# 3 Electromagnetic Induction Flashcards

1
Q

Describe the shape of the magnetic field around a wire

A

Circular field shape

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

2
Q

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

A

Use the right hand grip rule

Thumb- direction of current

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

3
Q

How would you construct a simple electromagnet?

A

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

4
Q

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

A

1- more turns

2- increase the current

5
Q

Draw the shape of a magnetic field around a coil.

A
6
Q

Draw the magnetic field around a solenoid.

A
7
Q

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?

A

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.

8
Q

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

A

Thumb- up and in direction of current

Finger wrap in direction of magnetic field.

9
Q

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

A

Place compasses around the wire

The compass will point in the direction of the magnetic field

10
Q

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

A

The direction of the magnetic field is reversed.

11
Q

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

A

dot means out of the page

cross means into the page

12
Q

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

A

Fingers- wrap your fingers in the direction of the current

Thumb- will point to the North end of the solenoid

13
Q

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

A

Stronger magnetic field

14
Q

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

A

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

15
Q

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?

A

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.

16
Q
A
1. No force at all

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

17
Q

Describe the left hand rule (LHR)

A
18
Q

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
A
1. When coil is at 90º, the current in the coil reverses due to the commutator and brushes.
2. 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

1. Coil continues to rotate clockwise
19
Q

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.

A

The needle with move to the right

Reversing the direction of the magnet, reverses the induced current

20
Q

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

A

Electromagnetic induction

21
Q

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

A
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)
22
Q

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

A
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)
23
Q

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?

A

The needle will move to the right

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

24
Q

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?

A

A large current would be induced

25
Q

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?

A

A large current would be induced

26
Q

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?

A

A large current would be induced

27
Q

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?

A
1. More turns in the coil
2. Stronger magnet
3. Move the magnet faster
28
Q

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

A
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)
29
Q

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

A
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)
30
Q

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

A
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)
31
Q

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

A
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)
32
Q
A
33
Q
A