Electromagnet Physic Test( Anderson)

A horizontal straight wire carries a current from east to west. The resulting magnetic field lines are

closed circles perpendicular to the wire directed clockwise as viewed from the east.

The current reversals required for continuous rotation of the armature in a dc motor are accomplished by using a(n)

commutator

Imagine that this classroom contains a constant magnetic field that points from the front to the back. In front of you a negative charge is slowly moving horizontally to your left. As you watch, the magnetic force on the charge

deflects the charge into a counterclockwise vertical circle.

The current with which a transformer is used

must be ac.

equation for radius of deflection

r=mv/qB

The magnetic forces exerted on each other by two parallel wires with unequal currents flowing in opposite directions is

repulsive and equal in magnitude.

Two long wires are parallel to each other. The wires carry currents of different magnitudes. If the amount of current in each wire is halved, the magnitude of the force between the wires will be

one fourth the original force.

A solenoid carrying an electric current, if free to rotate when placed in a magnetic field, will tend to orient its axis ____________________ (parallel, perpendicular, anti-parallel) to the magnetic field.

parallel

Are the magntic field lines always perpendicular or parallel the current?

perpendicular

The torque on a solenoid is a maximum when the solenoid axis is ____________________ to the magnetic field.

perpendicular

A current-carrying loop in a magnetic field always tends to turn until the plane of the loop is

perpendicular to the field.

The north pole of a bar magnet is moved away from a single closed loop of wire along the axis of the loop. The induced current in the loop produces an effective ____________________ pole toward the bar magnet.

south

Direct electric current cannot be used to operate

transformers.

A positively charged ping pong ball is sitting stationary on the floor in the center of a room. There is also a constant, uniform magnetic field in the room that points toward the ceiling. If I now start the ball rolling toward the back of the room, the resultant motion of the ball, as observed from the ceiling, will be

a horizontal, clockwise circle.

A magnet does not exert a force on

a stationary electric charge

Which of the following cannot induce a voltage in a loop of wire?

Expanding or contracting the loop in a region where there is no magnetic field.

force equation for parallel wire

F/L= 2K(I1)(I2)/r

When there is a changing magnetic flux through an electric circuit, the direction of the induced current in the circuit is determined by ____________________ Law.

Lenz

Equation for transformers

N1/N2= V1/V2

Faraday's Law states that a voltage is induced in a circuit when there is a changing ____________________ passing through the circuit.

South

A battery is causing a large current in a solenoid (helical coil of wire). A bar magnet is held at rest nearby, aligned with the axis of the solenoid, with its south pole closest to the solenoid. The bar magnet is being repelled by the solenoid. Which of the following statements is true of the conventional current in the solenoid?

The direction of the current in the solenoid alternates with a constant frequency

A current-carrying wire is in a magnetic field with the direction of the current parallel to that of the field.

The wire has no tendency to move or to turn.

A loop of wire lies motionless on a flat, horizontal surface in the presence of a uniform and constant magnetic field. When is the magnetic flux through the area interior to the loop the largest?

. when the magnetic field is perpendicular to the area interior to the loop

The south pole of a bar magnet is moved toward a short helical coil of wire (solenoid) along the axis of the coil. The coil has 100 turns and the ends of the coil are connected to form a closed circuit. If the coil is replaced with a single loop of the same type of wire, and the magnet is moved exactly as before, the current induced in the loop is

100 times smaller.

What does K equal?

1E-7 N/a2

A bar magnet is held near a single closed loop of wire. The magnet is facing the loop on its normal, and the north pole is facing the loop. If the magnet is moved away, the current induced in the loop will be in a ____________________ direction as viewed from the side the magnet is on.

Clockwise

The primary coil of a transformer is connected to a source of alternating current of voltage V. The voltage of the secondary current is A. lower than V. B. equal to V. C. higher than V. D. Any of these choices could be correct, depending on the ratio of turns in the transformer coils.

D. Any of these choices could be correct, depending on the ratio of turns in the transformer coils.

Imagine a magnetic field pointing into the plane of this page. An electron moves across the paper from left to right. The direction of the magnetic force on the electron will be

in the plane of the paper and toward the bottom of the page

14. In diagrams of magnetic fields, the symbol "x" is used to represent

the magnetic field going into the paper.