Conceptual problems Chpt 29
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
The negative sign in the Faraday's equation for electromagnetic induction is related to the direction of the induced emf. True False
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 False
True
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
In a transformer, the power input: -is equal to the power output. -is smaller than the power output. -is larger than the power output. -can be either larger or smaller than the power output.
Is equal to the power output
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? -produce the greatest voltage -produce a greater heating effect -enhance the effect which produces it -produce the smallest voltage -oppose the effect which produces it
Oppose the effect which produces it
If the number of turns on the secondary coil of a transformer are less than those on the primary, the result is a -step-up transformer. -a dc transformer. -step-down transformer. -120-V transformer. -220-V transformer.
Step-down transformer
Magnetic flux depends upon -the magnetic field. -the orientation of the area with respect to the field. -the area involved. -all of the above -none of the above
All of the above
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
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. If the magnet is dropped from this position what is the direction of the induced current in the coil? -There is no current in the coil. -counterclockwise -clockwise -Not enough information is provided.
Counterclockwise
Electric power is transmitted over long distances at high voltage because : -the lines can be on taller poles. -electricity moves faster at higher voltage. -lightning does more damage. -there is less power lost. -electricity moves slower at higher voltage.
There is less power lost
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. -clockwise -counterclockwise -Not enough information is provided.
There is no current in the coil
A transformer is a device used to -transform an alternating current into a direct current. -transform a direct current into an alternating current. -increase or decrease an ac voltage. -increase or decrease a dc voltage.
increase or decrease an ac voltage
