Isaac Physics C4a HELP

How do I do any of the Isaac Physics questions I have to hand it in by tomorrow but it is so hard, I have been given hints last weekend but they helped me little to none. Please help on C4a. It would be much appreciated.

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Reply 1

Callicious

Could you post the question? Ideally in text form with any accompanying images? (or just an image...?)

Reply 2

Fleeb

The url: https://isaacphysics.org/questions/phys19_c4a_q4?stage=all

I couldn’t download the image.
The three questions are find the equivalent resistance in the circuit in terms of R.
Find the potential across R1 in terms of V and do the same for R2.

Reply 3

Callicious

Original post by Fleeb

The url: https://isaacphysics.org/questions/phys19_c4a_q4?stage=all

I couldn’t download the image.
The three questions are find the equivalent resistance in the circuit in terms of R.
Find the potential across R1 in terms of V and do the same for R2.

You can use the snipping tool on Windows (they give it to you as an SVG which is why you had trouble downloading it- converting an SVG to PNG/JPEG is readily doable though.)

Try to redraw the circuit a bit-

Does this make it better?
Edit: If you don't tag someone when you reply, they won't know you did- I didn't reply fast to this post because I wasn't tagged in your reply, sorry! :-;

(edited 2 years ago)

Reply 4

Fleeb

Original post by Callicious

Does this make it better?
Edit: If you don't tag someone when you reply, they won't know you did- I didn't reply fast to this post because I wasn't tagged in your reply, sorry! :-;

Hi there, sorry for not responding sooner, do u know which ones are R1, R2?
Thanks again for the help. There are also 9 resistors?

(edited 2 years ago)

Reply 5

Callicious

Original post by Fleeb

Hi there, sorry for not responding sooner, do u know which ones are R1, R2?
Thanks again for the help. There are also 9 resistors?

Sorry forgot to add the last one; in any case the diagram should help a bit

Reply 6

Jail_break

Original post by Callicious

Sorry forgot to add the last one; in any case the diagram should help a bit

I used Kirchhoff's voltage law for the diagram to find the equivalent resistor but got 17/7 R, which is incorrect? Does anyone know where I've went wrong please?

Reply 7

mqb2766

Original post by Jail_break

I used Kirchhoff's voltage law for the diagram to find the equivalent resistor but got 17/7 R, which is incorrect? Does anyone know where I've went wrong please?

You're close. Upload what you tried?

Reply 8

Jail_break

Ohhh I get it- I didn't write out my working out the first time and got 17/7, instead of 18/7. Thank you for helping me realise my silly mistake :s-smilie:

. Anyways, I've attached my working out at the bottom.

Screenshot 2021-12-25 8.56.56 PM.jpg46.5KB

Reply 9

mqb2766

Original post by Jail_break

Ohhh I get it- I didn't write out my working out the first time and got 17/7, instead of 18/7. Thank you for helping me realise my silly mistake :s-smilie:

. Anyways, I've attached my working out at the bottom.

Didnt do anything :-), but good youre sorted.

Reply 10

Jail_break

Original post by mqb2766

Didnt do anything :-), but good youre sorted.

Came back to the question and I'm absolutely baffled with parts B and C - how are you meant to calculate the p.d across the resistors?

Reply 11

mqb2766

Original post by Jail_break

Came back to the question and I'm absolutely baffled with parts B and C - how are you meant to calculate the p.d across the resistors?

B is relatively straightforward. You have two Rs and a "total resistance" in series. Whats the pd across the "total resistance", how does this relate to the pd across R1?

Reply 12

Jail_break

Original post by mqb2766

B is relatively straightforward. You have two Rs and a "total resistance" in series. Whats the pd across the "total resistance", how does this relate to the pd across R1?

To find the P.D across the total resistance, don't we need the current of the 18/7 ohm resistance? How do we find that? And do we consider the loop with R, R_1 and R?

Reply 13

mqb2766

Original post by Jail_break

To find the P.D across the total resistance, don't we need the current of the 18/7 ohm resistance? How do we find that? And do we consider the loop with R, R_1 and R?