Resistance WALT: Describe the relationship between resistance and current and explain how different components can change resistance Starter: Draw the symbol of a variable resistor and explain one use it has

LDR (Light Dependent Resistor) Has low resistance in bright light and high resistance in low light Used in security alarm Draw a sketch of a graph to show the relationship between resistance and light intensity with an LDR

Thermistors Thermistors detect temperature and are designed to decrease the resistance in a circuit as temperature increases They are used in fire alarms Draw a sketch of a graph to show the relationship between temperature and resistance with a thermistor

You have 2 minutes to quickly set up a circuit using a variable resistor, a bulb and an ammeter Adjust the variable resistor and observe the changes in the bulb and ammeter, then sit down

Design an experiment to test the resistance of different lengths of wire Now (before you start), write down: 1. Equipment needed 2. The circuit diagram 3. Prediction 4. Method 5. Results table

When finished: Write a conclusion Investigate an LDR– Set up a circuit to test your theory that LDRs have low resistance in bright light. Use a torch (or light bulbs) and an ammeter. Draw the circuit diagram and explain what you observed. PREP: Draw a graph of your results for length of wire against current

Plenary – Discuss in pairs what you have found out this lesson As resistance increases, current decreases Resistance increases as: Length of wire increases Thickness of wire decreases Different types of wire have different levels of resistance An electric current flows when electrons move through a conductor, such as a metal wire. The moving electrons can collide with the ions in the metal. This makes it more difficult for the current to flow, and causes resistance. The resistance of a long wire is greater than the resistance of a short wire because electrons collide with ions more often. The resistance of a thin wire is greater than the resistance of a thick wire because a thin wire has fewer electrons to carry the current.