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[giga502]

Hi Guys,

I've had a physics worksheet to do and there's been various questions that I couldn't answer so I was wondering if you guys out there could help me. I've got the answers as they are supplied but I'm just not sure on how they work and some of the formulas that comes with them. Hope you guys can explain it to me thanks. Ok here we go;

8. A cell of 2V and negligible resistance is connected to two resistors in series. The current through the cell is 0.2A. If one resistor consists of two resistance coils of 5Ohms and 10Ohms respectively arranged in parallel. Find the;

a) the other resistance.

Well I figured out this question. We use R=V/I, 2/0.2 = 10Ohms
Then we figuredout the total resistance in the parallel circuit and it worked out to be 10/3Ohmd. So we subtracted 10-(10/3) and we have the resistance of the resistor in the serious circuit not the parallel one.

b) The potential difference across the 5Ohm coil. <<<<<Didn;t understand.


9. A resistor of 10Ohms is connected in series with two other resistors. (6 ohms and 30ohms) that are in parallel, If a current of 3A flows from the battery find.

a) the total resistance

1/Rt=1/30+5/30=6/30=30/6=5.Ohms Since in series we just add to find the total resistance 5+10= 15 Ohms


b) the emf of the battery (could somone explain what emf is?)

3x15=45V <<<<<<wasn't quite sure how i did it I just guesses

c) the current through each resistor <<<didn't get this one


10. The resisivity of constantan is 4.9x10&-7Ohm Metres<(idono). What resistance of a long piece of constantan wire 1m long and a radius of 0.1mm.

Completley lost here.


13. A 100W, 250V lamp is used on a 200V supply.

a) What will be the current flowing through the lamp <<<didn't get


b) Explain why it is more economical to use a lamp labeled 250V but it is used on 200V mains. <<<also didn't get


Hopeu can help guys thanks =]

[SF]

No homework help.