Magnetism

Question 1

What is a solenoid? How can it made stronger?

Answer 1

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.

Question 2

What is special about a current carrying wire?

Answer 2

It has a magnetic field

Question 3

What is the motor effect?

Answer 3

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.

Question 4

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

Answer 4

When it is at 90 degrees to the opposing magnetic field

Question 5

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

Answer 5

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

Question 6

Describe how loudspeakers work.

Answer 6

• 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

Question 7

What is electromagnetic induction?

Answer 7

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

Question 8

What is the dynamo effect?

Answer 8

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.

Question 9

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

Answer 9

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

Question 10

Describe how an A.C generator works.

Answer 10

• 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

Question 11

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

Answer 11

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.

Question 12

What is the function of a transformer?

Answer 12

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

Question 13

How do transformers work?

Answer 13

• 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.