Electromagnetism

Question 0

How can the magnetic field change?

Answer 0

• if the conductor is moving into or out of a magnetic field
• if a magnet is moving towards or away from a conductor
• if the magnetic field is being varied

Question 1

Electromagnetic induction

Answer 1

When a conductor is in a changing magnetic field a voltage is induced in the conductor.

If we move a wire across a magnetic field at right angles a voltage is induced in the wire. If wire is part of complete circuit then a current flows.

Question 2

Size of induced voltage can change with:

Answer 2

• the wire moving more quickly.
• using a stronger magnet.
• wrapping the wire into a coil so that more pieces of wire move through the magnetic field. (More turns)
• using a coil with a greater area

Question 3

Size of induced voltage

Answer 3

Depends on rate at which the magnetic lines of flux (field lines) are cut.

Question 4

Faradays law of electromagnetic induction

Answer 4

The size of the induced voltage is directly proportional to the rate at which the magnetic lines of flux are being cut.

Question 5

Two types of generators

Answer 5

1. Bycicle dynamo

2. Larger generator

Question 6

Step down transformer

Answer 6

N1 > N2

Question 7

Step up transformer

Answer 7

N2 > N1

Question 8

Strength of magnetic field around a current-carrying wire can be increased by: (2)

Answer 8

1. Increasing the current in the wire.

2. Wrapping the wire into a coil or solenoid (long coil)

Question 9

Strength of field around solenoid can be increased by: (3)

Answer 9

1. Increasing current flowing through the solenoid
2. Increasing number of turns
3. Wrapping solenoid around magnetically soft core such as iron.

Question 10

Describe the construction of an electromagnet.

Answer 10

An electromagnet is constructed by wrapping a current-carrying coil or solenoid around a soft iron (magnetic) core.

Question 11

Force on a current-carrying conductor in a magnetic field increases with:

Answer 11

• 1. Strength of field

* 2. Size of current

Question 12

To increase rate at which the motor turns we can:

Answer 12

1. Increase number of turns or loops of wire (to make a coil)
2. Increase strength of magnetic field.
3. Increase current.

Question 13

How does a practical motor differ from a simple electric motor?

Answer 13

• 1. Permanent magnets are replaced with curved electromagnets that are capable of producing very strong magnetic fields.
• 2. The single loop is replaced with several coils of wire wrapped on the same axis making the motor more powerful and allowing it to run more smoothly.
• 3. Coils are wrapped on a laminated soft iron core to make motor more efficient and powerful.

Question 14

Size of induced voltage and current can be increased by:

Answer 14

1. Moving the wire more quickly
2. Using stronger magnet
3. Wrapping the wire into a coil so more of the wife cuts through magnetic field.

Question 15

Size of induced voltage by pushing magnet into coil can be increased by:

Answer 15

1. Moving the magnet more quickly
2. Using a stronger magnet
3. Using a coil with more turns
4. Using a coil with a larger cross sectional area.

Question 16

How does the rate at which the magnetic field lines are cut affect the size of the induced voltage?

Answer 16

The faster the lines are cut the larger the induced voltage and current

Question 17

What happens when a conductor is in a changing magnetic field?

Answer 17

A voyage will be induced in the conductor?

Question 18

How can a magnetic field change?

Answer 18

1. If conductor is moving in or out of the magnetic field.
2. If a magnet is moving towards or away from the conductor.
3. Magnetic field is being varied

Question 19

How does a transformer work?

Answer 19

Alternating current is passed through the coil and so the magnetic field is continually changing.
- if a second coil is placed near the first the changing magnetic field passes through it and as it cuts through the wires of the second coil a voltage is induced on that coil.
• size and direction of the induced voltage changes as the voltage applied to the first coil changes.