- Resistance
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Objectives:
- To be able to explain what affects resistance in a circuit
- To be able to use the equation V=IR
- To be able to draw current-voltage graphs
Timing: 2-3 lessons
Now you will look at how wiring is used to transfer the electricity to the devices that need it. Obviously when you have a power cut at home, it's a bit of an inconvenience but just think of what would happen if a hospital had a power cut. How do you think they overcome this?
Find out the circuit symbols for the following: resistor, variable resistor, bulb, cell, battery, switch and power supply.
Explain what happens in a circuit when it is switched on, in terms of charges. What happens when there's a break in the circuit and why?
Explain what a resistor is and what it does. Find out the equation relating resistance, voltage and current. What are the units for each of these things? Also find out what a variable resistor or rheostat does and give an example of where one might be used. How does it work?
You could carry out an investigation looking at the relationship between length of a wire and it's resistance.
Your teacher will probably get you to carry out some experiments looking at the effect of putting resistors and variable resistors into a circuit, although the variable resistors in the circuit kits are a bit pants!
Your teacher may also get you to carry out an investigation to look at the relationship between current, resistance, voltage and temperature in various circuits containing a bulb or an ohmic conductor. You can plot voltage-current graphs and calculate the resistance. Explain the shape of the graphs in terms of what's happening to the resistance. The following sheets may help: "Current-voltage graph for a metallic conductor", "Current-voltage graph for the filament of a light bulb" or "Investigating Resistance".
Have a go at the resistance activity at: http://target.raf.mod.uk/students/Science/Kitchen/Physics/.
You could do the following worksheets:
