Answer:
(C) Only if it starts moving
Explanation:
We know that work done is given by

So there are two case in which work done is zero 
First case is that when force and displacement are perpendicular to each other 
And other case is that when there is no displacement 
So for work to be done there must have displacement, if there is no displacement then there is no work done 
So option (c) will be the correct option 
 
        
             
        
        
        
Answer:
0.075 T
Explanation:
When a current-carrying wire is immersed in a region with magnetic field, the wire experiences a force, given by

where
I is the current in the wire
L is the length of the wire
B is the strength of the magnetic field
 is the angle between the direction of I and B
 is the angle between the direction of I and B
In this problem we have:
L = 0.65 m is the length of the wire
I = 8.2 A is the current in the wire
F = 0.40 N is the force experienced by the wire
 since the current is at right angle with the magnetic field
 since the current is at right angle with the magnetic field
Solving the formula for B, we find the strength of the magnetic field:

 
        
             
        
        
        
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