Note: the circuit may contain devices for

controlling the amount of current; such as

Points to consider

(i) Rheostat

(ii) Switches

(iii) Resistors

When the switch 푆₂is closed while 푆₁is

open, no current flows voltimeter reads the

e.m.f of the cell

Also it may contain devices for measuring

current and p.d such as

When both switch 푆₁and 푆₂are closed, the

voltimeter reading decreases, therefore, the

meter reads the p.d across the bulb since the

current flows

(i) Ammeter; for measuring current

(ii) Voltimeter for measuring p.d

Electric circuit

Electric circuit is a closed path for electric

charge to flow through it.

Components of a circuit, includes

Fig: A complete circuit

(i) Source of moving charge (cell, battery or

generator)

TYPES OF ELECTRIC CIRCUIT

There are two types of electric circuit,

namely

(ii) Connecting wires made of conducting

material (usually copper metal)

(i)

Closed circuit

Open circuit

(iii) Bulbs

(ii)

(iv) Switches

(v) Resistors

Open circuit:

is the one which the

switch is open and no current is flowing

2. Cell: is a source of moving charge

Closed circuit: - is the one which the

switch is closed and the circuit is

complete

hence

the

current

flows

through the circuit

3. Lamp / Bulb: converts electrical energy

to heat and light

Lamp/ bulb

Circuit symbols

4. Resistor: Opposes the flow of current

A circuit symbol is a diagrammatic

Resistor

representation of the circuit components.

Example, the circuit symbol for a cell is

shown below.

5. Switch: Open and close a circuit

Switch

The following are some circuit symbols and

their functions.

6. Rheostat/ Variable resistor: Controls the

amount of current (for example, the

brightness of a lamp)

1. Wire: carry current from one point to

another point in a circuit.

Rheost

at

7. Galvanometer: Detects the presence of

electric current

circuit

F. Ammeter

G. Voltimeter

H. Switch

I. Lamp

(v) Opposes the flow of

current

Galvanometer

(vi) Converts electrical

energy to heat and light

J. Cell

8. Ammeter: Measures current

Answers

Ammeter

List

A

i

ii

E

iii

C

iv

v

vi

List

B

H

A

I

9. Voltimeter: measures the potential

difference (voltage)

Example 02 : Draw an open and closed

electric circuit using a bulb, battery, switch

and wire using circuit symbols.

Answers

Open circuit: is the one which the switch is

10. Capacitor: stores charges

open and no current is flowing

11. Fuse: breaks the circuit if excessive

current flows.

Example 01

Closed circuit: - is the one which the

Match the items in list A with the

corresponding responses in list B, the write

it letter besides the item number in the table

provided.

switch is closed and the circuit is

complete

hence

the

current

flows

through the circuit

LIST A

LIST B

(i) Detects the presence

of current

A. Resistor

B.

(ii) Controls the amount

of current

Galvanometer

C. Fuse

(iii) Breaks the circuit if

excessive current flows

D. Capacitor

E. Rheostat

(iv) Open and loses the

Example 03

State the functions of the following

components in electric circuits.

Step 3: Components connection

(i) Rheostat

(iii) Bulb

(ii) Switch

A single component is connected in series

with a source of e.m.f

(iv) Resistor

Answers: See your notes

Rules for constructing an electric circuit

1. Draw the circuit symbols first

Principle for constructing electric circuit

2. Using a ruler, draw all connecting wires

When drawing a circuit diagram, the

following steps should be followed.

3. Make all the connecting wires and leads

straight lines with corner angles of 90

degrees .

Step 1: Voltimeter connection

4. Do not cross any of the line representing

conducting wires

A voltimeter must be connected in parallel

with the components across which the

voltage is being measured

AMMETER

Ammeter is a device used to measure the

amount of current in a circuit

Characteristics of ammeter

1. Low internal resistance

An ammeter is designed with low resistance

so that it does not reduce the current flowing

in the circuit

2. Connected in series

Step 2: Ammeter connection

It must always be connected in series with

the components whose current is to be

measured.

Ammeter, which measure current, is always

connected in series with the circuit

component (s) to ensure that the current

flowing through the component (s) also

flows through, and is measured by, the

ammeter.

This ensures that, the current flowing

through the components also flows through,

and is measured by the ammeter