Physics final conceptual

The force on a current-carrying wire in a magnetic field is equal to zero when

the current is parallel to the field lines.

Cutting a bar magnet near its north end results in a smaller mostly north pole magnet and a larger mostly south pole magnet.

False

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

False

For the maximum induced emf in the coil of a generator, the term sin ωt has a value of zero.

False

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

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

False

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

False

There is an induced emf in a wire that is moving parallel to a magnetic field if the wire is moving in the opposite direction to that of the magnetic field.

False

In a velocity selector having electric field E and magnetic field B, the velocity selected for positively charged particles is v = E/B. The formula is the same for a negatively charged particles.

True

Magnetic field lines can never cross one another.

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

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

True

The magnetic field unlike the electric field is continuous.

True

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

True

There is no induced emf in a wire that is moving parallel to a magnetic field if the wire is moving in the direction of the magnetic field.

True

Magnetic flux depends upon

*The magnetic field *The area involved. *The orientation of the area with respect to the field.

What fundamental fact underlies the operation of essentially all electric motors?

A current-carrying conductor placed perpendicular to a magnetic field will experience a force.

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

False

A wire of length L carrying a current I is placed in a magnetic field. The direction of the magnetic field is opposite the direction of the current. In this situation, the wire experiences a maximum force.

False

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

False

A vertical wire carries a current straight down. To the east of this wire, the magnetic field points

South

A coil is rotating at constant speed within a uniform magnetic field. What can be said about the magnitude of the emf induced in the coil?

The magnitude of the induced emf reaches its maximum value whenever the plane of the coil is perpendicular to the direction of the field.

A rectangular coil lies flat on a horizontal surface. A bar magnet is held above the center of the coil with its north pole pointing down. What is the direction of the induced current in the coil?

There is no current in the coil.

A changing magnetic field can produce an electric current.

True

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

True

A charged particle traveling opposite to a magnetic field does not experience a magnetic force.

True

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

True

A current carrying wire placed in a magnetic field perpendicular to the wire experiences a maximum force.

True

A rectangular coil carrying a current in a magnetic field will experience a net torque that will cause the coil to rotate in that field, if the field is not along the coil axis.

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

An emf is induced in a wire by changing the current in a nearby wire.

True

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

True

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

True

At a given location the direction of the magnetic field is the direction that the north pole of a compass points when placed at that location.

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

As a coil is removed from a magnetic field an emf is induced in the coil causing a current to flow within the coil. This current interacts with the magnetic field producing a force whic

acts in the direction opposite to the coil's motion.

A piece of soft iron is placed in a solenoid increasing the magnetic field in an arrangement that can be switched on and off. Such a device is called

an electromagnet

In using Ampere's law, the integral must be evaluated

around a closed path.

A horizontal wire carries a current straight toward you. From your point of view, the magnetic field caused by this current

circles the wire in a counter-clockwise direction

A circular loop of wire of area 25 cm2 lies in the plane of the paper. An increasing magnetic field B is coming out of the paper. What is the direction of the induced current in the loop?

clockwise

A circular coil of copper wire is lying flat on a horizontal table. A bar magnet is held with its south pole downward, vertically above the center of the coil. The magnet is released from rest and falls toward the coil. As viewed from above, you can say that, as it falls, the magnet induces

clockwise current in the loop.

A long, straight wire carrying a current is placed along the y-axis. If the direction of the current is in the +y direction, what is the direction of the magnetic field due to this wire?

counterclockwise, around the y-axis

A charged particle is injected into a uniform magnetic field such that its velocity vector is perpendicular to the magnetic field vector. Ignoring the particle's weight, the particle will

follow a circular path.

A transformer is a device used to

increase or decrease an ac voltage.

A square loop of wire carrying a current in a clockwise direction lies in the plane of the paper. The magnetic field inside the loop is directed

into the paper everywhere.

In a transformer, the power input

is equal to the power output

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

is zero

A vertical wire carries a current straight up in a region where the magnetic field vector points due north. What is the direction of the resulting force on this current?

west

An electric current produces

magnetic field

An electric generator transforms

mechanical energy into electrical energy

The magnetic permeability of a ferromagnetic material is

much greater than μo.

According to Lenz's law, the direction of an induced current in a conductor will be that which tends to produce which of the following effects?

oppose the effect which produces it

The direction of the force on a current-carrying wire in a magnetic field is described by which of the following?

perpendicular to both the current and the magnetic field

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 down

A current carrying loop of wire lies flat on a table top. When viewed from above, the current moves around the loop in a counterclockwise sense. What is the direction of the magnetic field caused by this current, outside the loop? The magnetic field

points straight down

A current carrying circular loop of wire lies flat on a table top. When viewed from above, the current moves around the loop in a counterclockwise sense. What is the direction of the magnetic field caused by this current, inside the loop? The magnetic field

points straight up

The magnetic field produced by a long straight current-carrying wire is

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

If the number of turns on the secondary coil of a transformer are less than those on the primary, the result is a

step down transformer

Two long parallel wires are placed side-by-side on a horizontal table. If the wires carry current in opposite directions,

the wires repel each other

Electric power is transmitted over long distances at high voltage because

there is less power lost

A proton, moving west, enters a magnetic field of a certain strength. Because of this magnetic field the proton curves upward. What is the direction of this magnetic field?

towards the south

An electron, moving south, enters a magnetic field of certain strength. Because of this field the electron curves upward. What is the direction of the magnetic field?

towards the west

The ampere is defined

using the force between current carrying wires