Circuits 3. Resistance

A resistor opposes current by converting the electrical energy in a circuit into heat energy.

Variable resistors have many practical applications including volume controls, eg on a radio, and speed controls, eg on a mixer or a drill.

There is usually a dial or sliding switch on the variable resistor which rotates or slides

If you increase the voltage across a component, there will be more current in the component. Too high a voltage and the bulb will blow.

If you increase the number of lamps in a series circuit, there will be less current. The lamps resist the current, so if you put more lamps into the circuit, there is more resistance.

INCREASING THE RESISTANCE .

The resistance increases when you add more components in series. For example, the resistance of two lamps is greater than the resistance of one lamp, so less current will flow through them.

A variable resistor can be set to change resistance up or down

A graph of current against potential difference shows you how the current flowing through a component varies with the potential difference across it.

A filament lamp is a common type of light bulb. It contains a thin coil of wire called the filament. This heats up when an electric current passes through it, and produces light as a result.

The resistance of a lamp increases as the temperature of its filament increases. The current flowing through a filament lamp is not directly proportional to the voltage across it

Diodes are electronic components which can be used to regulate the potential difference in circuits

A diode has a very high resistance in one direction. This means that current can only flow in the other direction.

Thermistors are used as temperature sensors, for example, in fire alarms. In the most common type of thermistor, the resistance decreases as the temperature increases:

at low temperatures, the resistance of a thermistor is high and little current can flow through them

at high temperatures, the resistance of a thermistor is low and more current can flow through them

LDRs are used to detect light levels, for example, in automatic security lights. Their resistance decreases as the light intensity increases:

in the dark and at low light levels, the resistance of an LDR is high and little current can flow through it

in bright light, the resistance of an LDR is low and more current can flow through it

Light-emitting diodes and lamps produce light when a current flows through them in the forward direction.

LEDs and lamps are often used for indicator lights in electrical equipment, such as computers and television sets. As LEDs use a much smaller current than other types of lighting.