A2 Topic 7 Electromagnetic Induction

What is the cause of an induced current?

• A series of cells with a high EMF.

• Strong magnet close to a conductor.

• Long wire in a magnetic field.

• Relative motion between a coil and a magnetic field.

What is the direction of the current in this magnetic field?

• Clockwise

• Anti-clockwise

• Towards the observer

• Away from the observer

Which description best applies to Lenz's Law?

• An induced current occurs when a magnet passes through a tube.

• When a change in magnetic field occurs to a coil the direction of induced current goes in a direction to oppose this change.

• The direction of an induced current is such to align with the change that created it.

• A magnet is a tube is always slowed by its magnetic field.

What is the unit for flux?

• Weber (Wb)

• Weber-coils (Wb-coils)

• Tesla-lines (T-lines)

• Tesla-coils (T-coils)

Which is NOT an equation for induced EMF?

• E=-Bvl

• E=-NΔΦ÷Δt

• E=-NΔ(BAcosθ)/Δt

• E=-(Bvl)/N

A loop of wire with area 0.32 m² site is a magnetic field with strength 0.89 T. Calculate the magnetic flux through the loop when perpendicular?

• 0.285 Wb

• 0.28 T

• 0.42 Wb

• 0.40 T

What happens when a low voltage d.c. supply connected to a coil is switched off?

• A large back emf is induced to oppose the rapid loss of the magnetic field of the coil

• A small back emf is induced to oppose the rapid loss of the current

• A large back emf is induced to oppose the rapid loss of the magnetic field of the supply

• A back emf is induced to oppose the rapid loss of current in the circuit

Faraday's law in words

• The emf induced in a conductor is proportional to the rate of change of magnetic flux linkage

• The current induced in a conductor is proportional to the rate of change of magnetic flux

• The emf induced in a conductor is proportional to the rate of change of magnetic flux

• The emf induced in a conductor is proportional to the rate of change of magnetic field strength

A coil with 120 turns with area 0.070 m² is placed in a magnetic field whose flux density changes from 80 mT to 20 mT in 4.0 s. What emf is induced in the coil in this time?

• 130 mV

• 170 mV

• 500 mV

• 110 mV

When a small magnet is dropped down a long aluminium tube it takes longer than expected since

• the magnet is attracted to the sides of the tube

• the relative velocity causes a change of flux across the tube which induces an opposing emf, eddy current and magnetic field

• the magnet nearly fills the area of the tube causing air pressure to build up and oppose the movement

• eddy currents are induced in the magnet which oppose the movement