away from you. From your point of view, the magnetic field at the point exactly midway between the two wires points up. points toward you. points down. is zero. points away from you.

points down

The magnetic field produced by a long straight current-carrying wire is inversely proportional to the current in the wire and proportional to the distance from the wire. proportional to the current in the wire and inversely proportional to the distance from the wire. inversely proportional to both the current in the wire and the distance from the wire. independent of both the current in the wire and the distance from the wire. proportional to both the current in the wire and the distance from the wire

proportional to the current in the wire and inversely proportional to the distance from the wire.

To understand Ampère's law and its application. The integral on the left is the integral throughout the chosen volume. the surface integral over the open surface. the surface integral over the closed surface bounded by the loop. the line integral along the closed loop the line integral from start to finish.

the line integral along the closed loop.

Two long parallel wires are placed side-by-side on a horizontal table. If the wires carry current in the same direction, both wires are forced against the table's surface. the wires repel each other. both wires are lifted slightly. one wire is lifted slightly as the other wire is forced against the table's surface. the wires attract each other.

the wires attract each other

The ampere is defined as 4π × 10-5 SI units. as a coulomb-second. as 4π × 10-7 SI units. as a coulomb/second2. using the force between current carrying wires.

using the force between current carrying wires

A resistor and an inductor are connected in series to an ideal battery of constant terminal voltage. At the moment contact is made with the battery, the voltage across the resistor is less than the battery's terminal voltage, but not zero. greater than the battery's terminal voltage. zero. equal to the battery's terminal voltage.

zero