Electromagnetism

Question 1

Are magnetic forces contact or non-contact?

Answer 1

Non-contact

Question 2

What is a magnet?

Answer 2

An object capable of exerting a magnetic force.

Question 3

What is the difference between a permanent and an induced magnet?

Answer 3

Permanent is always magnetic whilst induced only becomes a magnet when it’s in a magnetic field. Induced can only attract.

Question 4

Describe magnetic field lines?

Answer 4

They point from the North Pole to the South Pole and don’t cross each other. It is strongest where they are closest.

Question 5

What is the Earth’s magnetic field caused by?

Answer 5

The iron and nickel core.

Question 6

What is a magnetic field?

Answer 6

Area surrounding a magnet that can exert a force on magnetic materials.

Question 7

What is a solenoid?

Answer 7

A coil of wire carrying an electrical current - its shape causes a stronger magnetic field.

Question 8

What does an electromagnet consist of? What is an example of where they are used?

Answer 8

A solenoid with an iron core.
An electric door bell.

Question 9

What is Flemings left hand rule used for?

Answer 9

To find the direction of a force on a conductor in a magnetic field.

Question 10

Fleming’s left hand rule:
Thumb
Forefinger
Second finger

Answer 10

Thumb - movement
Forefinger - field
Second finger - current

Question 11

What is a dc motor?

Answer 11

An electrical device that uses direct current to produce a turning effect.

Question 12

What is a split ring commutator’s purpose?

Answer 12

To keep the motor rotating in the same direction by allowing the current in the coil to change direction each half-turn as the coil rotates.

Question 13

What will increase the strength of the magnetic field around a wire carrying a current?

Answer 13

Increasing the current.

Question 14

What is the effect of putting an iron core inside a solenoid?

Answer 14

The electromagnet becomes stronger.

Question 15

What are poles?

Answer 15

Ends of a magnet where the magnetic forces are strongest.

Question 16

Describe how a material becomes a magnet?

Answer 16

When a magnetic material is placed in a magnetic field, a magnetic field is induced and the material becomes a temporary magnet. When the material is removed from the magnetic fields the induced magnet loses all its magnetism.

Question 17

List some magnetic materials.

Answer 17

Iron
Cobalt
Nickel
Steel

Question 18

How can it be shown that a magnetic material is a permanent magnet?

Answer 18

It will attract and repel another magnet.

Question 19

What do the strengths and directions of magnetic fields depend on?

Answer 19

Strength - distance from the magnet
Direction - the direction of the force that would act on another north pole places at that point

Question 20

Describe how to plot the field line pattern of a bar magnet.

Answer 20

1. Place the compass near the n pole of the magnet
   2.. Mark a small cross where the compass needle is pointing
2. Move the compass so the South Pole of the needle touches this cross
3. Repeat this until the South Pole if the magnet is reached
4. Join the crosses to show the field lines
5. Repeat for different positions from the n pole of the magnet

Question 21

Electromagnetism

Answer 21

The effect where a magnetic field is produced by result of an electric current flowing through a wire.

Question 22

Current flows from … to …

Answer 22

Positive to negative

Question 23

Magnetic field is directly proportional to …
It is inversely proportional to …

Answer 23

Current in the wire
Distance from the wire

Question 24

Describe the right hand grip rule for a wire.

Answer 24

Thumb points in the direction of the current
Fingers point in the direction of the field

Question 25

Describe the magnetic field inside and around a solenoid.

Answer 25

Inside - strong and uniform Around - similar shape to a bar magnet’s magnetic field

Question 26

How can the strength of the magnetic field of a solenoid be increased?

Answer 26

Increasing the current Increasing the number of turns of wire in the coil Add an iron core inside the coil

Question 27

Describe the right hand grip rule for a solenoid.

Answer 27

Fingers curl in the direction of the current Thumb points in the direction of the North Pole.

Question 28

What are the advantages of using an electromagnet instead of a permanent magnet?

Answer 28

They can be switched on and off which is useful for moving magnetic items Their strength can be altered by varying the current

Question 29

How can the magnetic effect of a current be demonstrated?

Answer 29

Iron fillings can be placed near a current carrying wire. The effect on the pattern made by them gives evidence for a magnetic field.

Question 30

What willl happen when a wire carrying a current is placed south to north ina magnetic field?

Answer 30

Nothing because the current is parallel to the magnetic field and so they will not interact as they are not at right angles to each other.

Question 31

What is magnetic flux density?

Answer 31

A measure of the strength of the magnetic field. Tesla.

Question 32

Describe how an electric motor works.

Answer 32

- when the current flows, the force acts upwards on the left side and downwards on the right side of the loop - this produces a clockwise movement as the left side moves up and the right moves down - when the loop is vertical, the force on the loop is zero and there is no movement - the loop has momentum and keeps moving. The split ring commutator swaps the connections with the battery so the current starts flowing again, but in the opposite direction

Question 33

Explain how a force on a wire causes a coil to rotate.

Answer 33

The current travels in opposite directions on each side of the coil of wire so the force acting in each side will be in opposite directions producing a moment on the coil.