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# Unit 4 (AQA) Help

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1. Hey guys I needed some help with some questions on the January 2010 Paper.
https://60abffc9b401b1c0936e01291c15...%20Physics.pdf

With 25, I just don't know how to work my way through the question, I seem to be getting random answers.

With question 22, I do not understand why the answer is C. I thought the answer is B because I read that we would have to treat an electron moving north as a positive charge moving south? Or has this got something to do with sin(θ) ?
2. Hi, I'll try to help.

25 - Okay so emf is the rate of change of flux (linkage) which is Emf = BAN / t. Well N=1 since there are no coils/turns. So what's B, A and t? Well B = 1x10-5 . Now the hard part is A and t. The velocity of the plane multiplied with the wingspan gives us an area which is created per second. Thus Length x velocity = A/t right? So our emf is our area per second created by the plane multplied by the flux density. Shown here:

since lv = A / t then Blv = BA / t.
Our emf = BAN / t, but N = 1 so emf = BA / t

Therefore E = Blv. So plugging the numbers in we get 0.09V. (A)

22- This is because the electron is moving parralel to the magnetic field lines. A charged particle does not feel a force from a magnetic field unless it is at and angle to the field lines all the way to perpindicular to the field lines. It has got do with sinθ. When it is parralel then θ = 0 so sin90 = 0. So it experiences no force and thus itsn't accelerated. So it will continue moving in the same direction with the same speed.
3. (Original post by SirRaza97)
Hi, I'll try to help.

25 - Okay so emf is the rate of change of flux (linkage) which is Emf = BAN / t. Well N=1 since there are no coils/turns. So what's B, A and t? Well B = 1x10-5 . Now the hard part is A and t. The velocity of the plane multiplied with the wingspan gives us an area which is created per second. Thus Length x velocity = A/t right? So our emf is our area per second created by the plane multplied by the flux density. Shown here:

since lv = A / t then Blv = BA / t.
Our emf = BAN / t, but N = 1 so emf = BA / t

Therefore E = Blv. So plugging the numbers in we get 0.09V. (A)

22- This is because the electron is moving parralel to the magnetic field lines. A charged particle does not feel a force from a magnetic field unless it is at and angle to the field lines all the way to perpindicular to the field lines. It has got do with sinθ. When it is parralel then θ = 0 so sin90 = 0. So it experiences no force and thus itsn't accelerated. So it will continue moving in the same direction with the same speed.
Thank you so much!

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