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Flashcards in Magnetism Deck (13)
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1

What is a solenoid? How can it made stronger?

A coil of current carrying wire. The magnetic field inside a solenoid is strong and uniform. It can be made stronger by putting a soft iron core in the middle.

2

What is special about a current carrying wire?

It has a magnetic field

3

What is the motor effect?

A current carrying wire that is in a magnetic field experiences a force. This is because the magnetic field of the wire and another magnetic field interact with eachother.

4

When does the wire experince the full force? (In the motor effect)

When it is at 90 degrees to the opposing magnetic field

5

What are the four factors that speed up a simple D.C motor?

- More current
- More turns on the coil
- Stronger magnetic field
- A soft iron core in the coil

6

Describe how loudspeakers work.

- They work because of the motor effect.
- A.C electrical signals from an amplifier are fed to a coil of wire in the speaker which is wrapped around the base of a cone.
- The coil is surrounded by a permanent magnet, so the a.c. signals cause a force on the wire, causing it to move back and forth
- These movements make the cone vibrate and this creates sound

7

What is electromagnetic induction?

The creation of a voltage in a wire which is experiencing a change in magnetic field.

8

What is the dynamo effect?

Using the concept of electromagnetic induction to transform kinetic energy into electrical energy is called the dynamo effect. Practically, this means moving a current-carrying wire or the magnet around it so that it experiences a change in magnetic field and a voltage can be induced.

9

To get a bigger voltage in electromagnetic induction you can increase...

- The strength of the magnet used
- The number of turns on the coil
- The speed of movement

10

Describe how an A.C generator works.

- Generators rotate a coil in a magnetic field
- As the coil spins, a current is induced in the coil. This current changes direction every half turn
- Generatorsd don't have split ring commutators so the contacts don't swap every half turn.
- This means they produce an a.c. voltage

11

How are a.c. generators different from d.c motors?

In a motor: a current in a wire in a magnetic field, which causes movement.
In a generator: a magnetic field and movement, which induces a current.

12

What is the function of a transformer?

They change the size of the voltage of an alternating current. This is so power can be transmitted efficiently.

13

How do transformers work?

- They have two coils of wire (primary and secondary), joined with an iron core
- When an alternating voltage is applied across the primary coil the magnetically soft iron magnetises and demagnetises quickly.
- This induces an alternating voltage in the secondary coil.
- The number of turns or each coil determines wether the voltage is magnified or reduced.