1. oisture Tester The Circuit &Components

2. Objectives Understand the purpose of Resistors Understand Resistor Colour Code Understand how a Transistor works Understand our Circuit

3. So what is a Circuit?… It is a bit like a race track - the track must be complete for the car to get round, otherwise, it cant go any further. A circuit is something that electricity flows around. It is the same for electricity. If the circuit is broken, the electricity cannot get around the track and nothing will happen, ie, the light wont come on.

4. Resistors… Resistors are used to control the flow of electricity around a circuit. Resistors are measured in Ohms (Ω), and there are lots of different values.

5. What do you think would happen if there were no resistors in your circuit?

6. You know that you can write: 1000 ml = 1 Litre Well, you can shorten the value of resistors too: 1000 Ohms = 1K Ω Other values can also be shortened: Examples: 1800 Ω = 1.8 KΩ or 1K8 49K Ω = 4.9K Ω or 49000 Ω

7. Transistors… …An un-pressed switch If there is no voltage (or power) running through the base, it acts like an insulator and does not allow electricity to flow through. This means the light in your circuit will not come on. … A pressed switch When a voltage is applied to the base of the transistor, it becomes a conductor, and does allow electricity to flow through. This means your plant does not need water so the light will come on.

8. LED (light) Transistor Battery Moisture Probes Battery Moisture Probes PLANT IS OK Here, the light is switched on. There is moisture making a connection between the probes, so the transistor is an conductor, switching the light on. PLANT NEEDS WATER Here, the light is switched off. There is NO moisture making a connection between the probes, so there is no current running into the transistor (it is an insulator here).

9. Resistor Colour Wheel Take a resistor colour wheel sheet. Colour this as it says, and then cut out each wheel. Assemble the wheel with a pin and put it onto the bottom of your sheet.

10. Plenary What was positive about the lesson? What was negative about the lesson? What was interesting about the lesson? Can you describe how our circuit works? What does a transistor do? What does a resistor do? What is the value of a brown black green resistor?