RESISTANCE

WHAT IS RESISTANCE?

Resistance is the ability of a component in an electrical circuit to oppose current flow

EXAMPLES OF APPLIANCES

CONDUCTORS

A conductor is made of material that allows electric current to flow through it.

Good conductors offer some electrical resistance.

RESISTORS

A resistor a component that opposes the flow of the current in an electrical circuit.

There are two circuit symbols that can be used for a resistor

RESISTOR CONTROL ELECTRIC CURRENT Resistors are used to control the current

in an electric circuit. Resistors help maintain a safe current

within a component. Special resistors are made for creating a

very specific type of resistance. They maintain stable resistance value,

even when the temperature of the environment changes.

WHY ARE RESISTORS IMPORTANT?

Resistors provide useful energy transfer as they are also used to control the flow of current.

For example the element in an electric kettle turns electrical energy into heat energy that is used to boil water.

VARIABLE RESISTORS

some resistors do not supply a fixed resistance. they have a mechanism that that allows them to change their resistance.

For example. Dimmer light switches and volume control knobs on radios use such resistors.

They are called rheostats.

LIGHT-DEPENDENT RESISTORS

A light-dependent resistors are sensitive to the amount of light shines onto it.

It normally has a higher resistance in the dark than in the light.

it can be used to automatically switch the lights outside the on or of as it gets darker.

Symbol of rheostat

CONTINUATION

DIODES

Diodes are special electrical components that control the flow of electric current.

They provide high resistance the when the flow is in one direction and low resistance when the flow is in the opposite direction.

Diodes are not made from a mixture of metals like other resistors.

DIODES

A diode is made of two semi-conductors.

A light-emitting diode (LED) converts electrical energy into light energy.

Traffic lights have many circle LEDs3.

LIGHT-SENSITIVE DIODES

Light-sensitive diodes do the opposite of LEDs.

They convert light energy to electrical energy

The strength of the current in an electric circuit amperes (A).

The instrument is an ammeter.

FACTORS THAT AFFECT RESISTANCE IN A CIRCUIT

The different factors have an effect on the amount of resistance that a specific resistor offers.

The type of material The length The thickness temperture

1. TYPE OF MATERIAL

Good electrical conductors offer low resistance to the flow of charge.

For example, copper is a good conductor of electricity. We use copper for conducting wires and copper has a low amount of resistance.

Nichrome are also good electricity conductors but offer considerable electrical resistance.

They are used as resistors in devices where electrical energy has to be converted to other forms of energy.

SEMI-CONDUCTOR AND INSULATORS

Semi-conductors are substances that conduct an electric current under

certain condition

silicon

Insulators are substances that have a high electrical resistance

wood

MORE INSULATORS

2. LENGTH

Electric charges need more energy the further they move.

So charges need more energy to move through a longer wire than through a shorter one. The longer the resistor connected in an electrical circuit, the higher resistance of the circuit.

3. THICKNESS

The thicker the resistor or wire, the more the space for current to flow through and the lower its resistance.

4. TEMPERATURE

Electrical resistance varies with temperature.

For most metal resistors, the resistance increase s if the metal is heated.

It is difficult for chargers to move through heated conductors , because when heated the particles inside the conductors get more kinetic energy.

TEMPERATURE