Science notes, unit 5

Electricity

Textbook Science Year 5 (DLP), pages 115–144

What this chapter covers

You can name the sources of electrical energy and say what energy each one changes into electrical energy (5.1.1)
You can tell a series circuit from a parallel circuit and say how many paths the electric current has (5.2.1)
You can use symbols to sketch circuit diagrams of series and parallel circuits (5.2.2)
You can compare the brightness of bulbs in series and parallel circuits and explain why (5.2.3)
You can say how the number of dry cells and bulbs changes the brightness of bulbs in each type of circuit (5.2.4, 5.2.5)
You can predict what happens to the bulbs when a switch is opened in a series or a parallel circuit (5.2.6)
You can explain what affects the usage of electrical energy and how to save it (5.3.1, 5.3.4)
You can describe the effects of mishandling electrical appliances and the safety precautions to follow (5.3.2, 5.3.3)

Lights, fans, televisions and phone chargers all need electrical energy. In this unit you will find out where electrical energy comes from, how bulbs can be connected in a circuit, why some bulbs shine brighter than others, and how to use electricity wisely and safely.

5.1Sources of electrical energy

A source of electrical energy is something that changes another kind of energy into electrical energy. We use electrical energy to make light, heat and sound and to move objects.

A wind farm, wave generators and a hydroelectric dam, with a note that power plants use kinetic energy to turn turbines — Power plants use the kinetic energy of wind, waves and falling water to turn **turbines**, which generate electricity.

Source: Science Year 5 (DLP) textbook, p. 116.

Solar panels in a field under the Sun — A solar cell changes light energy from the Sun into electrical energy. It is used in satellites and calculators.

Source: Science Year 5 (DLP) textbook, p. 116.

Four sources of electrical energy: dry cell, dynamo, accumulator and generator, each with a picture of where it is used — Dry cell, dynamo, accumulator and generator.

Source: Science Year 5 (DLP) textbook, p. 117.

Source	Energy change	Where it is used
Power plant (wind, waves, hydroelectric)	Kinetic energy turns turbines and generates electrical energy	Supplies electricity to homes and factories
Solar cell	Light energy (Sun) to electrical energy	Satellites, calculators
Dry cell	Chemical energy to electrical energy	Toy cars; small and easy to carry everywhere
Dynamo	Kinetic energy to electrical energy	Bicycle light (the wheel turns the dynamo)
Accumulator	Chemical energy to electrical energy	Starting a car
Generator	Chemical energy of fossil fuels to electrical energy	Runs on fossil fuels to supply electricity

Did you know? Energy from the Sun is also called solar energy.

A cyclist pedals and the bicycle light comes on. Which source of electrical energy makes the light work? What energy does it change?

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A dynamo. It changes kinetic energy (the turning wheel) into electrical energy.

5.2Series circuit and parallel circuit

For a bulb to light up, the circuit must be complete: a dry cell, a closed switch, a bulb and wires joined in a loop with no gap. Bulbs can be connected in two ways.

Series circuit and parallel circuit

In a series circuit the bulbs are in one chain, so the electric current has one path to flow. In a parallel circuit each bulb is in its own branch, so the electric current can flow in more than one path.

A series circuit: a dry cell, a switch and two bulbs in one loop, labelled one chain of electric circuit — Series circuit: one chain, one path for the current.

Source: Science Year 5 (DLP) textbook, p. 118.

A parallel circuit: a dry cell with two branches, each with a switch and a bulb — Parallel circuit: two branches, so two paths for the current.

Source: Science Year 5 (DLP) textbook, p. 119.

	Series circuit	Parallel circuit
Arrangement of bulbs	One chain	Several branches, side by side
Paths for the current	One	More than one

Sketching circuits with symbols

A circuit diagram uses symbols instead of pictures of real parts. It is quicker to draw and shows the connections more clearly.

Table of components and their symbols: dry cell, two dry cells, open switch, closed switch, bulb — Components and their circuit symbols.

Source: Science Year 5 (DLP) textbook, p. 120.

Series circuit diagram
Circuit diagram: one dry cell, a closed switch and two bulbs A and B in one loop

Parallel circuit diagram
Circuit diagram: one dry cell with two branches, each with a closed switch and a bulb, C and D

How to sketch a circuit:

Draw the symbol of the dry cell.
Draw the symbols of the bulbs (and switches).
Join them with straight wires so the loop is closed. For a parallel circuit, draw the first branch, then the second branch beside it.

Use a ruler and keep every corner square. A gap in the wire in your drawing means an incomplete circuit!

The brightness of bulbs

A series circuit with bulbs A and B and a parallel circuit with bulbs C and D, one dry cell each — Same number of dry cells and bulbs. Bulbs C and D (parallel) are brighter than bulbs A and B (series).

Source: Science Year 5 (DLP) textbook, p. 123.

Series: one path, so the bulbs share the electric current. Each bulb is dimmer.
Parallel: more than one path. Each path receives the same amount of electrical energy, so each bulb is brighter than in the series circuit.

What changes the brightness?

