Answer:
When a wire that carries electrical current is placed in a magnetic field the wire experiences a force.
Explanation:
The electric motor is a device which convert electrical energy into mechanical energy  ie when current carrying conductor is placed in magnetic field it experience a force. Flemings left hand rule explains the direction of the current.
The electric motor works by attraction and repulsion of magnetic field.
So the option d explains basic concept of simple motor ie when when current carrying wire is placed in the magnetic field it experience magnetic repulsive force.
 
        
             
        
        
        
It would be 12hz because it
        
                    
             
        
        
        
Answer
given,
D = 50 mm = 0.05 m
d = 10 mm = 0.01 m
Force to compress the spring




      F = 3160 N
stress correction factor from stress correction curve is equal to 1.1
now, calculation of corrected stress


               = 442.6 Mpa
The tensile strength of the steel material of  ASTM A229 is equal to 1300 Mpa
now,



since corrected stress is less than the  
 
hence, spring will return to its original shape.
 
        
                    
             
        
        
        
V=IR
V=15x11
V=165ohms 
I don’t quite remember the unit
Ohms law