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184 Science and Technology

An electric current flows in a loop – powering bulbs or

other electric. COMPONENTS. The loop is an electric

circuit. A circuit is made up of various components

linked together by wires. The current is driven around

the circuit by a power source, such as a. BATTERY.

A battery is a compact, easily transportable source of electricity. When a

battery is connected in a circuit, it provides the energy that drives the

electrons along in a current. Batteries contain chemical substances that

react together to separate positive and negative charges.

WHAT MAKES CURRENT

FLOW IN A CIRCUIT?

When a wire is connected to battery

terminals, electrons flow from negative to positive.

Unlike (opposite) charges attract, like (same) charges

repel. Electrons have a negative charge – they are

repelled from the negative and attracted to the positive.

WHEN DOES CURRENT FLOW IN A CIRCUIT?

Current only flows when a circuit is complete – when

there are no gaps in it. In a complete circuit, the

electrons flow from the negative terminal (connection)

on the power source, through the connecting wires

and components, such as bulbs, and back to the

positive terminal.

HOW DOES A BATTERY CELL WORK?

Inside a cell the electrolyte reacts with the electrodes,

causing electrons to move through the electrolyte

from one electrode to the other. One electrode gains a

negative charge and the other a positive charge. The

two electrodes are the positive and negative terminals.

WHAT IS INSIDE A BATTERY?

A battery is made of one or more sections or cells.

Inside each cell, two chemically active materials called

electrodes are separated by a liquid or paste called the

electrolyte. Small batteries may have just one cell.

Large, powerful batteries may have six cells.

WHAT IS AN ELECTRIC CURRENT?

Electric current is a flow of electric charge (usually in

the form of electrons) through a substance. The

substance or conductor that an electric current flows

through is often metal wire, although current can also

flow through some gases, liquids, and other materials.

PINBALL MACHINE 3

A pinball machine uses components wired into parallel

circuits to produce light, sound, and movement from

electricity. Switches control the circuits – when a

switch is off, no current flows. The steel ball turns on

switches so that bells ring, lamps flash, and springs

and flippers move.

BATTERY

1 IN SERIES AND IN PARALLEL

Circuits can be wired in two ways.

In a series circuit, current flows

to each bulb in turn. Both bulbs

are dimly lit. In a parallel circuit,

the current divides and flows

directly to both bulbs at the same

time. The bulbs are then brighter.

Circuits

4 SIMPLE BATTERY CELL

A simple cell can be made

by putting zinc and

copper electrodes into a

liquid electrolyte, such as

sulphuric acid.

Plastic

does not carry

current and can be

used to separate

different parts of

the circuit

Electrons flow from negative terminal

on battery, to each bulb in turn

Negative and positive

terminals wired to both bulbs

Electrons

flow

back to

positive

terminal

Zinc electrode

becomes negatively charged

Copper electrode

becomes positively charged

Flat disc

operates a

switch when

it is hit

Bubbles show

chemical action

PARALLEL CIRCUIT

Positive

terminal

Wires carry

current in circuit

Bulbs

brightly lit

SERIES CIRCUIT

Bulbs dimly lit

• 
  
  
  
  • – +
  
  
  
  

Sulphuric acid

Battery

circuits