4.2 - Resistance

Resistance

Opposition to the flow of current

Ohms law

At CONSTANT TEMPERATURE the current is directly proportional to pd

Resistor IV graph

Lamp IV graph

Diode IV graph

Thermistor IV graph

Explain filament lamp IV graph

As the current increases the temperature of the lamp increases.

Higher temp can cause increase in resistance

What happens to a thermistor and LDR

As temperature rises resistance decreases

LDR circuit symbol

LDR resistance light intensity graph

What causes a wire to heat up?

As a free elctronss move through the metal wire they collide with ions which get in their way as a result of they transfer some KE on collision which cause some electrical heating

What causes resistance

Ions resisting the flow of charge

Formula for resistinace (w Resistivity)

How does wire thickness impact resistance

The thicker the wire the smaller its resist

What happens to number density of charge carriers in semiconductors?

It increases with increasing temperature but only for NTC semiconductors

What does NTC stand for

Negative Temperatyure Coeffcient

What does a thermistors resistance vary with

Temperature

Thermistor resistance temperature graph