Explaining the shape of the current-voltage graph for the bulb Current (A) Voltage (V) Cold metal = low resistance Hot metal = high resistance If the metal is heated, the metal ions will vibrate more. This means that there is a greater chance of an electron bumping into a metal ion and so the flow of electrons is reduced. i.e. the resistance is increased. A low resistance means that the electrons can move easily, therefore the current will be high.

The Diode The diode is a non-ohmic conductor. It allows the current to flow in one direction only. Doesn’t allow the current to flow (has infinite resistance in the reverse direction) Allows the current to flow in the forward direction diode Current (A) Plotting a current-voltage graph for a diode produces this shape line Voltage (V)

which bulb will light up (notice the position of the diodes). A B C Circuit 1

answer A B C Circuit 1 A & B only

which bulb will light up (notice the position of the diodes). A B C Circuit 2

answer A B C Circuit 2 None of them

which bulb will light up (notice the position of the diodes). A B C Circuit 3

answer A B C Circuit 3 A & C only

LDRs and Thermistors

While carrying out the experiment: LDR investigation You will carry out an investigation to measure the resistance of an LDR at different light intensities. An LDR is an electric component whose resistance varies with light intensity. Method: Connect the LDR to a multimeter and set it to 20kΩ, Place a desk lamp so that the bulb is 10cm away from the LDR and record the resistance Vary the desk lamp distance and measure the resistance accordingly. Light intensity can be expressed as an ordered variable: bright, medium and dim. Plot a graph of resistance against light intensity. While carrying out the experiment: Explain how you are keeping your test fair Explain how you are making your readings accurate Draw a diagram of the experiment

Thermistor investigation You will carry out an investigation to measure the resistance of a thermistor at different temperatures. A thermistor is an electric component whose resistance varies with temperature. Method: Heat 250ml of water using a bunsen burner to 80ºC then turn the bunsen burner off, Immerse the thermistor in the hot water, Connect the thermistor to a multimeter and set it to 20kΩ, Record the temperature of the water as it cools down Record the resistance of the thermistor for each corresponding temperature Plot a graph of resistance against temperature. While carrying out the experiment: Explain how you are keeping your test fair Explain how you are making your readings accurate Draw a diagram of the experiment

Thermistor high temperature Resistance Current (A) low temperature temperature Voltage (V) Thermistor – resistance DECREASES when temperature INCREASES LDR light Resistance Current (A) dark Light intensity Voltage (V) Light dependant resistor – resistance DECREASES when light intensity INCREASES

Thermistors and LDRs can work as Sensors: A sensor is a component that allows a physical quantity to change its resistance and hence control the amount of current flowing in a circuit. A A Light Dependent Resistor/ LDR: Its resistance decreases as the light intensity increases. (The higher the illumination, the higher the current Temperature Dependent Resistor /Thermistor: Its resistance decreases as the temperature increases. (The higher the temperature, the higher the current). In this circuit, the LDR can work as a lightmeter. The higher the ammeter reading, the higher the illumination. In this circuit, the thermistor can work as a thermometer. The higher the ammeter reading, the higher the temperature.