3.13 Electromagnetism

Question 1

As a current flows through a wire, a magnetic field is created around the wire. What is the magnetic field made of?

Answer 1

Concentric circles perpendicular to the wire, with the wire in the gender

Question 2

How would magnetic fields around a circular coil work?

Answer 2

The magnetic fields would stretch out and form ellipses as they interact with each other. Also, as the magnetic fields combine they form a single magnetic field which runs straight through the centre of the coil.

Question 3

How can you increase the strength of the magnetic field that a current-carrying wire produces?

Answer 3

By wrapping the wire into a coil called a solenoid

Question 4

Describe a solenoid

Answer 4

• You can increase the strength of the magnetic field that a current-carrying wire produces by wrapping the wire into a coil called a solenoid.
• The magnetic field strength increases because the fields around each turn of wire line up with each other.
• The magnetic field inside a solenoid is strong and uniform (it has the same strength and direction at every point in that region).
• Outside the coil, the magnetic field is just like the one round a bar magnet

Question 5

How can the magnetic effect of a solenoid be increased? (4)

Answer 5

By:
- Increasing the current through the coil
- Increasing the number of turns but keeping the length the same
- Decreasing the cross-sectional area of the solenoid
- Adding a block of iron in the centre of the coil. This iron core becomes an induced magnet whenever current is flowing, so the magnetic effect of the solenoid is increased.

Question 6

What is a current-carrying solenoid with an iron core called?

Answer 6

An electromagnet - a magnet with a magnetic field that can be turned on and off by turning the current on and off

Question 7

When electromagnets were discovered in the 19th century, it led to the creation of lots of devices. What is one example of these?

Answer 7

Electromagnetic relays

Question 8

What did the electromagnetic relay invention lead to?

Answer 8

Huge advances in communications as they allowed coded messages to be sent long distances as electrical signals before being translated back into words (telegraphs).

Question 9

How do electromagnetic relays work? (2)

Answer 9

• When the switch in circuit one is closed, it turns on the electromagnet, which attracts the iron contact on the rocker.
• The rocker pivots and pushes together the contacts, completing circuit two and generating an electrical signal.