3 Electromagnetic Induction

Question 1

Describe the shape of the magnetic field around a wire

Answer 1

Circular field shape

field lines getting futher apart- field getting weaker as you move away from the wire

Question 2

How do you determine the direction of a magnetic field around a wire?

Answer 2

Use the right hand grip rule

Thumb- direction of current

Fingers- wrap in direction of magnetic field (clock wise or anti-clockwise)

Question 3

How would you construct a simple electromagnet?

Answer 3

1) wrap a wire around an iron nail
2) connect a cell across the wire

Question 4

What can be done to increase the magnetic field around a solenoid?

Answer 4

1- more turns

2- increase the current

3- add an iron core

Question 5

Draw the shape of a magnetic field around a coil.

Answer 5

Question 6

Draw the magnetic field around a solenoid.

Answer 6

Question 7

What happens to the magnetic field around a wire if more wires are added side by side- How can you tell from the image that the magnetic field is stronger?

Answer 7

More wire- stronger field

The closer the magnetic field lines the stronger the field.

iron filing will line up more easily and more closely together in a stronger magnetic field.

Question 8

If a vertical wire has the current upward in the wire, work out the direction of the magnetic field using your Right Hand Grip Rule

Answer 8

Thumb- up and in direction of current

Finger wrap in direction of magnetic field.

Question 9

How would you demonstrate the direction of the magnetic field around a single wire?

Answer 9

Place compasses around the wire

The compass will point in the direction of the magnetic field

Question 10

What happens to the direction of the magnetic field around a magnet if the direction of the current it reversed?

Answer 10

The direction of the magnetic field is reversed.

Question 11

How do we use dot and crosses to represent the direction of a mangetic field or current?

Answer 11

dot means out of the page

cross means into the page

Question 12

How do you use the right hand grip rule to work out which end of a solenoid is the north end?

Answer 12

Fingers- wrap your fingers in the direction of the current

Thumb- will point to the North end of the solenoid

Question 13

What happens to the magnetic field around a solenoid if you add an iron core (magnetically soft)

Answer 13

Stronger magnetic field

Question 14

Why is iron a better core to use in an electromagnet than steel?

Answer 14

Iron is magnetically soft- the domains in iron line up easily - it can magnetise and demagentise easily

Steel is magnetically hard- the domains do not line up easily- it cannot magnetise easily and it can be used to make permananet magnets becaouse it also does not easily demagnetise

Question 15

Electromagets are used in electric bells.

• When the button is pushed, a current flows in the electromagnet -This creates a magnetic field around the electromagnet
• The electromagnet attracts the soft iron armature which moves to the right
• This causes the hammer to hit the bell.

What happens next?

Answer 15

The moment the iron armature moves to the right this creates a _break in the circuit- t_he circuit is no longer complete.

The current drops to zero and the magnetic field around the electromagnet disappears.

The iron armature is no longer attracted and springs back to the left

The armature completes the circuit again and the whole cycle repeats alowing the bell to repeatedly sound.

Question 16

Answer 16

7. No force at all

Note: Particle is moving parallel to the field- no force.

Question 17

Describe the left hand rule (LHR)

Answer 17

Question 18

Complete the explanation of why the comutator allows the motor to rotate

1. There is a current carrying coil
2. 90º to a magnetic field
3. Using LHR- left side of coil experiences an upward force.
4. Using LHR- current is travelling the opposite direction on the right side of coil- it experiences a downward force
5. Coil rotates clockwise

Answer 18

6. When coil is at 90º, the current in the coil reverses due to the commutator and brushes.
7. Current continues to travel IN on the left and OUT on the right

8 Using LHR- left side of coil still experiences an upward force and the right hand side still experiences a downward force

9. Coil continues to rotate clockwise

Question 19

When the magnet is moved into the coil, a current is induced and the needle on the ammeter moves to the left.

Describe what happens when the magnet is pulled out of the coil.

Answer 19

The needle with move to the right

Reversing the direction of the magnet, reverses the induced current

Question 20

When a magnet is moved in and our of a coil, a current is induced in the coil. What is this phenomenon called?

Answer 20

Electromagnetic induction

Question 21

Explain why a current is induced in the coil when the magnet is pushed into the coil

Answer 21

1. The magnet is moving (thuMb- MOVEMENT)
2. The magnetic field lines of the magnet are cutting the wires of the coil at 90º - (First finger- FIELD)
3. This induces a current in the coil - (seCond finger- CURRENT)

Question 22

Explain why a current is induced in a wire when it it is moved downward through a magnetic field

Answer 22

1. Wire is moved downward (thuMb - MOVEMENT)
2. The wire cuts the magnetic field lines at 90º - First finger- FIELD)
3. This induces a current in the wire- (seCond finger- CURRENT)

Question 23

When a wire is moved down through a magnetic field, the wires cut the magnetic field lines at 90º and this induces a current in the wire which moves the ammeter needle to the left.

What happens when the wire is pulled up and out of the magnetic field?

Answer 23

The needle will move to the right

Reversing the direction of the movement of the wire will reverse the direction of the induced current.

Question 24

When a wire is moved downward through a magnetic field, the wire cuts the magnetic field lines at 90º and induces a current in the wire.

What would happen if the wire is moved more quickly?

Answer 24

A large current would be induced

Question 25

When a wire is moved downward through a magnetic field, the wire cuts the magnetic field lines at 90º and induces a current in the wire.

What would happen if the strength of the magnets were increased?

Answer 25

A large current would be induced

Question 26

When a wire is moved downward through a magnetic field, the wire cuts the magnetic field lines at 90º and induces a current in the wire.

What would happen if the number of turns in the wire was increased?

Answer 26

A large current would be induced

Question 27

When a magnet is moved in and out of a coil, the magnetic field lines of the magnet cut the coil at 90º , which induces an a.c. current.

State three way in which you could increase the current induced?

Answer 27

1. More turns in the coil
2. Stronger magnet
3. Move the magnet faster

Question 28

Use the LHR to explain why a current is induced in the coil

Answer 28

1. Magnet is moved (thuMb- MOVEMENT)
2. Magnetic field lines around magnet cut the coil at 90º (First finger- FIELD)
3. Due to LHR a current is induced in the coil (seCond finger- CURRENT)

Question 29

Use the LHR to explain why a current is induced in the wire.

Answer 29

1. Wire is moved (thuMb- MOVEMENT)
2. 90º to a magnetic field (First finger- FIELD)
3. Due to LHR a current is induced in the wire (seCond finger- CURRENT)

Question 30

Use the LHR to explain why a current is induced in the wire.

Answer 30

1. Wire is moved (thuMb- MOVEMENT)
2. 90º to a magnetic field (First finger- FIELD)
3. Due to LHR a current is induced in the wire (seCond finger- CURRENT)

Question 31

Use the LHR to explain why the wire moves to the left.

Answer 31

1. Current carrying wire (seCond finger- CURRENT)
2. 90º to magnetic field (First finger field)
3. Using LHR this creates a force to the left- wire moves left (thuMb movement)