Electricity: Different Circuits
Objectives:
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Identify whether or not a simple circuit is complete
Learn how to use switches and other components in simple circuits
Observe the effect of changing the number of components in a circuit
Plenary
Using the plenary worksheet, pupils should identify the faults in the circuits, testing their
understanding of basic circuits.
In the first image, there is just one wire so the circuit is not complete. In the second image,
there is no battery/source of power. In the third image, there is a gap in the wire so the
circuit is broken. In the final image, the insulating eraser does not allow electricity to flow
through.
Using switches
Ask the pupils what a switch might do. They should consider the purpose of a light switch,
and may suggest that a switch turns a light on and off. Extend this by saying that a switch can
be used to turn any device on and off.
Draw a diagram of an incomplete circuit with a gap in a wire. Show that when the switch is in
the ‘on’ position, this gap is closed and electricity can flow through the whole circuit.
EXPERIMENT: Providing circuit parts including wires, batteries, bulbs and switches, allow
the students to design a simple circuit using a switch to turn a bulb on and off. This should be
similar to the circuits made in the previous lesson, but with a switch included between the
bulb and battery. Pupils should draw simple diagrams of their circuits (standard circuit
symbols do not need to be used).
Pupils must note:
When a switch is open, the circuit is incomplete. When the switch is closed, the circuit is complete
and the bulb can light up.
Brighter or dimmer?
Ask pupils to recall the role of the battery in the circuit. Ask what may happen if an extra
battery is added to provide more power.
EXPERIMENT: Pupils should use the circuits that they have already made. As they add a
second battery, they should carefully watch the effect that this has on the bulb and record
their observation. Then suggest that pupils return to using just one battery, but instead add a
second bulb and again, record their observations.
Encourage the pupils to suggest why adding an extra battery makes the bulb brighter while
adding an extra bulb makes the bulbs dimmer. They may be able to suggest that in the first
case, more power is being provided to the one bulb, while in the second case, the same
amount of power is being shared between two bulbs.
Pupils must note:
When an extra battery is added, the bulb becomes brighter. When an extra bulb is added, the
bulbs become dimmer.
Possible extra-curricular questions
How does the battery power the bulb/buzzer/motor?
The battery provides a ‘voltage’ or ‘potential difference’. When a voltage is applied to the
circuit, it causes a current. Every second, tiny charged particles called electrons travel
through the circuit, causing the bulb to light up. You can imagine the circuit as being a like a
water wheel at the bottom of a tilted passage; the battery is like the tilt, causing the water to
run and the water running through the wheel (causing it to move) is like the current.
How bright could a bulb get?
This depends on what kind of bulb you are using. Incandescent bulbs work by powering
(passing a current through) the filament, which becomes hot and glows. When too much
power (too high a current) is provided to a bulb, its filament will be destroyed.