Electromagnetism Flashcards

Flashcards for reviewing electromagnetism concepts, formulae, experiments, and applications.

What are the metals that show magnetic properties?

Iron, nickel, cobalt, and some of their alloys.

What causes a magnetic field?

A moving electric charge.

What is a magnetic field line?

A line that indicates the direction a ‘magnetic north’ would travel in a magnetic field if free to do so.

What is believed to cause earth magnetic field?

Convection currents of molten iron in the Earth’s core.

How can the direction of the field around a current carrying conductor be found?

By the ‘right hand grip rule’ or 'Maxwell’s corkscrew'.

What happens when an electric current is passed through the wire of an electromagnet?

A magnetic field is set up.

What is magnetic flux density (B)?

A measure of the strength of the magnetic field. It is a vector quantity with an SI unit of tesla (T).

What is the formula for the force on a current-carrying conductor in a magnetic field?

F = IlBsinθ, where θ is the angle between the direction of the current and the magnetic field.

What does Fleming's Left Hand rule indicates?

The direction of the force (F), magnetic flux density (B), and current (I).

What happens if a charged particle enters a magnetic field at constant speed travelling perpendicularly to the field?

The particle moves in a circle.

What is the formula for the force on a charged particle moving through a magnetic field?

F = qvB

What is the relationship between two parallel wires when the current flows in the same direction?

The force is attractive.

Define Ampere.

The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible cross section and placed 1 metre apart in a vacuum, would produce a force on each conductor of 2  10-7 newtons per metre of length.

What is electromagnetic induction?

Where an emf is induced by a change in the magnetic flux linking a circuit.

What is magnetic flux (Φ)?

The total amount of magnetic field in a given region; it is the product of magnetic flux density (B) and area (A). Its SI unit is weber (Wb).

State Faraday’s law.

The magnitude of the induced emf is proportional to the rate of change of flux linking a circuit.

State Lenz’s law.

The direction of the induced emf is always such as to oppose the change causing it.

What are eddy currents?

Circulating electrical currents (like little whirlpools) that are induced in electrically conductive materials when exposed to changing magnetic fields, creating an opposing force to the magnetic flux.

What energy conversion happen as a disc slows down due to electromagnetic damping?

Kinetic to electrical to heat.

What is the formula for induced emf in a solenoid?

E = -N (dΦ/dt)

What is an alternating current (a.c.)?

An electric current whose direction reverses periodically.

What is a direct current (d.c.)?

An electric current that flows continuously in the same direction.

Why is mains electricity a.c.?

Because it is easier to generate and it is more efficient to transport.

What is the relationship between peak voltage (V0) and r.m.s. voltage (Vrms)?

Vrms = V0 / √2

What is the relationship between peak current (I0) and r.m.s. current (Irms)?

Irms = I0 / √2

What is mutual induction?

Where a changing magnetic field in one coil induces an emf in another coil.

What is a transformer?

An electrical device used to change the voltage of a.c. power supplies. It operates on the principle of mutual induction.

What is the transformer formula?

Vi/Vo = Np/Ns

What are factors affecting the efficiency of transformers?

Eddy currents (in the iron core) / heat or energy losses in the (low voltage) coil / shape of core / core laminations.

What is self-induction?

Where a changing magnetic field in a coil induces an emf in the coil itself.

What is an inductor?

An electrical device used to induce a back emf.