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# AQA-PHYA4-1-QP-JUN14 Question 23

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1. Hello,

How did the mark scheme arrive to this solution?

23) Two electrons, X and Y, travel at right angles to a uniform magnetic field. X experiences a magnetic force, Fx, and Y experiences a magnetic force, Fy.

What is the ratio Fx/Fy if the kinetic energy of X is half that of Y?

Thank you!
2. (Original post by Shmurple)
Hello,

How did the mark scheme arrive to this solution?

23) Two electrons, X and Y, travel at right angles to a uniform magnetic field. X experiences a magnetic force, Fx, and Y experiences a magnetic force, Fy.

What is the ratio Fx/Fy if the kinetic energy of X is half that of Y?

Thank you!
First you find v for both by rearranging the KE equation
so v= square root (2Ek/m)
This is the v for X
Then v for Y, would have 2Ek instead of Ek:
v=square root(4Ek/m)
And so Bqv(x)/Bqv(y) where B and q cancels come to 1/square root 2
The answer is C btw not D
Hope it helps
3. (Original post by Lili1998)
First you find v for both by rearranging the KE equation
so v= square root (2Ek/m)
This is the v for X
Then v for Y, would have 2Ek instead of Ek:
v=square root(4Ek/m)
And so Bqv(x)/Bqv(y) where B and q cancels come to 1/square root 2
The answer is C btw not D
Hope it helps
Thanks for the answer I get it now!
But that's weird the answer really says D.
4. (Original post by Shmurple)
Thanks for the answer I get it now!
But that's weird the answer really says D.
It's June 2015 Q23 not June 2014 maybe that's why
5. (Original post by Lili1998)
It's June 2015 Q23 not June 2014 maybe that's why
Wow thanks a tonne ! I'm shouting like Darth Vader at the moment "nooooo!"

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