You are Here: Home >< Physics

Electristity question Watch

1. I don't really get 7b part 3 where you have to find out the emf of the battery supply could anyone help me out.

The answers for the rest are follows:

Resistance= 0.98 ohms

Current= 2.08 A

Voltage= 2.04 V

Could anyone please help me find the emf, none the equations I try actually work?? The question is in the attachment!

Posted from TSR Mobile
Attached Images

2. ANYONE!!!

Posted from TSR Mobile
3. Well, P = IV, So the EMF = Power (in watts) / Current (in amperes)

Edit: Not quite sure what you're asking for?

The EMF (in Volts) = P/I = 4.25/2.08 = 2.04 as you originally stated
4. What equations are you using that don't work?

V = E - Ir

V = pd across the external circuit (V)
E = emf of the cell (V)
I = current through the cell (A)
r = value of the internal resistance (&Omega; )
(Ir = the p.d. across the internal resistor)

V = E - Ir
2.04 = E - (Ir)
2.04 = E - (2.08x0.98)
2.04 = E - 2.0834
E = 2.04 + 2.0834
E = 4.1234

I have no idea if that's right... I managed to grab an A in Physics but that was over 7 years ago haha!
5. Look at the second. Photo attachment thats the question! The answer in the mark scheme is 16.1 V

Posted from TSR Mobile
6. Well I got 4.1234v.... Just multiply my answer by 4 and you've got 16.4v which is close enough!

I'm sure someone who can actually help you will be here soon!
7. (Original post by Rybee)
Well I got 4.1234v.... Just multiply my answer by 4 and you've got 16.4v which is close enough!

I'm sure someone who can actually help you will be here soon!
Its a pretty weird question as you cant use any of the emf equations really need help on this

Posted from TSR Mobile
8. Anyone!!!

Posted from TSR Mobile
9. Someone!!!

Posted from TSR Mobile
10. There are two wires going around the circuit, this surely means they are parallel wires? Does that help?
11. (Original post by raiden95)
There are two wires going around the circuit, this surely means they are parallel wires? Does that help?
So how do you find the emf?

The equation for emf is E = V + Ir and you don't have internal resistance

Posted from TSR Mobile
12. (Original post by Jimmy20002012)
So how do you find the emf?

The equation for emf is E = V + Ir and you don't have internal resistance

Posted from TSR Mobile
Maybe there is no internal resistance? Do you have resistance in each wire? Do you have overall current?
Work out total resistance in parallel, then use E=IR

I'm not 100% sure this is correct, but after i left the exam in january I wish i did this.

EDIT: sorry about the mistake, the internal resistance is in the copper wire i believe, and the total internal resistance 1/r = 1/0.98 + 1/0.98 is it not?

Let me know how you do, that's how I think its done my answer is 3.06V or 13.0V, do you know the answer?
13. (Original post by raiden95)
Maybe there is no internal resistance? Do you have resistance in each wire? Do you have overall current?
Work out total resistance in parallel, then use E=IR

I'm not 100% sure this is correct, but after i left the exam in january I wish i did this.

EDIT: sorry about the mistake, the internal resistance is in the copper wire i believe, and the total internal resistance 1/r = 1/0.98 + 1/0.98 is it not?

Let me know how you do, that's how I think its done my answer is 3.06V or 13.0V, do you know the answer?
The answer is 16.1v and the solution is that they do:

12 + 2 x 2.04 = 16.1 V

No idea what you do

Posted from TSR Mobile
14. The lamp is working at rated capacity so you've got 12v across the bulb and 2.04v across each of the two wires connecting it to the power supply.
Seems straightforward tbh.
15. (Original post by Jimmy20002012)
The answer is 16.1v and the solution is that they do:

12 + 2 x 2.04 = 16.1 V

No idea what you do

Posted from TSR Mobile
Haha thats weird, i said 3.06 or 13.0 add them its 16.06 which is 16.1 1dp
16. (Original post by raiden95)
Haha thats weird, i said 3.06 or 13.0 add them its 16.06 which is 16.1 1dp
There is 12V across the source, as stated in the question. Then, visualise the circuit, paying particular attention to the way that the wires are organised (parallel/series). Then use the appropriate circuit rules to work out the total emf, which is the solution as given. I did this paper in January and got above 90%.
17. (Original post by American Vampire)
There is 12V across the source, as stated in the question. Then, visualise the circuit, paying particular attention to the way that the wires are organised (parallel/series). Then use the appropriate circuit rules to work out the total emf, which is the solution as given. I did this paper in January and got above 90%.
Haha same! I got 94% but if i got this question right would have been better!
18. 90% and 94% that is amazing, what tips could you give me in order to get that? I got 55/70 which was 1 mark of an A which was annoying, I found out I got full marks in the quantum and particles bit and totally messed up in the electristy bit

Posted from TSR Mobile
19. (Original post by Jimmy20002012)
90% and 94% that is amazing, what tips could you give me in order to get that? I got 55/70 which was 1 mark of an A which was annoying, I found out I got full marks in the quantum and particles bit and totally messed up in the electristy bit

Posted from TSR Mobile
Same really, had full marks up till Q4, lost 2 marks on the question above, other 4 here and there worded questions. Tips would be just make sure you really understand everything going on in a circuit, I myself didn't completely know which is why i lost marks
20. Would you mind attaching the mark scheme here?

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: April 4, 2013
Today on TSR

What is the latest you've left an assignment

And actually passed?

Simply having a wonderful Christmas time...

Discussions on TSR

• Latest
• See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• Poll
Discussions on TSR

• Latest
• See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.