 # LO: Understand the uses of electromagnets

## Presentation on theme: "LO: Understand the uses of electromagnets"— Presentation transcript:

LO: Understand the uses of electromagnets
Electromagnets differ from normal magnets in one major way! They are made by passing an electric current through a wire that has been wrapped around iron. The current creates a magnetic field and magnetises the iron core. When the current is turned off the iron loses its magnetism

LO: Understand the uses of electromagnets
Electric bell

LO: Understand the uses of electromagnets
Circuit breaker

LO: Understand the uses of electromagnets
Electrical relay

LO: Understand the uses of electromagnets
Scrapyard crane

LO: Understand how electromagnets can be used to make things move
The Motor Effect If a wire carrying a current is placed into a magnetic field, an interesting thing happens.

Fleming’s left hand rule
LO: Understand how electromagnets can be used to make things move Fleming’s left hand rule

LO: Understand how electromagnets can be used to make things move
Electric Motor 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!

LO: Understand how electromagnets can be used to make things move
Electric Motor Graphite ‘brushes’ are used to connect the split-ring to the battery. This is used because: Graphite is an excellent conductor It causes very little friction on the conducting ring

Electromagnetic Induction
Understand how generators create electricity ALL – State how electricity can be created MOST – Describe how electromagnetic induction can be increased SOME – Explain generators work in detail KEYWORDS: Electromagnetic induction, Generator, coil, wire, magnet

Electromagnetic induction
LO: Understand how generators create electricity Electromagnetic induction Electromagnetic induction is the term used to describe how electricity is created in a wire. This is ONE of only TWO ways that humans know how to generate electricity

Electromagnetic induction
LO: Understand how generators create electricity Electromagnetic induction By moving the magnet within the coil of wire, current can be induced within the current. Note, that the current is only induced when the magnet or coil is moving! How can the amount of current induced be increased? Increase the number of coils Increase the speed at which the magnet/coil moves Increase the strength of the magnet

LO: Understand how generators create electricity
Electric generators

LO: Understand how generators create electricity
True or false? Copy the true sentences and change the false sentences to make them true: Electricity is induced in a wire using a coil of wire and an electromagnet Electricity can only be generated when a magnet is stationary within a coil of wire The amount of electricity induced can be decreased by increasing the speed at which the magnet/coil of wire moves The amount of electricity induced can be increased by increasing the number of coils of wire

Transformers Understand how transformers work
ALL – State the function of step up and step down transformers MOST – Explain how transformers work and perform transformer calculations SOME – Explain why values from equations are just an approximation KEYWORDS: transformer, core, step up, Step down, primary, secondary, induced

Step-up and Step-down Why do transformers Increase and decrease
LO: Understand how transformers work Step-up and Step-down Transformers are an essential part of the national grid. They help to increase the voltage after the power station and help to decrease it again when it gets to your house. Why do transformers Increase and decrease The voltage in this way?

LO: Understand how transformers work

How do transformers work?
LO: Understand how transformers work How do transformers work? Discuss with the people on your table how transformers work. Remember the following: They only work with an a.c. current They need to have an iron core They use electromagnetic induction to work

LO: Understand how transformers work
The alternating current in the primary coil makes the iron core into an electromagnetic As the current is alternating, the magnetic field ‘moves’ and also changes direction This ‘moving’ magnetic field causes a current to be induced in the secondary coil If the number of coils on the secondary is higher, the potential difference will increase and it is a step-up transformer If the number of coils on the secondary is lower, the potential difference will decrease and it is a step-down transformer Make a flow diagram of how a transformer works in your book and draw a diagram to go with each stage

Transformer calculations
LO: Understand how transformers work Transformer calculations The following equation links together the voltage and number of coils in a transformer: 𝑉 𝑝 𝑉 𝑠 = 𝑛 𝑝 𝑛 𝑠 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

LO: Understand how transformers work
Example question A transformer has 400 turns on the primary coil and 200 on the secondary. If the primary voltage is 300v, what will the secondary voltage be?

LO: Understand how transformers work
Example question A transformer has 175 turns on the primary coil and 525 on the secondary. If the secondary voltage is 300v, what will the primary voltage be?

Transformer efficiency
LO: Understand how transformers work Transformer efficiency Transformers are extremely efficient devices.

Transformer efficiency
LO: Understand how transformers work Transformer efficiency Transformers are usually about 98% efficient. We can round this up and say that this is approximately 100%. Therefore, whatever power the device uses, it will output the same amount of power! Power in = Power out

Transformer efficiency
LO: Understand how transformers work Transformer efficiency Power in = Power out Vp x Ip = Vs x Is Vp = Voltage on primary coil (v) Vs = Voltage on secondary coil (v) Ip = Current on primary coil (A) Is = Current on secondary coil (A)

LO: Understand how transformers work
Example question A transformer has a primary voltage of 30v and a primary current of 2A. If the secondary voltage is 15v, what will the secondary current be?

LO: Understand how transformers work
Example question A transformer has a primary current of 10A. If the secondary voltage is 2v and the secondary current is 20A, what will the primary voltage be?

LO: Understand how transformers work
Example questions A transformer a primary current of 30A. If the secondary voltage is 10v and the secondary current is 2.4A, what will the primary voltage be? A transformer has a secondary voltage of 15v and a secondary current of 4A. If the primary voltage is 2v, what will the primary current be? A transformer has a primary voltage of 3v and a primary current of 30A. If the secondary current is 1.5A, what will the primary voltage be? A transformer has 300 turns on the primary coil, a primary voltage of 20V and a primary current of 5A. If the secondary coil has 200 turns, calculate the voltage and current on the secondary coil.