physics 21 MCQ

Which of the following can a transformer accomplish? Changing both current and voltage. Changing power. Changing current but not voltage. Changing voltage but not current.

Changing both current and voltage. Changing power.

Which of the following will not induce a current in the loop? Moving the loop in a direction parallel to the wire. Increasing the current in the straight wire. Rotating the loop so that it becomes perpendicular to the plane of the figure. Moving the loop farther from the wire without rotating it. Moving the loop farther from the wire while rotating it.

Moving the loop in a direction parallel to the wire.

Which of the following will not increase a generator's voltage output? Check all that apply. Rotating the magnetic field so that it is more closely parallel to the generator's rotation axis. Increasing the area of the coil. Increasing the magnetic field through the coil. Increasing the number of turns in the coil. Rotating the generator faster.

Rotating the magnetic field so that it is more closely parallel to the generator's rotation axis.

When you swipe a credit card, the machine sometimes fails to read the card. What can you do differently? Swipe the card more slowly so that the magnetic fields don't change so fast. Swipe the card more quickly so that the induced currents are reduced. Swipe the card more slowly so that the reader has more time to read the magnetic stripe. Swipe the card more quickly so that the induced emf is higher.

Swipe the card more quickly so that the induced emf is higher.

Which of the following is true about all series ac circuits? Which of the following is true about all series ac circuits? The current at any point in the circuit is always the same as the current at any other point in the circuit. The voltage across any circuit element is a maximum when the current is a maximum in that circuit element. The current in the circuit is a maximum when the source ac voltage is a maximum. Resistors, capacitors, and inductors can all change the phase of the current.

The current at any point in the circuit is always the same as the current at any other point in the circuit. Current same at all points but out of phase.

A bar magnet is held above the floor and dropped. If there is induced current, wouldn't that cost energy? Where would that energy come from in case the magnet falls through a wire loop? (Figure 1) If there is induced current, wouldn't that cost energy? Where would that energy come from in case the magnet falls through a wire loop? Energy conservation is violated. Induced current doesn't need energy. There is less kinetic energy. There is more gravitational potential energy.

There is less kinetic energy.

Which of the following statements about transformers is false? If the current in the secondary is higher, the voltage is lower. If the voltage in the secondary is higher, the current is lower. Transformers work using ac current or dc current. If no flux is lost, the product of the voltage and the current is the same in the primary and secondary coils.

Transformers work using ac current or dc current. Only for AC

When a generator is used to produce electric current, the resulting electric energy originates from which source? When a generator is used to produce electric current, the resulting electric energy originates from which source? The generator's magnetic field. The resistance of the generator's coil. Back emf. Whatever rotates the generator's axle. Empty space.

Whatever rotates the generator's axle.

The alternating electric current at a wall outlet is most commonly produced by The alternating electric current at a wall outlet is most commonly produced by using an electric motor. a connection to rechargeable batteries. alternately heating and cooling a wire. accelerating electrons between oppositely charged capacitor plates. a rotating coil that is immersed in a magnetic field.

a rotating coil that is immersed in a magnetic field.

A nonconducting plastic hoop is held in a magnetic field that points out of the figure (Figure 1) . As the strength of the field increases, A nonconducting plastic hoop is held in a magnetic field that points out of the figure . As the strength of the field increases, an induced emf will be produced but no current. no induced emf will be produced. an induced emf will be produced that causes a counterclockwise current. an induced emf will be produced that causes a clockwise current.

an induced emf will be produced but no current.

A square loop moves to the right from an area where B⃗ =0, completely through a region containing a uniform magnetic field directed into the figure (Figure 1) , and then out to B=0 after point L. A current is induced in the loop A square loop moves to the right from an area where , completely through a region containing a uniform magnetic field directed into the figure , and then out to after point . A current is induced in the loop as it passes line J or line L. only as it passes line J. only as it passes line L. only as it passes line K. as it passes all three lines.

as it passes line J or line L. current induced when there is a change in magnetic flux

Two separate but nearby coils are mounted along the same axis. A power supply controls the flow of current in the first coil, and thus the magnetic field it produces. The second coil is connected only to an ammeter. The ammeter will indicate that a current is flowing in the second coil only when the current in the first coil changes. whenever a current flows in the first coil. only when a steady current flows in the first coil. only if the second coil is connected to the power supply by rewiring it to be in series with the first coil.

only when the current in the first coil changes.

A laptop computer's charger unit converts 120 V from a wall power outlet to the lower voltage required by the laptop. Inside the charger's plastic case is a diode or rectifier that changes ac to dc plus a A laptop computer's charger unit converts 120 from a wall power outlet to the lower voltage required by the laptop. Inside the charger's plastic case is a diode or rectifier that changes ac to dc plus a motor. transmission line. generator. transformer. battery.

transformer.

A loop rests in the plane of a page of textbook while a magnetic field is directed into the page. A clockwise current is induced Check all that apply. when the loop is moved sideways across the page. when the size of the loop decreases. when the magnetic field is tilted so it is no longer perpendicular to the page. when the magnetic field gets stronger.

when the size of the loop decreases. when the magnetic field is tilted so it is no longer perpendicular to the page. ?????

A wire loop moves at constant velocity without rotation through a constant magnetic field. The induced current in the loop will be A wire loop moves at constant velocity without rotation through a constant magnetic field. The induced current in the loop will be counterclockwise. zero. clockwise. We need to know the orientation of the loop relative to the magnetic field.

zero. Normally would have change in flux but there is none bc constant filed, no roataion