Change	Series circuit	Parallel circuit
More dry cells	Bulbs get brighter	Bulbs get brighter
More bulbs	Bulbs get dimmer	No change: each bulb has its own branch

Three parallel circuits with one, two and three dry cells; the bulbs get brighter — In a parallel circuit, more dry cells means brighter bulbs.

Source: Science Year 5 (DLP) textbook, p. 127.

Three parallel circuits with one, two and three bulbs; all bulbs are equally bright — In a parallel circuit, more bulbs does not change the brightness of each bulb.

Source: Science Year 5 (DLP) textbook, p. 128.

A fair test: dry cells and brightness (series circuit)

Aim: to find out if the number of dry cells affects the brightness of the bulbs.
Hypothesis: as the number of dry cells increases, the bulbs light brighter.
Manipulated variable: number of dry cells (1, 2, 3).
Responding variable: brightness of the bulbs.
Constant variables: number of bulbs and type of circuit.
Conclusion: the hypothesis is accepted. As the number of dry cells increases, the brightness of the bulbs also increases.

Do not say "more bulbs make it brighter". In a series circuit more bulbs make each bulb dimmer, and in a parallel circuit more bulbs make no difference.

Which is brighter: one bulb in a parallel circuit with 1 dry cell, or the same bulb in a parallel circuit with 3 dry cells? And what happens to its brightness if you add another bulb in a new branch?

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Three dry cells is brighter (more electrical energy). Adding a bulb in a new branch does not change its brightness.

Closed switch, open switch

When a switch is open, the circuit is incomplete and the electric current cannot flow.

Series circuit. There is only one path. If either switch is opened, both bulbs go out.

Two series circuits with switches X and Y: in one X is open and Y is closed, in the other X is closed and Y is open; no bulb lights — Open either switch in a series circuit and all the bulbs stay off.

Source: Science Year 5 (DLP) textbook, p. 129.

Parallel circuit. Each branch has its own path. If a switch in one branch is opened, only the bulb in that branch goes out. The bulb in the other branch still lights up.

Two parallel circuits: switch X open so bulb A is off and bulb B is on; switch Y open so bulb B is off and bulb A is on — Only the bulb in the branch with the open switch goes out.

Source: Science Year 5 (DLP) textbook, p. 130.

One switch is opened	Bulbs in a series circuit	Bulbs in a parallel circuit
What happens	All the bulbs go out	Only the bulb in that branch goes out

Did you know? This is why, in the lights of a house, one blown bulb does not put out all the other lights. They are connected in parallel.

In a parallel circuit, switch S2 is open, but S1 and S3 are closed. Which bulbs light up?

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The bulbs in branches 1 and 3. Only the bulb on the branch with the open switch S2 is off.

5.3Using electrical energy wisely and safely

What affects the usage of electrical energy?

The more electrical energy we use, the more we pay on the electricity bill. Two things affect the usage: the type of electrical appliance we use and the duration (how long) we use it.

A house cut open showing ways to save electricity: use a fan, switch off lights when sleeping, switch off appliances not in use, close the refrigerator door — Ways to save electrical energy at home.

Source: Science Year 5 (DLP) textbook, p. 132.

Use a fan instead of an air conditioner.
Switch off the lights when you sleep and appliances that are not in use.
Do not leave the refrigerator door open for a long time.
Use the water heater less when you shower.
Dry clothes under the Sun instead of using a clothes dryer.
Unplug appliances that are not in use, and choose appliances that are energy efficient.
Use energy-saving lamps (LED lamp, compact fluorescent lamp) instead of filament lamps.

LED lamp and compact fluorescent lamp marked with ticks, filament lamp marked with a cross — Choose the LED lamp or compact fluorescent lamp, not the filament lamp.

Source: Science Year 5 (DLP) textbook, p. 133.

Green technology makes products in ways that do not cause pollution. The LED lamp is an example because it uses less electrical energy.

Mishandling electrical appliances

Electricity is useful, but mishandling electrical appliances is very dangerous. It can cause electrocution, a short circuit or a fire.

Effect	Examples of mishandling
Electrocution	Touching a switch or an appliance with a wet or damp hand. Putting an object that conducts electric current into a socket.
Short circuit	Using an appliance with a damaged wire. Connecting too many plugs into one socket.
Fire	Leaving a hot iron on clothes. Charging an appliance for too long.

An iron left on a cloth with smoke rising, and a phone left charging with smoke around it — Mishandling electrical appliances can start a fire.

Source: Science Year 5 (DLP) textbook, p. 136.

Safety precautions

A faulty appliance must be repaired by a certified person.
Your hands must be dry when you touch a switch.
Connect only one plug to one socket.
Turn off the switch before pulling the plug from the socket.
Replace a damaged wire with a new one.

A man repairing a wire with a screwdriver marked with a cross, and an electrician in a helmet marked with a tick

Many plugs in one socket marked with a cross, and one plug in one socket marked with a tick

Source: Science Year 5 (DLP) textbook, pp. 137–138.

Never touch a switch, plug or electrical appliance with a wet or damp hand. It can cause electrocution.

Name two safety precautions when you use electrical appliances.

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Any two: connect only one plug to one socket; turn off the switch before removing the plug; keep your hands dry; replace a damaged wire.