Answer:
Explanation:
They need a galvanic difference. Or saying that less technically,  they need to have different electron attraction, so that one can collect electrons (oxidation/reduction)  and flow current from the other.  :)
 
        
             
        
        
        
Complete question:
What is the peak emf generated by a 0.250 m radius, 500-turn coil is rotated one-fourth of a revolution in 4.17 ms, originally having its plane perpendicular to a uniform magnetic field 0.425 T. (This is 60 rev/s.)
Answer:
The peak emf generated by the coil is 15.721 kV
Explanation:
Given;
Radius of coil, r = 0.250 m
Number of turns, N = 500-turn
time of revolution, t = 4.17 ms = 4.17 x 10⁻³ s
magnetic field strength, B = 0.425 T
Induced peak emf = NABω
where;
A is the area of the coil
A = πr²
ω is angular velocity
ω = π/2t = (π) /(2 x 4.17 x 10⁻³) = 376.738 rad/s =  60 rev/s
Induced peak emf = NABω
                                = 500 x (π x 0.25²) x 0.425 x 376.738
                                = 15721.16 V
                                = 15.721 kV
Therefore, the peak emf generated by the coil is 15.721 kV
 
        
             
        
        
        
Another (slightly more technical) name for kidney stones is "renal calculus".
I know this because we have met many times, and we are old friends.
 
        
                    
             
        
        
        
v = speed of car = 90 km/h
u = speed of truck = 50 km/h
d = initial separation distance = 100 m = 0.1 km
 
They meet at time t such that
 
vt = d + ut
 
t(v - u) = d
 
t = d/(v - u) = (0.1 km) / [(90 - 50) km/h] = 0.0025 hours