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P5/6 science

All About Electricity

SAPSCSP5&6_W18/8

Taken from ScieNce PartNer: a complete Guide to Upper Block Science

Using Electricity In Different Ways

The brightness of a bulb depends on the amount of electrical current flowing through the circuit. The amount of electric current that is able to flow through the bulbs in a circuit is affected by some ways.

1 Increasing The Number Of Batteries In SeriesWe can adjust the brightness of a bulb in a circuit by increasing or decreasing the number of batteries used.

To make the bulb light up more brightly, we place more batteries in the electrical circuit. The batteries should be arranged in a series, meaning the positive terminal of one battery touches the negative terminal of another battery. This will increase the amount of electric current flowing through the circuit.

Batteries connected in a series

Alternatively, to make the bulb light up less brightly, we place fewer batteries in the electrical circuit. The electric current flowing through the circuit decreases, so the bulb does not light up as brightly as before.

However, the bulb will blow when we keep increasing the number of batteries in a circuit. This happens because there is too much electrical current flowing through the circuit. The voltage of the bulb cannot handle the increase in electrical current and the bulb fuses.

2 Increasing The Number Of Bulbs In Series

For bulbs arranged in series in a circuit with a fixed number of batteries, the greater the number of bulbs, the dimmer each of the bulbs will be as the electric current has to be shared between all the bulbs. If one bulb fuses, there will be a gap in the circuit and all the other bulbs will not light up.

The brightness of a bulb is compromised when there are many bulbs in a series.

The bulb is bright when one battery is used.

The bulb is brighter when two batteries are used.

The bulb is brightest when three batteries are used.


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3 Arrangement Of Bulbs In Series And In ParallelWhen we change the arrangement of the bulbs in a circuit, the brightness of the bulbs will be affected.

When two bulbs are connected in series, there is only one path for electricity to flow through the two bulbs. The amount of electric current that is able to cross each device depends on its resistance of each device and the current flowing through the circuit. When adding more components in a series circuit, the current flow decreases. Therefore, the bulbs light up but not so brightly.

A series circuit with one battery and two bulbs

In a series circuit, if a bulb fuses or a component is disconnected or damaged, there is a gap in the circuit. It becomes an open circuit, disrupting the flow of electric current.

In a parallel circuit, all the components have access to the full amount of electrical current available. If any one of the components of a parallel circuit stops working, the other components will still be able to carry on working. The bulbs stay bright even if more bulbs are added in parallel.

In a parallel circuit, each bulb is directly connected to the power source. Therefore, the bulbs arranged in parallel light up more brightly than when they are arranged in series.

A parallel circuit with one battery and two bulbs

4 Arrangement Of Batteries Connected In ParallelWhen the batteries are arranged in parallel, the bulbs in all three circuits will be of the same brightness. This is because the current flows through one loop at a time until the chemical potential in the battery has been used up before flowing through the next loop to make use of current from the second battery.


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Batteries connected in a parallel

However, the bulb in the third circuit shown above will remain lit three times as long as the bulb in the first circuit because it has three batteries to obtain its power from.

Circuit Tester And Circuit Card

A circuit tester is an instrument used to find out whether electricity is flowing through a circuit.

A circuit tester

A circuit card is a simple device to show if an electrical current flows between two points.

The bulb will light up if a circuit tester is used to test on paperclips A and E, E and F, or A and F.

The bulb will not light up if the circuit tester is used to test on clips A and D, A and B or any other pair that has no wires joining them together.

Using a circuit tester on a circuit card

same brightnesssame brightness same brightness

cardboard (backview)

metal paperclipD

E

F

A

B

C

switch


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Conductors And Insulators

A material that allows electricity to pass through it is a conductor of electricity.

Metals such as steel and iron are good conductors of electricity.

Carbon and water are non-metals which can conduct electricity.

A material that does not allow electricity to pass through it is a non-conductor or insulator of electricity.

In general, non-metals are insulators of electricity. Rubber, plastic and wood are insulators of electricity.

Most materials that can conduct electricity can also conduct heat.

Using Electricity Safely

Electricity is useful to us in many ways. However, electricity can also be dangerous. It can give us electric shocks or even start fires. To prevent such events from happening, we must observe certain safety precautions when handling electrical appliances.

• Do not touch electrical switches with wet hands. Since water is a conductor of electricity, theelectricity will pass through your body and give you an electric shock.

The presence of small amounts of salt in water is what makes it a conductor of electricity. Hence,seawater (because of its salinity) is a very good conductor of electricity. Pure water, on the other hand, is not a conductor of electricity. Unless you know for certain thatthe water you are using is extremely pure, you should always assume that water is conductiveand therefore, water and electricity should never mix together.

• Do not touch a person who is being electrocuted. Knock him away from the switch or appliancewhich is causing the electric shock with an insulator e.g. a wooden stick.

• Do not use a multiway adaptor and plug in many plugs into one socket. The overloading of thesocket may lead to overheating, sparking off a fire.

An overloaded socket with adaptors and plugs


P5/6 science

Electric Circuits

SAPSCSP5&6_W18/8

Taken from Nail thoSe McQs! PriMary ScieNce UPPer Block 5/6

1. Study the four electrical set-ups shown below carefully.

A.

battery

C.battery

B.

battery

D.

battery

Which set-up(s) would not cause both the light bulbs to light up at the same time?(1) A only(2) B only(3) C and D only(4) B, C and D only ( )

2. Study the electric circuit shown below.

S1 C1B2

B1

C2 S2

S3 B3

Key:S1, S2, S3: switchesB1, B2, B3: bulbsC1, C2: buzzers

Which of the following rows is correct?

Closed Open End results

(1) S2 S1, S3 Only B2 will light up.

(2) S2, S3 S1 Only B2 and B3 will light up and C2 will sound.

(3) S1 S2, S3 Only B1 and B2 will light up and C1 will sound.

(4) S3 S1, S2 Only B3 will light up.( )


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3. Which of the circuits shown below will not light up?

A.

B.

C.

D.

E.

(1) C only(2) A and C only(3) B and D only(4) C and E only ( )

Electric Circuits

Answers: 1. 3 2. 2 3. 4

SAPSCSP5&6_W18/8



P5/6 science

Electric Circuits

SAPSCSP5&6_W18/8


1. Study the electric circuit below.

Which circuit diagram represents the electric circuit shown above?

(1) (3)

(2) (4)

( )

2. A circuit has been set up and the results are shown in the table below.

SwitchesDid the bulb light up?

S1 S2

Closed Open No

Closed Closed Yes

Open Open No

Open Closed Yes

Which one of the following circuits will yield all the results in the table?

(1) S1

S2

(3) S1

S2

(2) S1

S2

(4) S1

S2

( )


P5/6 science

Electric Circuits

SAPSCSP5&6_W18/8


3. Which one of the following shows the correct connection between the filament and the metalcasing?

(1) (3)

(2) (4)

( )

Answers: 1. 2 2. 1 3. 2

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