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Flashcards in Magnetism Deck (13)
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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.


What is special about a current carrying wire?

It has a magnetic field


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.


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

When it is at 90 degrees to the opposing magnetic field


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


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


What is electromagnetic induction?

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


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.


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


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


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.


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.


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.