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What you need to know
Reflections and Exam tips
Electromagnetism - a magnetic field is created when an electric current flows through a wire.
The coiling of wire around a soft iron core creates a strong magnetic force which is used in electromagnets.
The current magnetises the iron core and when the current is turned off the iron loses its magnetism.
Electric bells and relay switches for example employ electromagnets which can be switched on and off.
The strength of an electromagnet can be increased by:
Applications of electromagnets
The ability of electromagnets to attract magnetic metals (iron, steel, nickel and cobalt) makes them useful in cranes to lift and drop iron and steel in scrapyards or recycling depots.
Outline of how an electric bell works
An electric motor uses the motor effect of electromagnets to create motion.
The force on one side of the wire causes it to move up
The force on the other side of the wire causes it to move down
The motor rotates.
Graphite ‘brushes’ are used to connect the split-ring to the battery because:
Electromagnetic induction is the term used to describe how electricity is created in a wire.
This is one of the ways that humans know how to generate electricity.
By moving the magnet within the coil of wire, current can be induced within the current.
However, the current is only induced when the magnet or coil is moving.
The current induced can be increased by:
Transformers are an integral component of the national grid.
Transformers increase the voltage after the power station and decrease the voltage when it gets to homes.
Transformers consist of the following:
Outline stages of how transformers work:
The following equation links together the voltage and number of coils in a transformer:
Vp/Vs = np/ns
Vp - Voltage on primary coil (v)
Vs - Voltage on secondary coil (v)
np - number of turns on primary coil
ns - number of turns on secondary coil
Transformers are usually about 98% efficient which means Power in = Power out.
You should be able to explain how electromagnetic appliances work by interpreting diagrams
You are required to know how four different components that use electromagnets work for your exam
As part of the GCSE course, you are required to know which way a wire placed into a magnetic field moves