Answer:
B. An electric current into a magnetic field
Explanation:
The generation of electrical power requires relative motion between a magnetic field and a conductor. In a generator, mechanical energy is converted into electrical energy. The electricity produced by most generators is in the form of alternating current.
 
        
                    
             
        
        
        
Answer:
d) -4.0
Explanation:
The magnification of a lens is given by

where
M is the magnification
q is the distance of the image from the lens
p is the distance of the object from the lens
In this problem, we have
p = 50 cm is the distance of the object from the lens
q = 250 cm - 50 cm is the distance of the image from the lens (because the image is 250 cm from the obejct
Also, q is positive since the image is real
So, the magnification is

 
        
             
        
        
        
If you were given distance & period of time, you would be able to calculate the speed.
Hope this helps!