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Electrical Circuits 02
The plastic coating on electrical wires is an insulator.

Electrical Circuits 02

Test yourself on electrical circuits in this KS3 Science quiz. Insulators and conductors are words used in relation to electrical circuits. An insulator is a substance that does not allow electricity to pass through. It is useful for making sure that electricity does not get to places where it should not be! Examples of materials that are insulators are plastics and ceramics. Plastics are flexible and can be used on the outside of electrical wires, which need to be able to bend. Ceramics are brittle and inflexible. They are used on electricity pylons to keep the high voltage lines from touching the pylon. Metals are good conductors of electricity, some are better than others. Copper is a much better conductor than steel and is more malleable (bendy) so is a good choice for making wires. But copper is too heavy and weak to use for the large overhead wires that are used to transfer electricity around the countryside so aluminium is used instead.

Components in an electrical circuit can be joined in two ways, series or parallel. In series, they are one after the other (like a TV series, each episode comes after the previous one). If one component in a series circuit breaks, the whole circuit stops working. In a parallel circuit, if one breaks, the rest of the circuit still works.

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Two identical bulbs are in parallel in a complete circuit. If one breaks:
the other bulb is brighter
the other bulb is dimmer
the other goes off
the other stays on
This is a benefit of a parallel circuit, it is usually easier to find out which component has broken as the rest still work
Which of the following statements is true?
A flow of electrons around a circuit is called an electric current
A switch only turns the current off
An open switch allows a small amount of current through it
Two identical bulbs in a series circuit are brighter than one
It can sometimes be helpful to think of electricity flowing round a circuit like water through pipes
Which of the following statements is true?
A voltmeter is connected in series to measure voltage.
An ammeter is connected in parallel to measure current.
Different sized bulbs in parallel have the same current flowing through them.
In a parallel circuit with four identical bulbs, the current is shared equally between them.
If the four bulbs were NOT identical, the current would still be shared out, but not equally
Three identical bulbs are in parallel in a complete circuit. The current in each bulb:
is different in all bulbs
is greatest in the bulb nearest the battery
is the same
is three times the current flowing from the battery
The current in each bulb is a third of the total current flowing round the circuit
Wires are usually coated in plastic because:
plastic can be lots of different colours
plastic helps the wires bend
plastic helps the wires conduct electricity
plastic is an insulator
Wires used to be covered with rubber as an insulator but rubber perishes faster than plastic
If the size of a battery in a complete circuit is increased:
the current decreases
the current increases
the current stays the same
the voltage stays the same
An increase in voltage will increase the current flowing in a circuit (if nothing else is changed)
Two identical bulbs are in parallel in a complete circuit. A third identical bulb is connected in parallel. What happens?
All the bulbs are dimmer
All the bulbs are the same brightness
The third bulb is brighter
The third bulb is dimmer
Adding identical bulbs in parallel uses more current but brightness stays the same
Wires are normally made from copper. This is because:
copper has a high resistance
copper is a very good conductor of electricity
copper is cheap
copper is expensive
It is also very malleable and can therefore easily be bent to go round corners
The current in a series circuit containing two bulbs:
is larger between the bulbs
is larger nearer the battery
is smaller nearer the battery
is the same at every place in the circuit
This is an important point to remember about a series circuit
Two bulbs are in series in a complete circuit. If the voltage is increased:
the bulbs get brighter and the current decreases
the bulbs get brighter and the current increases
the bulbs get dimmer and the current decreases
the bulbs get dimmer and the current increases
The number of bulbs was not changed so there is more current flowing and the bulbs are brighter
Author:  Sue Davison

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