Electromagnetism & The Motor Effect Practice Questions

Which of these describes the shape of the magnetic field produced by the current in the wire?

Put a cross ( ☒ ) in the box next to your answer.

☐ A straight lines parallel to the wire

☐ B circles centred on the wire

☐ C straight lines pointing away from the wire

☐ D straight lines pointing towards the wire

A plotting compass is placed on the bench a short distance from the wire.

State two changes that would increase the strength of the magnetic field at the position of the compass.

Calculate the size of the force on the wire.

Use the equation

$F = B \times I \times l$

force on the wire = ............................................... N

The connections to the battery are then swapped over, so that the current in the wire is reversed.

State the effect of this on the force on the wire.

Describe how to use Fleming's left-hand rule to find the direction of the force on the wire.

Give one change the student could make to the apparatus so that the force on the wire acts in the opposite direction.

Explain why the magnetic field inside the solenoid is strong and almost uniform, while the field outside the solenoid is much weaker.

Give two changes that would increase the strength of the magnetic field produced by the solenoid.

Describe how the student could use a plotting compass to show that the current produces a magnetic field around the wire.

Draw, on the diagram of the card, the magnetic field produced by the current in the wire.

Explain why the reading on the balance increases.

The current in the wire is then reversed, with the same size of current.

State what happens to the reading on the balance.

What is the direction of the current in the wire?

Put a cross ( ☒ ) in the box next to your answer.

☐ A towards the north pole of the magnet

☐ B towards the south pole of the magnet

☐ C into the page

☐ D out of the page

Explain, in terms of magnetic fields, why there is a force on the wire.

Explain how the current in the coil produces a strong magnetic field, and describe how the design of the electromagnet could be changed so that it can lift heavier pieces of steel.

Calculate the magnetic flux density of the field.

Use an equation selected from the list of equations at the end of this paper.

magnetic flux density = ............................................... T

The test is repeated in the same magnetic field. This time the current is doubled and the length of wire inside the field is halved.

State and explain the effect of these changes on the size of the force on the wire.

A horizontal straight wire of length $6.0\,\mathrm{cm}$ lies at right angles to a uniform magnetic field of flux density $0.25\,\mathrm{T}$.

The current in the wire is adjusted until the upward force on the wire is just large enough to support a mass of $1.5\,\mathrm{g}$ hanging from it. The weight of the wire itself can be ignored.

(gravitational field strength $g = 10\,\mathrm{N/kg}$)

Calculate the size of the current in the wire. Use an equation selected from the list of equations at the end of this paper.

current = ............................................... A