How hot is it?

• Current – Voltage graphs

• Dependence of resistance on heat

• LDRs and thermistors

Current – Voltage graphsWhat is the component represented by this

graph? A resistor at constant temperature

V

I Draw another line for a resistor with lower resistance

Lower resistance Draw another line

for a resistor with higher resistance

Higher resistance

The current through a resistor (at constant temperature) is directly proportional to the voltage. The steeper the gradient, the lower the resistance

The gradient of the line is I/V, but

R = V/I

gradient = 1/R

Filament lampIs the filament lamp an Ohmic conductor? No, because the I – V graph is not a straight line, i.e. I is not directly proportional to V.

V

I The resistance of the metal filament inside the bulb increases as the filament gets hotter

Hot

Write on your graph “hot” and “cool” in the regions where the filament is hotter and cooler and explain why.

Hot

Cool

As more current flows, the metal filament gets hotter, so its resistance increases. That’s why the graph gets flatter.

DiodeIs the diode an Ohmic conductor? No, because the I – V graph is not a straight line, i.e. I is not directly proportional to V.

V

I There is current flowing only when the voltage is positive. This means that almost no current flows if the voltage is applied in the reverse direction.

Point on the V axis the voltage at which the current starts increasing.

0.6 V is the voltage at which the diode starts working, i.e. current flows through it. This voltage is called Activation Voltage.

0.6 V

Light Dependent Resistor LDRThe resistance in LDRs depends on how much light shines on them.

Light intensity

Resistance (Ω) When is the resistance higher?

Write on the light intensity axis bright and dark in the appropriate places.

When it is brighter!When is the resistance lower?

When it is darker!

Dark Bright

Light Dependent Resistor LDRThe resistance in LDRs depends on how much light shines on them.

Light intensity

Resistance (Ω) Choose the right ending. As the light increases…

1. the current decreases.

2. the current stays the same.

3. the current increases.

Dark Bright

Thermistor (Temperature Dependent Resistor)

The resistance in thermistors depends on the temperature.

Temperature

Resistance (Ω) In what conditions is the resistance higher?

Write on the temperature axis hot and cool in the appropriate places.

In cool conditions!

In hot conditions!

Cool Hot

In what conditions is the resistance lower?

Thermistor (Temperature Dependent Resistor)

The resistance in thermistors depends on the temperature.

Temperature

Resistance (Ω)

Cool Hot

Choose the right ending. As it gets cooler…

1. the current decreases.

2. the current stays the same.

3. the current increases.

Cell or Battery

Resistor

LDR

Diode

Thermistor

Filament lamp

Cell or Battery

Resistor

LDR

Diode

Thermistor

Filament lamp