Physics internal resistance problems

Hi i can't find the mark scheme for these questions anywhere and have no idea whether or not I have answered them correctly so could anyone experienced in the physics field let me know if they are correct? Thanks



Btw I know part (iv) is wrong so any help will be appreciated


Posted from TSR Mobile

Hi i can't find the mark scheme for these questions anywhere and have no idea whether or not I have answered them correctly so could anyone experienced in the physics field let me know if they are correct? Thanks



Btw I know part (iv) is wrong so any help will be appreciated


Posted from TSR Mobile

Part (iv)

First, find the total resistance in the circuit using the EMF and current:
V = IR
V / I = R
R = 15/(10x10^-3)
R = 1500 Ohms

Now, you can form an equation with the unknown resistance:
(1/1200 + 1/X)^-1 + 540 = 1500

Rearrange it:
(1/1200 + 1/X)^-1= 960

Get rid of the power of -1 on the left:
(1/1200 + 1/X)= 1/960

Rearrange now to get the unknown on its own:
1/X = 1/960 - 1/1200
1/X = 1/4800

To get from 1/X to X just times by the power of -1:
(1/X)^-1 = (1/4800)^-1
X = 4800

So the thermistor has a resistance of 4800 Ohms, to check just substitute this value into the original resistance calculation and you should get 1500 Ohms.

My method is a little confusing, but I hope it helps

Thanks for your reply.

It's worth remembering that the best learning is when the student reaches the answer for themselves which is why it's best to guide rather than give out full solutions which can then be copied verbatim.

We had a saying at uni' when some lecturers wrote solutions onto the whiteboard: it's the most efficient method for getting what is in the lecturers handwriting into our own handwriting without anything passing through either brain!