Class exercise 1

Find the equivalent resistance of the following circuit.

Class exercise 2

Find the equivalent resistance of the following circuit.

Class exercise 3(P.160#5a)

2

1

4

3

A B

D C

The resistance across AB is:1

4 3 2 9

10

234

1

1

1

R

1

Class exercise 4(P.160#5e)

2

1

4

3

A B

D C

The resistance across AC is:1

4 3

2

21

10

34

1

21

1

R

1

Class exercise 5(P.160#6)

Class exercise 6e.m.f. of the battery = 12 V

100

100

100 X Y

Z

(a) What is the potential difference across X and Z?

(b) What is the potential difference across X and Y?

(c) What is the potential difference across Y and Z?

Class exercise 6e.m.f. of the battery = 12 V

100

100

100 X Y

Z

(d) What is the current flowing out from the battery?(e) What is the current flowing from X to Y?

(f) What is the current flowing from Y to Z via the

upper and lower resistor?

Class exercise 7e.m.f. of the battery = 12 V

120

200

300 X Y

Z

(a) What is the current flowing out from the battery?(b) What is the current flowing from X to Y?

(c) What is the current flowing from Y to Z via the

upper and lower resistor?

Class exercise 8(P.161#9)

Electrical Power

The rating on a lamp is

‘220 V / 1000 W’.

What does it mean?

R

VRIVIP

22

Electrical Power

This means when the lamp is operated normally, that is, when the voltage supplied to the lamp is 220 V, then the lamp consumes electrical energy at a rate of 1000 W.

Under normal state, the electrical energy consumed by this lamp in 1 hour is 1 kWh.

1 kWh = 1000 3600 J = 3600000 J

L,N,E

socket

Green and yellow

blue

brown

Ring circuit

N

E

L

Fuses

Symbol for fuse

Fuse wire is connected with the live wire.

When the current is above the safety limit, the fuse will blow and the live wire is cut off from the mains supply.

Symbol for double insulation

Symbol for double insulation

Class exercise 10

Class exercise 11(P.185#9)

1I 2I

I

Class exercise 12P.185#11)

The lamps are connected in parallel instead of in series for:

(1) The lamps can be operated separately.

(2) If one lamp is damaged, the other

lamps can still function.

Earthing

Earthing

Overloading

Do not overload a universal adaptor.

Damaged wires

Do not touch the damaged wires. Repair the damaged wires.

Damaged wires

Do not pull a plug out from a socket by holding the wire only

Don’t touch the switch with wet hands

Do not operate a switch with wet hands.

Don’t use electric appliances in bathroom

Do not use electric appliances in the bathroom via an extension cable.