Revision as of 12:16, 9 February 2010

Outcomes

• Pupils can use E = IVt
• Pupils can talk about the difference between a.c. and d.c.

Specification References

• 2.7 use the relationship between energy transfered, current, voltage and time:

E = IVt

• 2.8 recall that mains electricity is alternating current (a.c.) and understand the difference between this and the direct current (d.c.) supplied by a cell or battery

Starter

Using the PASCO light sensor (as introduced in ELEC-4) measure the light given off by a torch and by a lamp. The first time you do this you should set the sample rate to a low value (e.g. 10Hz or 25Hz, talk about frame rate if you like). You should get two flat lines (at different light intensities).

Next crank up the sample rate to the MAX (1000Hz) and repeat. You'll get lots of data points so you only need to run it for 0.2s max. Expand the scales and you should see the torch is still a (reasonably) flat line whilst the lamp varies with a cycle frequency of 100Hz (this is due to the negative part of the a.c. signal still producing the same light, i.e. the frequency of the mains is doubled)

If you are unsure about using PASCO graphs or adjusting sample rates then speak to PAS for a quick run down.

Main Body of Lesson

Make some notes about a.c. and d.c. - nothing too complex, they just need to be able to comment on the difference (either from their own knowledge or referring to a graph)

Plenary

Homework

Additional Information

Resources Required

• PASCO light sensor (+ hub etc.)
• mains lamp
• torch (cell powered, not flamming)
• electricity meter (retro)
• electricity meter (modern)
• a selection of mains appliances (do we have anything more powerful than a kettle?)

Textbook References

Website References

Skills Addressed

Safety/Hazards

Notes