1.       F

If two magnets are attracting each other and one of them is turned the opposite way round, they will ………..

repel

2.       F

If a magnet is free to move it comes to rest pointing in a ………… direction

North-South

3.       F

The end of a magnet which points north  is called the n…….  s……… p…….... Like poles ……...; unlike poles ………...

north seeking pole, repel, attract

4.       F

Around a magnet there is a m………. f………. which will attract magnetic materials like i…… or s……..

magnetic field, iron, steel

5.       F/H

When can a coil of wire acts act like a bar magnet?

When an electric current flows through it

6.       F/H

What is the coil of wire from the above question called?

An electromagnet

7.       F/H

State three ways the strength of an electromagnet can be increased

* by placing an iron core inside the coil; * by increasing the number of turns on the coil; * by increasing the size of the current flowing through the coil

8.       F/H

What happens to an electromagnet if we reverse the current?

reverses the poles of the electromagnet.

9.       F/H

When a wire carrying an electric current is placed in a magnetic field, it may experience a f……..

force

10.    F/H

State two ways the above effect can be increased

* increasing the strength of the magnetic field; * increasing the size of the current.

13.    F/H

Explain how an electric motor works

A coil is placed inside a magnetic field. Current through the coil causes a 2nd magntic field.  The two fields creates the force which spins the coil around.

14.    F

What happens if a magnet is moved into a coil of wire which is part of a complete circuit?

A current is produced

15.    F

What is the above effect called?

Induction - the current has been "induced" in the coil

16.     

What changes if the magnet is now moved OUT of the coil (or if the other pole of the magnet is moved into the coil)

the direction of the induced current is reversed.

17.    F/H

Transformers  are used  to ....……………

… change the voltage of an a.c. supply

18.     

Transformers only works with d.c. electricity - True or False?

False - it's a.c.

19.     

At power stations, transformers are used to produce very high/low voltages before the electricity is transmitted to where it is needed through power lines. Local transformers reduce/increase the voltage to higher/lower levels before the electricity is supplied to consumers - choose the best answers

high, reduce, lower

20.    F/H

How does a generator work?

Electricity can be generated by rotating a coil of wire in a magnetic field or by rotating a magnet inside a coil of wire

21.    F/H

If a wire, or coil of wire 'cuts through' a magnetic field, a ……... is produced between the ends of the wire. This causes a…….. to flow if the wire is part of a complete circuit.

voltage, current

22.    F/H

The size of this can be increased in four ways - list them

* the speed of the movement increases; * the strength of the magnetic field is increased; * the number of turns on the coil is increased;  * the area of the coil is greater.

23.    H

Why do generators have slip rings or brushes?

They take the electric current from the coil without the connections becoming tangled up

24.    H

Explain carefully how a transformer works

A changing magnetic field will also produce an induced voltage in a coil. A.C. currents in the primary coil create a changing magnetic field - which induces a current in the secondary coil

25.    H

Why is electricity transmitted at high voltage?

The higher the voltage, the smaller the current needed to transmit energy at the same rate. Less energy is wasted by heating up the power lines.

26.    H

Write down a formula that shows how the voltages across the two coils in a transformer are related

eg. N1/N2  =  V1/V2