# Help with Electricity interview lesson

Discussion in 'Science' started by ryanstobie, Jan 19, 2011.

1. ### ryanstobie

Hi guys
I have an interview lesson on Friday to a high level AS group on pd and emf.
I need to; define pd, the volt and how voltmeters work, define emf and explain the difference between emf and pd and finally use the equation W = VQ.
Basically I need to make the lesson interesting some how, any ideas?
Thanks
<table><tr><td>Hi guys
I have an interview lesson on Friday to a high level AS group on emf and pd.
I need to; define pd, the volt and how voltmeters are used, define emf and the difference to pd and use the equation W=VQ
Basically I need to make the lesson interesting some how, any ideas?
Thanks
</td></tr></table><table><tr><td>Hi guys
I have an interview lesson on Friday to a high level AS group on emf and pd.
I need to; define pd, the volt and how voltmeters are used, define emf and the difference to pd and use the equation W=VQ
Basically I need to make the lesson interesting some how, any ideas?
Thanks
</td></tr></table><table><tr><td>Hi guys
I have an interview lesson on Friday to a high level AS group on emf and pd.
I need to; define pd, the volt and how voltmeters are used, define emf and the difference to pd and use the equation W=VQ
Basically I need to make the lesson interesting some how, any ideas?
Thanks
</td></tr></table>

2. ### physics_suits_you

Being an old dinosaur, I always equate "guys" with "men" - hopefully I am wrong!
Also, how did you get it to repeat 4 times? I would be wary of appointing anyone who says everything more than once and doesn't check their work.
Additionally, I would ask "what ideas have you already got"? I wouldn't want to appoint someone whose sole technique was to take ideas from others. So, if you give me a few of your thoughts, I'll happily share a few of mine.

3. ### ryanstobie

Guys is meant as a generic term for everyone, maybe a South African thing.

Not sure about the four times thing, I've never used the TES community before, I tried to paste what I had typed in word but it didn't seem to let me...although clearly it did.

Still reading up on the topic, finished my Physics degree a while ago and only started teaching it to Key Stage 4 in September, still finding me feet. I thought perhaps of showing the emf of a lemon as a starter to get across the idea of emf being another type of energy being converted to electrical energy, though I'd probably need a DMM to read it. It would also tie in nicely with anodes and cathodes which were touched on in the previous section.

Thinking about it now I could get the class to connect the lemons in series later and calculate the emf, then measure it using a volt meter, when the numbers are different I can explain the difference between the two and discuss where the missing emf went.

What do you think?

4. ### physics_suits_you

SORRY - the website wouldn't let me log in yesterday, despite trying between 10am and 11pm on numerous occasions.
Presumably by now you are doing your interview, so any help would be wasted. However, for the record:
I did fruit batteries in KS3, so would not see them as appropriate for a bright AS group, although there may be a degree of stimulation there.
Your use of phrasing "emf being another type of energy being converted to electrical energy" is a little odd, but I know what you mean and you were probably in a hurry.
Most schools probably use DMMs regularly, but for a demo a large analogue meter is always good, although you may have a projection system to get visible effects from a digital meter.
If you can access a variety of voltmeters, especially old analogue ones, you can connect then individually to a battery & lamp: with luck you get significantly different readings. When you connect more than one, the "low" reading is always the one they agree on - the real voltmeter is not ideal (infinite resistance) and so actually affects the circuit (parallel resistance). EMF is what you get when there is no current drawn! (Slightly different aspect but achievable)
Ask students how the volt is obtained and they will tell you V=IxR. Ask how R is obtained - circular argument. As I'm sure you appreciate, I is a basic quantity (worth quoting - infinitely long wire in a vacuum etc - I always ask them to consider the force in comparison to the weight of a fly) and V is derived from energy considerations (from M,L,T - all basic). Perhaps I might use an electric motor to lift a weight (ignore efficiency). Confirm that changing the voltage (& I) alters the rate of energy conversion.
Give students a short practical to confirm that V = V1 + V2 using high value resistances in series. Do the results agree exactly or is there an error to be accounted for (important on AS course)? Repeat with low resistance values - is the output voltage always the same? Repeat with resistors in parallel - with low value resistors, the current drawn will drop the output voltage because of the internal resistance of the cell (try not to use power packs, although you can get an effect). You are then introducing a new idea to be dealt with next lesson / challenging bright students. Ask what they learnt for KS3/KS4 when lamps were connected in parallel (have some to demo).
Please let us know how you got on.