Circuit components AYr1

Circuit components definitions, symbols (British) and their graphs

Thermistor (negative coefficient)

• high temperature, low resistance

• low temperature, high resistance

• made from semiconducting materials

• used in sensor circuits

Rheostat

c

Potensiometer

d

Sensor circuits definition

A circuit that uses a sensor (light dependent resistor/thermistor) to trigger another component in the circuit

Light emitting diode

Same in all respects as a standard diode, only it emits light when a current goes through

Light dependent resistor

• A resistor whose resistance depends on the amount of light incident on it.

• It is a negative coefficient semiconducting material - more light means it releases more delocalised electrons, decreasing its resistance.

• Used in sensor circuits (e.g. triggers when the sun goes down)

Switch

• breaks the circuit when open

• must be closed for current to flow

Cell and battery

• Provide the energy in DC circuits

• Have a positive and negative terminal

• Conventional flow of current from positive to negative

• Have an EMF and a terminal P.D

• a battery is mulitple cells linked together (in series)

Lamps/bulbs (filament)

• Convert electrical energy to Light and Heat

• Resistance increases with the current and the voltage because their temperature rises

voltmeter

• Measure the P.D. between its two terminals 

• Always connected parallel with the component whose P.D. we wish to measure

• Has practically infinite resistance (current never flows through it)

ammeter

• Measures the current through a component

• Always connected in series with the current we want to measure

• Has practically zero resistance (does not affect the flow of current)

fixed resistor

• Obeys Ohm’s Law

• R only depends on temperature

• Energy transferred to it turns to heat and dissipates to the surroundings (air, water etc)

variable resistor

• A resistor whose resistance we can vary at will within certain limits

• Used in light dimmers and many other applications

motor

• A component which uses the energy transferred to it to generate motion

• Motion is rotational e.g. axles, winches, washing machine drums, mixers etc

• (more in YR13)

diode

• Only allows current to go through in a given direction (that of the arrow)

• Has a cut-off voltage - i.e. will not conduct current below a certain value even if it is in the right direction

heater

• Similar to resistors, it generates heat when an electric current flows through

• E.g. electric blankets, rear car window resistors etc

cut off voltage

• the component will not conduct current below a certain value (even if in correct direction for a diode)

• seen in diodes (not sure about other components)

equivalent resistance

total electrical resistance caused by all of the resistors in the circuit acting together against the voltage source