8. Should not be left in a discharged state for

a long time

The current showing through the cell is the

same as for one cell. The total voltage across

the equal to the sum of the voltage of the

individual cells

9. When recharging direct current at low

current

should

used

AND

NOT

alternating current.

Use of lead - acid batteries

The following are some uses of the lead –

acid batteries

1. They are used to provide power in motor

vehicle

2. They are used to provide energy to power

domestic appliances such as radio, television

and lighting fixture.

(a) When cells are arranged in series

3. They are used together with solar panel to

convert solar energy to electrical energy.

oTotal E.M.F of the arrangement is the

sum of the separate E.M.F

퐸_푇= 퐸₁+ 퐸₂+ 퐸₃

Example 01

When the car battery is said to be sulphated?

oInternal resistance of the battery is the

sum of the internal resistance of the

separate cells

Answers

푟_푇= 푟 + 푟₂+ 푟₃

The car battery is said to be sulphated when

it is fully discharged.

Parallel arrangement

When the cells are placed in parallel all the

positive terminal are connected together.

Any point of the positive side of the battery

can serve on the positive terminal of the

battery.

ARRANGEMENT OF CELL

Cells are often used in combination. A

battery is formed when two or more cells

are connected together. There are two ways

of combining two or more cells. These are

The total voltage of all cell in parallel is the

same as that of a single cell.

series

combination

and

parallel

combination.

Series Combination

When cell is placed in series the positive

terminal of one cell is connected to the

negative terminal of another cells.

(a) State the type of charging current,

approximate value of the current and

the approximate e.m.f of the cell

Answers

Direct current (d.c) of approximately

2A. The e.m.f of a fully charged

accumulator is 2.2V.

(b) Mark the plates A and B, positive (+)

or negative (-) as they should be.

(b) When cells of equal E.M.F’s and

internal resistance are connected in

parallel:

Answers

A is negative B is positive.

o The resultant E.M.F is the same as the

E.M.F of one cell

Remember that while charging an

accumulator, the positive lead from

the charger is connected to the

positive terminal of the accumulator.

퐸_푇= 퐸₁= 퐸₂= 퐸₃= 퐸

current is passed for 5 – 10 minutes?

Answers

o The total internal resistance is calculated

The positive plate B where the current enters

the accumulator turns deep brown in colour

due to the formation of Lead (IV) oxide on

its surface. Grey spongy lead is formed at

the negative plate A.

using the formula of resistance in parallel

푟_푇

푟

푟₂

푟₃

Example 01

Example 02

The figure below shows the circuit when

charging simple lead acid

accumulator.

Explain why lead – acid accumulators are

used in car batteries rather than dry cells.

Answer

–

(i) It has a very low internal resistance

which means that the battery can supply a

large current without an appreciable drop in

p.d across its terminals.

(ii) Besides supplying a large current, it can

be re – charged without loss of materials.

(iii) It does not require a depolarizer like the

dry cell. The dry cell depolarizes in a short

time and has internal of about a few Ohms.

This means that it can provide small current

at intervals. Hence a dry cell battery cannot

be used to run a car.

The 20V supply and accumulator should

be connected such that their e.m.f. are

opposed.

So effective voltage = 20 – 12 = 8V

Charging current = 2A

Resistance required = 4 ohms.

Answers

Example 03

Nickel – cadmium accumulators are used for

emergency lighting e.g. in hospitals rather

than the lead – acid accumulators. State the

advantages of an alkaline cell over the acid

one.

Here the charging current is 2A; Time

rated is 72hours; so it will be fully

charged in 36 hours

Example 05

A car battery is 12V, eight dry cells of 1.5V

connected in series can give 12V but such

cells are not suitable in starting a car. Why?

Answers

Alkaline (Nickel – Cadmium) accumulators

are more expensive than the lead – acid type

but they

Answers

To start a car, a very high current is

required. When eight dry cells are joined in

(i) Have a very much longer life than the

lead – acid ones,

series

the

internal

resistance

the

combination of the cells becomes very high.

Due to high value of internal resistance, the

current that can be drawn from the cells is

very small to start the car.

(ii) Give larger currents for longer periods

(iii) Can be left unused for months without

any harm

Example 04

Example 06

(a)

accumulator

negligible

Give a reason why the caps of the cells of a

lead – acid accumulator is opened when

charging the battery?

resistance and normal charging rate of

2A is marked 12V 72Ah (ampere hour).

What does this mean?

Answers

This accumulator can be charged on a 12

Volt – supply. 72Ah means the cell will be

fully charged in 72 hours if charging current

is 1ampere.

The caps of the cell are opened to allow

gases to escape from the battery.

Example 07

When the lead acid accumulator does is said

to be sulphated?

(b) If a 20V supply is used for charging,

what is the accumulator to be added to

the circuit?

Answers

A lead acid accumulator is said to be

sulphated if it is no longer functioning, that

is when it cannot be recharged

Answers

Current electricity is used in transportation

to power various electric vehicles. For

example, standard gauge railway trains use

electricity for efficient and eco – friendly

travel.

Example 08

How would you test whether a car battery

needs recharging? (Give three points).

Tyr this

Answers

1. A wire of resistances 12 Ω and 36 Ω are

connected in parallel. Two such

(i) By measuring the relative density of the

acid using a hydrometer. If the relative

density is low, the battery needs to be

recharged

combinations are put in series. By drawing

the circuit diagram, calculate the effective

⟦

⟧

resistance. 퐀퐧퐬: ퟏퟖ 훀

2. A wire of resistance 72 Ω is cut into three

pieces of equal length which are connected

in parallel. By drawing the circuit diagram,

calculate the effective resistance of the

(ii) By measuring the e.m.f of the battery, if

the. e.m.f is low, then the battery needs to be

recharged

⟦

⟧

combination. 퐀퐧퐬: ퟖ 훀

3. You have been provided with three (3)

identical resistors of 36 Ω. Show by drawing

the circuit diagram, how would you combine

all of them to get effective resistance of;

(iii) By measuring current delivery by the

battery, if the current is low, then the battery

needs to be recharged.

(a) 24 Ω

(b) 54 Ω, In each case calculate

2.7 Uses of current electricity

the value of the effective resistance of the

combination to support your answer:

1. Domestic uses of current electricity

Ans:

(i) Electricity is essentially for domestic

tasks like cooking, preserving food, and

doing laundry.

( )

a 2 is in series and placed in paralle to the third

⟦

⟧

( )

b 2 in paralle and placed in serie with the third

(ii) It power appliances such as stoves,

refrigerators, washing machines, and irons.

4. Why eight dry cells each of e.m.f 1.5 V

cannot be used in a car to start the starter

motor in the ignition system of a car?

(iii) It also provides lighting, entertainment

through TV and computers and comfort

using fans, heaters and air conditioners.

Answers: dry cells in series give a large

internal resistance and the current drawn

will be too low.

2. Industry use of current electricity

5. One 4 Ω and two 2 Ω resistors are

available. All three are to be connected

together in different arrangements such that

the total (resultant) resistance is:

Industries use current electricity to power

machines and equipment essential for

manufacturing and production. For example,

textile mills use electric looms, car factories

operate robotic arms and conveyor belts, and

food processing plants run mixers and

packaging and packaging machines.

(i) Less than 2 Ω

(ii) More than 4 Ω but less than 8 Ω

Draw a diagram of each arrangement and

calculate the total (resultant) resistance in

each case.

3. Transport use of current electricity