4. Current-Voltage Characteristics of a bulb
In this experiment you are going to investigate how the current through a bulb changes according to the voltage across it.
Current (amp) Voltage (Volt) V A
To get negative currents and voltages,
use reverse polarity on the battery pack

5. A graph of the results should look like this
Hot filament
*resistance increases
*current does not increase in proportion to voltage
*filament is non- ohmic
Current /A
BULB
Voltage / V
Cold filament
*constant resistance
*current is directly proportional to voltage.
*The metal filament inside the bulb follows ohms law

6. In the forward direction the line curves towards the current axis.
(What is happening to the resistance?)
Diodes are non- ohmic conductors
DIODE
1.2
What is the resistance of the diode when the voltage is 2V?
In the reverse direction, current flow is very, very low.
Is the resistance of the diode high or low?
R = V / I
R = 2 V / 1.2 A
R = 1.7 Ω

8. Thermistor
A thermistor’s resistance decreases as the temperature rises.
USE: temperature sensor, fire alarm

9. Light dependent resistor (ldr)
An LDR’s resistance decreases as the amount of light falling
on it increases USE: street lights

10. What do the current-voltage graphs look like for a thermistor and an LDR?
The line is straight so the resistance is constant for a set temperature.
High temperature
Current (A)
Low temperature
But at lower temperatures the resistance is higher (so the current is lower)
Voltage (V)
The line is straight so the resistance is constant for a set light level.
Current (A)
Voltage (V)
Bright light
Dim light
LDR
But at lower light levels the resistance is higher (so the current is lower)