4-ELC-05

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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)

Recap P=IV and P=E/t from last year. Discuss alternate units (i.e what is a watt?) aiming for joules per second rather than amp volts. See if pupils can combine the two to give an equation with only P,I,V and t

Set up the old skool electricity meter and demo the spinning disk of energy usage (visable inside the meter at the bottom), add more and more load but be aware of the fuse in the extension lead!

Move onto the new(er) meter which will give V,I,P,E,cost etc. readings. Draw a results table on the board with for the various appliances and note down the data you need (you can use I&V to find P, or use E and t to find P, or both and compare, or use I&V to find P then consider typical use time to find typical energy used). Pupils to use the equations to find stuff out and practice using. Maybe throw in some hours for trixiness.

Some notes for note books.

Plenary

Homework

Homework can either be a slightly modified version of AGRs "How powerful is your house" found in the ELC folder or textbook questions (pg 197 all, 198 7 onwards).

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

84-85

190-191

196-197

Website References

Skills Addressed

Safety/Hazards

Notes