Electromagnetism Explanations

Reorder the following statements which explain the function of a loudspeaker

• When an AC current flows through a coil, the coil becomes an electromagnet. The direction of the magnetic field changes.

• The alternating magnetic field around the coil interacts with the magnetic field of the permanent magnetic.

• This means that the coil is constantly getting attracted and repelled by the magnet. 

• This causes the cone to vibrate backwards and forwards

• The vibrations lead to sound waves being produced.

Reorder the following to explain why transformers are used in the National Grid.

• A step up transformer increases p.d. and decreases current

• Electricity is then transmitted at high p.d. and low current

• Low current means low power losses in the transmission cables

• ...because P = I²R

• ... so the system is more efficient: more power gets to consumers and less is lost from the lines as thermal energy

Reorder the following statements which explain the function of a transformer.

• An alternating current in the primary coil

• ... causes a changing magnetic field throughout the iron core

• This links to the secondary coil, which will cut the field lines due to the field changing

• A conductor which is cutting lines of magnetic flux will have a p.d. induced across it

• So a changing p.d. is induced across the secondary

Reorder the following statements which explain why a transformer won't work for DC current

• DC current will cause the primary coil to behave as an electromagnet

• So a constant field will be set up in the iron core

• This field links to the secondary coil, but it is not changing

• So the secondary coil does not cut any lines of magnetic flux

• So no p.d. is induced across the secondary coil

Reorder the following statements which explain the function of a microphone.

• Sound waves cause a diaphragm to vibrate.

• The diaphragm is attached to a coil, which also vibrates

• The coil is in the field of a permanent magnet

• So when the coil moves, a p.d. is induced across it

• This causes a current to flow in the circuit that the microphone is connected to.

A wire is moved through a magnetic field and a p.d. is induced across the wire. This is the ​ ​ ​ (a)   ​

• Generator Effect
• Motor Effect

Another name for the generator effect is ​ (a)  

• Electromagnetic Induction
• the motor effect
• dynamos and alternators

Reorder the following statements to explain the function of a motor.

• A coil of wire with a current passing through it has a magnetic field around it

• This interacts with a permanent magnetic field from a magnet near the coil

• This causes a force on the coil of wire

• The coil turns

• Finally, a commutator allows current to continue to flow into the coil as it spins

The motor effect states that a ​ (a)   conductor in a magnetic field will experience a​ (b)  

• current carrying
• copper
• thin
• force
• current
• field

A conductor moved through a (a)   will have a p.d. ​ (b)   across it. This is the ​ (c)   effect

• magnetic field
• region of space
• current
• induced
• produced
• created
• generator
• motor