EE Qs: Torn Between C & D - Can Anyone Explain?

[Flatshoe]

I'm torn between C and D, can anyone explain which answer is which and WHY?

Also, I don't know whether the answer to this is "in" or "out", however I'm quite sure it's out. Does the direction of a magnetic field have to be North to South?

 

[Zryn]

For the first one, keep in mind that a sin wave is written as A*sin(w*t). For a given frequency, what is w (omega)?

For the second one, are you familiar with "the right hand rule"? Making a gun with your thumb and index finger and then orienting your middle finger at a right angle to your index finger.

Thumb = Force
Index = Field (Magnetic)
Middle = Current

So the field/index goes down (from north to south), the current/middle goes from left to right, the force should be your thumbs direction.

 

[karthicknar]

for the first question, you should keep in mind that in EE we always write as below v(t)=2*sin(2*pi*f1*t)+2*sin(2*pi*f2*t)+4sin(2*pi*f3*t)

Match this with the given equations and find f1, f2 and f3.

for second question, you have to use Fleming's left hand rule. The figure represents motor action. Keep middle finger in direction of current, index finger in direction of flux from north to south pole, now your thumb shows direction of force acting on the conductor.