Chapter 8: Electricity

Diodes

________ have an extremely high resistance in one direction but a low resistance in the other.

Variable resistors

________ (rheostats) are used for varying current.

Broken

________ strands mean that a wire will have a higher resistance at one point.

hi fi equipment

In ________, rotary (circular) variable resistors are used as volume controls.

Fuse

________- this is a thin piece of wire which overheats and melts if the current in circuit is too high.

Insulators

________ are materials that hardly conduct at all.

Semiconductors

________ are ‘ ‘ in between materials.

electrical thermometers

Some ________ use a thermistor to detect temperature change.

electrical equipment

Water will conduct a current, so if ________ gets wet, there is a risk that someone might be electrocuted.

electronic circuits

They can be used in ________ which switch lights on and off automatically.

ohmic conductor

In a(n) ________, the current is directly proportional to the voltage (ie.

materials

Conductors are ________ that let electrons pass through them.

metal body

If the live wire comes loose and touches the ________, a current immediately flows to earth and blows the fuse.

zero voltage

In many circuits, it is kept at ________ by the electricity supply.

Power

________ is the rate at which energy is transferred.

RCD

With lawnmowers and hedge trimmers, a plug- in ________ can be used to avoid the risk of electrocution.

Resistors

________ are specially made to provide ________.

Flow of charge

________ is an electric current.

Material

________- a nichrome wire has more resistance than a copper wire of the same size.

Temperature

________- for metal conductors, resistance increases with ________.

simple circuits

In ________, they reduce the current.

Free electrons

________ make metals good thermal and electrical conductors.

temperature

For semiconductors, it decreases with ________.

Their electrons are tightly held to atoms and are not free to move

although they can be transferred by rubbing

Length

doubling the length of a wire doubles resistance

Cross-Sectional Area

halving the "end on" area of a wire doubles its resistance

Material

a nichrome wire has more resistance than a copper wire of the same size

Temperature

for metal conductors, resistance increases with temperature

Live Wire

this goes alternately negative and positive, making the current flow backwards and forwards in the circuit

Neutral Wire

this completes the circuit

Switch

this fitted in the live wire

Fuse

this is a thin piece of wire which overheats and melts if the current in circuit is too high

Earth Wire

this is a safety wire