The anwser would be A
hope this helped
Period = 6 seconds and 
.
<u>Explanation:</u>
We have , the motion of a swing that requires 6 seconds to complete one cycle. Period is the amount of time needed to complete one oscillation . And in question it's given that 6 seconds is needed to complete one cycle. Hence ,Period of the motion of a swing is 6 seconds . Frequency is the number of vibrations produced per second and is calculated with the formula of 
. SI unit of frequency is Hertz or Hz. We know that time period is 6 seconds so frequency =
⇒ 
⇒ 
⇒
Therefore , Period = 6 seconds and .
Answer:
It is example of Closed system
Diagram B .... light shines through at an angle
Nothing will happen to the magnetic field.
BUT If you're talking about the magnetic force , then when changing the current direction , the direction of the magnetic force will be reversed.
(You'ld like to know :
-Changing direction of current ONLY , reverses the direction of magnetic force.
-Changing direction of Magnetic field only (poles of magnet) , reverses the direction of magnetic force.
-Changing the direction of both , magnetic field and current , doesn't effect direction of magnetic force.)
N.B : Magnetic Force is experienced only when direction of current is PARALLEL to direction of magnetic field .
--> Flemming Left Hand Rule is used to know direction of magnetic force.
Hope This Helps.
