Electromagnetism And Electric Motors

Question 1

How may a long straight wire or coil have a magnetic field?

Answer 1

If an electric current is flowing through it.

Question 2

If we have a wire, how can we make a much larger magnetic field?

Answer 2

Wrap the wire in the form of a long straight coil.

Question 3

What is a solenoid?

Answer 3

A wire wrapped in the form of a long, straight coil.

Question 4

How can we increase the magnetic field strength of a coil of wire carrying an electric current?

Answer 4

1. Use a larger current
2. Use more turns of wire
3. Put a soft iron rod into the solenoid.

Question 5

How can we deduce the direction of the magnetic field of a solenoid?

Answer 5

Look end-on at the solenoid.
If the current flows clockwise, that end is south.
If the current flows anticlockwise, that end is north.

Question 6

What is the motor effect?

Answer 6

Where a current-carrying wire placed inside a magnetic field experiences a force.

Question 7

Where is the direction of the force that a current-carrying wire in a magnetic field experiences?

Answer 7

Perpendicular to the field lines and current

Question 8

What happens if we reverse the direction of the current or magnetic field with a current-carrying wire?

Answer 8

The direction of the force will reverse.

Question 9

When is the size of the force on a current-carrying wire greatest in a magnetic field?

Answer 9

When the current is perpendicular to the field lines.

Question 10

When is the size of the force on a current-carrying wire zero in a magnetic field?

Answer 10

When the current is parallel to the magnetic field lines.

Question 11

In what is the motor effect used?

Answer 11

An electric motor.

Question 12

From what does the force of a current-carrying wire in a magnetic field arise?

Answer 12

The interaction of the magnetic field of the current with the magnetic field of the permanent magnet.

Question 13

What kind of magnetic field does a current-carrying wire have?

Answer 13

A circular magnetic field.

Question 14

What kind of magnetic field does a north and south pole have when facing each other across a gap?

Answer 14

A linear magnetic field.

Question 15

How do we work out the direction of the force on the current-carrying wire in a magnetic field?

Answer 15

We use Fleming’s Left Hand Rule

Question 16

How do we use Fleming’s Left Hand Rule?

Answer 16

Point the first finger in the direction of the field.
Point the second finger in the direction of the current.
Then, the thumb points in the direction of the force or motion.

Question 17

What direction is a magnetic field always?

Answer 17

From north to south.

Question 18

What direction does the current flow in a wire?

Answer 18

From the positive terminal of a battery to the negative terminal.

Question 19

When is the force on the coil greatest in a magnetic field?

Answer 19

When the coil is horizontal.

Question 20

How does an electric motor work?

Answer 20

When the coil is horizontal, the forces on the sides are vertical, opposite in direction and at their maximum.
When the coil becomes vertical, the commutator reverses direction of the current so that it keeps rotating the same direction.

Question 21

In an electric motor, what does a user supply and to produce what?

Answer 21

A user supplies an electric current a magnetic field to produce motion.

Question 22

Why is the wire used in the coil surrounding the electromagnet insulated?

Answer 22

So that no current flows in the core.