2011 GCE O Level Pure Physics P2 Suggested Solutions (Finally Released)

JamesKhoo

Erm, so at the end of the day, when do we use right hand rule and when do we use left hand rule? If the answer is that to find force, we use left hand right, to find current, use right hand rule, then lets say the 1st scenario is that the magnetic field is pointing towards the screen, the current is to the right, using left hand rule, the force will be upwords. 2nd scenario is that the magnetic field is still pointing towards the screen, the force still pointing upwords, but the current is in an opposite direction? Thanks btw, its for general knowledge and future physics questions and not anything else (:

JamesKhoo

冷风1985 发表于 4-11-2011 16:15
Your answer could be wrong. That is not the reason. That is the difference of their properties.
Wh ...

erm teacher, one of the 7 properties to an emf wave is that its transverse so perhaps that is applicable..?

无奈的我啊

Right hand rule to find direction of induced current in A.C. motor,
The current is induced due to the rotation by the hand, producing change in magnetic flux linkage.
Since Qn asking for force, ts obviously asking for left-hand.
The induced current produces a magnetic field. The interaction of this magnetic field and the magnet's own, causes a downwards resultant force as determined by Fleming's LHR

JamesKhoo

okay i get your part, left hand rule to find force while right hand rule to find induced current. But if the scenario is exactly the same but the result they want you to find is different.
So lets say the first situation tells you that magnetic field points towards the screen and the current is to your right. so since to find force, using your method of left hand rule for this case, force is upwords.
but then the second situation tells you the force is upwords and magnetic field is towards the screen, so using your method, we use right hand rule, and current is to the left.
for the exact same situation we have 2 different possibilities, how can it be?

你猜

请问Question 4,part (c)的period到底是2.0s还是4.0s?

冷风1985

JamesKhoo 发表于 5-11-2011 20:31
okay i get your part, left hand rule to find force while right hand rule to find induced current. Bu ...

JamesKhoo, what has confused you is that you didn't differentiate "Direction of Force" and "Direction of Motion".
Using LHR, to determine, the result is "direction of force".
Using RHR, what is used is "direction of motion".

That is to say, when the coil is moving up it experiences a force in the opposite direction.

冷风1985

你猜 发表于 6-11-2011 00:03
请问Question 4,part (c)的period到底是2.0s还是4.0s?

should be 2.0s.
Many students have this of misunderstanding:
     in one period, a particle passes through a particular point two times  (1)
so, when particles return to the same position, it takes 1/2 period.         (2)

In the above statment (1) => (2)
(1) is correct, but (1) cannot imply (2) although it seems so.

Explaination:
(2) is only correct for points located at the equilibrium position. other than those places, the particles take either longer or shorter time than 1/2 period to return to the same position.
    For example: particles at the peak or trough will take exact 1 period to return to the same position.

Hope this clears your doubts.

冷风1985

无奈的我啊 发表于 3-11-2011 22:25
即使是 all the particles，但是他们都会在一个Period间，有两次的回到原点？

           

请看56楼.

烈帝～

:'(:'(考物理那天不在状态:'(:'(很多怪怪的低级错误都出来了。。。。郁闷死了～

你猜

冷风1985 发表于 6-11-2011 10:14
should be 2.0s.
Many students have this of misunderstanding:
     in one period, a particle pass ...

Thank you very much.