AQA A Physics Unit 4 24th Jan 2012

Anyone got questions for the last two chapters? (Besides the ones in the book)

Have you done the old spec papers, I remember they're being quite a few for the last two chapters?

Aren't they only multiple choice ones and calculation ones on the old spec papers? Haven't looked at them in properly yet though.

If there was a 6mark question on gravitational and electric fields, what do think it would be about.

Link please, I can't find it

Need help with this question - a current of 8A is passed through a conductor of length 0.4m and cross-sec. area of 1x10-6m^2. The conductor contains 8x10^28 free electrons per m^3. When the conductor is at right angles to a magnetic field of flux density 0.2T, it experiences a magnetic force. What is the average magnetic force acting on one of the free electrons?

Need help with this question - a current of 8A is passed through a conductor of length 0.4m and cross-sec. area of 1x10-6m^2. The conductor contains 8x10^28 free electrons per m^3. When the conductor is at right angles to a magnetic field of flux density 0.2T, it experiences a magnetic force. What is the average magnetic force acting on one of the free electrons?

I've tried to work it out, but I'm not sure if I've done it correctly. Do you have a mark scheme?

i need help on question 2 january 10 section a please thank you.

Has anyone got any transformer questions from the old spec.

It's pretty difficult isn't it, I need help on that as well.

If it's this one:
Water of density 1000kgm^(-3) flows out of a garden hose of cross-sectional area 7.2*10^(-4)m^(2) at a rate of 2.0*10^(-4)m^(3) per second. How much momentum is carried by the water leaving the hose per second?

Then I was looking for this too and found it on TSR.

As it's asking for momentum, we can use the equation p=mv, we want to find p, so we must work out m and v.

To find m, we do density*volume, so 1000kgm^(-3)*2.0*10^(-4)m^(3) which gives us 0.2kg because the m^(-3) and m^(3) when multiplied cancel out.

Then to find v, we do volume/area, so 2.0*10^(-4)m^(3)s^(-1) / 7.2*10^(-4)m^(2) which gives us 5/18ms^(-1) because m^(3)/m^(2) = m.

Multiply m and v, so (5/18)*0.2= (1/18) which can be written as 5.6*10^(-2) and the units we get are kgms^(-1) which can be written as Ns.

So we find the answer is B which the mark scheme agrees with.

can someone explain to me how you get these 2 equations as i have seen them as solutions on past papers

0.5mv^2=GMm/r and delta V = GM(1/R - 1/r)

thanks

Also I was wondering - can anyone enlighten me on question 14?

http://store.aqa.org.uk/qual/gce/pdf/AQA-PHYA4-1-W-QP-JUN10.PDF

Don't understand why the answer is (a) as I put (b)...