# AS level Physics Resistances Electricity Question Help

Hi,
I'm kinda lost on this part of a muti sub part questions.
I don't want to assume that 12V is across the 25 ohm resistor and then use the V=IR formula.

the questions mentions that the max resistance is 25 ohms and the minimum reading on the voltmeter is 0.75 v

(edited 1 year ago)
What are you trying to find?
Original post by Kitty_Kat31415
What are you trying to find?

The resistance.
I didnt mention before but P can slide and is mounted on a copper bar.Component P can slide between X and Y.
And the 0.75v reading is when is P moved and is the lowest value.
Original post by ANeRd
The resistance.
I didnt mention before but P can slide and is mounted on a copper bar.Component P can slide between X and Y.
And the 0.75v reading is when is P moved and is the lowest value.

You need to find the current in the circuit using V=IR

12 = I x 25

I = 12/25 A

Sub this into V=IR for the lamp

0.75 = 12/25 x R

R = 1.6 ohms
Original post by akshayjjjj
You need to find the current in the circuit using V=IR

12 = I x 25

I = 12/25 A

Sub this into V=IR for the lamp

0.75 = 12/25 x R

R = 1.6 ohms

Thanks for the reply,really appreciate it

I initially did this and only got 1 mark out of 2 or 3.
I read the examiners read report for the questions and it states "Student assumed that the 12 V was across the 25 Ohm resistor".
Original post by akshayjjjj
You need to find the current in the circuit using V=IR
12 = I x 25
I = 12/25 A
Sub this into V=IR for the lamp
0.75 = 12/25 x R
R = 1.6 ohms

why aren't we taking the resistance of the lamp into account when doing 12 = I x 25 ?
Q8 https://filestore.aqa.org.uk/sample-papers-and-mark-schemes/2022/june/AQA-74071-QP-JUN22.PDF
MS says you should do V=12-0.75 to get R as 1.7 so I think youre right