# Resistance

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## Resistance

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1. Resistance

2. Challenge Try and increase the temperature of 200 ml of tap water as much as possible in five minutes using the equipment provided.

3. Looking down into an electric jug

4. Some examples of incandescent lights • For each part of the household light globe labelled in the diagram explain what its function is.

5. Explain the role resistance plays in … • conductors • insulators

6. In your prac report use the following questions to help discuss your results. • Come up with some reasons to explain why thin wire is wrapped in coils around the ceramic support, and why the element heats the water so quickly. • Why do you think the jug’s body is ceramic and not metallic?

7. Activity • pHET Activity Handout • http://phet.colorado.edu/en/simulation/resistance-in-a-wire • Also on wiki

8. Resistance • Resistance of an electronic component refers to how difficult it is for electrons to flow through it. • The unit of resistance is the: ohm.

9. Resistance • Components can have widely differing resistance values • Eg. metal wires – no (or very little) resistance • Light globe – resistance of 40 ohms • Volt meter – resistance of 5 million ohms • There are two main types of resistors: • Fixed resistors • Variable resistors

10. Fixed Resistors (ohmic conductors) • Made from a solidified carbon mixture • Very useful in electronic circuits because they maintain their set resistance value • Deliberately placed to ‘use up’ a given amount of voltage in a circuit, reducing the voltage available to other components in the circuit • Coloured bands are used to indicate the value of its resistance • Because the resistor is so small the 1st three bands represent the resistors value, the 4th band is used to indicate the accuracy of the stated resistance value

11. Resistor Bands