1. KS4 Electricity – Uses of Electromagnetism

2. Relays
A relay allows one circuit to control another circuit – turning it on and off.
What will happen when the switch in circuit A is closed?
The coil becomes an electromagnet as electricity flows in circuit A. N
Steel switch
Coil
The coil attracts the steel switch in circuit B and completes the circuit. M S
Electricity flows in circuit B and the motor now works. B A

3. Circuit Breakers Circuit breakers are also based on this principal.
The current flows through a coil of wire.
If the current becomes dangerously high, the coil creates a magnetic field strong enough to…
…cause the iron or steel switch to open…
…which breaks the circuit.

4. Using electromagnets in switches
Electromagnets can be used to OPEN switches or to CLOSE switches.
There could be one of these circuit breakers in your laboratory!

5. Loudspeakers
Varying an AC through the wire makes the cone of the loudspeaker vibrate back and forth. The vibrations cause sounds.

6. Using electromagnets Circuit breakers Relays Loudspeakers
Convert electrical energy into sound energy
Using one circuit to turn another circuit off and on
Used to break a circuit if the electrical current is too high
Circuit breakers
Relays
Loudspeakers

7. A current carrying wire in a magnetic field
We know that a wire carrying a current can be made into an electromagnet. Consequently, such a wire will behave like a magnet. If this wire is placed near a permanent magnet, it will experience a force.
We can use Flemings left hand rule to predict the direction of this force. In fact, we can also use it to predict the direction of any one of the following (if the the direction of the other two is known).
the direction of flow of conventional current.
the direction of the magnetic field (from north to south).
the direction of the force exerted on the wire.

8. Current (second finger)
Flemings Left Hand Rule
Force (thumb)
Field (first finger)
Current (second finger)

9. Animation of a current carrying wire in a magnetic field

10. How could you increase the strength of the force?
More current
More resistance
Stronger
magnetic field
TRUE/FALSE

11. The coil will spin in opposite direction.
The DC Motor
Uses Motor effect principle.
How does it work?
Each side of coil pushed in opposite direction due to motor effect.
This results in the coil rotating. N S
What happens if you reverse the direction of current or magnetic field?
The coil will spin in opposite direction.

12. Electromagnetic induction
What will happen if you move a magnet into a coil of wire?
A current is induced in the coil.
Only when the magnet is moving.

13. Stationery magnet What happens when the magnet is in the coil?
Nothing!!
A current is only induced when the magnet is moving.

14. Electromagnetic induction
What will happen if you move the magnet out of the coil of wire?
A current is induced in the coil.
This time in the opposite direction.
If you reverse the direction of the movement, then you reverse the direction of the current.

15. What type of current is this?
AC or DC?
What will happen if you move a magnet in and out of the coil repeatedly?
A current will be induced in the coil, the current will flow in one direction and then reverse and flow in the opposite direction.
What type of current is this?
Alternating current

16. Increasing the size of the current
How can you increase the size of the current?
more coils
stronger magnetic field
faster movement

17. Stronger magnetic field
AC generator
What are the four ways you can increase the current from an AC generator?
1. _____________________
2. _____________________
3. _____________________
4. _____________________ ?
Faster movement
Stronger magnetic field
More coils
Larger area of coils

18. Transformers What is a transformer? Where are transformers used?
What do we call a transformer that increases voltage?
What do we call a transformer that decreases voltage?
A device used to increase or decrease voltage
On the National Grid, household appliances
STEP-UP Transformer
STEP-DOWN Transformer

19. How electricity gets to your home….
Power station
Step-up transformer
National Grid
Step-down transformer
Homes, businesses and factories etc

20. Why bother with transformers?
When electrical current flows you get f_____ in the conductor. With friction you always get h___. This heat is wasted e____. You get more wasted energy at low v______ than high voltages. So the current is increased in voltage before it is transferred to the N_____ G__. In this way less energy is lost. Then, when it gets to your home, a school or a factory, the voltage is stepped d___.
riction
eat
nergy
oltages
ational rid
own

21. More/less turns on the primary coil than the secondary coil.
Step-down
More/less turns on the primary coil than the secondary coil.
Primary
Secondary

22. More/less turns on the primary coil than the secondary coil.
Step-up
More/less turns on the primary coil than the secondary coil.
Primary
Secondary

23. Transformer calculations
The size of the output voltage depends upon the ratio of the turns on the primary and secondary coils.
Guess what? There’s a formula (it is Physics after all!) -
V1 = N1
V2 = N2
V – voltage N - number of turns

24. Transformer Question 1
A transformer has 200 turns on its primary coil and 50 turns on its secondary coil. The input voltage is 920V.
Is is a step-up or step-down transformer?
What is the output voltage?
Step-down
230V

25. Transformer Question 2
A transformer has 100 turns on its primary coil. It has an input voltage of 35V and an output voltage of 175V.
Is is a step-up or step-down transformer?
How many turns are on the secondary coil?
Step-up
500 turns

26.  The magnetic field is increased The voltage increases
What happens if you reverse the direction of current in an electromagnet?
The magnetic field is increased
The voltage increases
The current increases
The direction of the magnetic field is reversed 

27.  The current is increased The magnetic field is reversed
What happens if a wire carrying a current is placed in a magnetic field?
The current is increased
The magnetic field is reversed
The magnetic field is increased
The wire will experience a force 

28. Which below will not increase the strength of an electromagnet?
More coils
More current
Less current
Iron core 

29. Which use of electromagnets is similar in function to a fuse?
Relays
Transformer
Circuit breaker
Loud speaker 

30. Which of the following is not a use of electromagnets?
Fridge magnets
Loud speakers
Relays
Circuit breakers

31. A transformer has 30 turns on its primary coil and 240 turns on its secondary coil. If the output voltage is 128V, what is the input voltage? 8V
16V
1024V
512V 