Higher Physics

For qu. 23b in 2007, I don't understand how you work out the amount of helium that can't be let out of the cylinder (can't be used)

Yeh I understand why the helium can't escape from the cylinder, because it is simply being "let out" and will stop when the pressure inside the cylinder = air pressure, but i'm not sure how you can calculate how much helium is actually left in the cylinder.

Would someone mind explaining 2005 Q14?

It's just the volume of the cylinder i.e. the 8*10^-2 mentioned at the start of the question.

For 25b(ii), you need to work out the pd across the 220 ohm resistor. This is voltage XY across the capacitor, not the supply voltage

It's just one of those things you're expected to know. When a wave passes into a different medium (i.e. from air into oil) the frequency of the wave remains constant (but the velocity and wavelength change!)

One thing I can't find in my notes is how changing the frequency affects a capacitor. I know frequency has no effect on a resistor, and that it does on a capacitor - I just don't know exactly what.

but why for 16 do they remain the same? Is it due to the refractive index being the same?

An increase in frequency results in an increase in the current in a capacitive circuit.

I'm not too worried (yet) about Physics. Still need to finish off some older past papers and read my notes on pn junctions and especially MOSFETs!

I can't seem to get the SQA answer for 25. (C) 2005 Past Paper. They state it is 0.4A. I disagree.

My working:

1/R(total)= 1/15 + 1/30 = 1/10 .. R = 10 ohms

V= 6 V

V=IR .. 6 = I x 10 .. I= 6/10=0.6A

..Hrmm.. could someone tell me the stupid mistake I'm making? :P

MOSFETs are so crap, but luckily you only really need to know a little and just learn it, not understand it. The only past paper question I have seen was one labelling gate, drain and source - I thought it was easy but got it wrong I put it with source on the top, but its drain on the top.

Ok cheers about the frequency, so is it a curve like this:



All I am concerned about now is some parts of electricity, and PS questions on unit 3. In electricity I sometimes get really confused working the pd across bits etc. - and Unit 3 just isn't my strong point.

Another question, I know that for a balanced wheatstone bridge r1/r2=r3/r4 - when it is out of balance how can you work out the PD across it (in the middle bit)?

Ok cheers about the frequency, so is it a curve like this:



All I am concerned about now is some parts of electricity, and PS questions on unit 3. In electricity I sometimes get really confused working the pd across bits etc. - and Unit 3 just isn't my strong point.

Another question, I know that for a balanced wheatstone bridge r1/r2=r3/r4 - when it is out of balance how can you work out the PD across it (in the middle bit)?

Is anyone else hoping for:

Drawing vectors/working diplacement from the drawing
A huge d/s/t/a/u/v question.
For unit 3 a nice question involving refractive index, critical angles etc.
An easy op-amp question

^Too good to be true IMO I just hope there isn't anything really bad like a bad problem solving or something too hard.

Anything but that, please =(

I hate those because they are a huge time waste! And I often get the direction mixed up, I hate bearings!