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Asked by rbhatt16 23rd August 2018, 6:25 PM
Answered by Expert
Answer:
induced emf ξ in the loop-A  is given by, ξ = begin mathsize 12px style negative fraction numerator d phi over denominator d t end fraction end style ,  
φ is the magnetic flux which is given by φ = B×A, where B is magnetic field and A is area of coil.
 
hence we have ξ = - A (dB/dt) .............(1)
 
induced emf ξ in the loop-A, when it is moving towards loop-B is written as, ξ = - A (dB/dt) = -A (dB/dx)(dx/dt) = -Av(dB/dx) ...........(2)
where v is speed of movement of loop-A and x is the distance from the centre of loop-B .
 
Magnetic field B along the axis of loop-B  = begin mathsize 12px style fraction numerator mu subscript o I space R squared over denominator 2 open parentheses x squared plus R squared close parentheses to the power of begin display style bevelled 3 over 2 end style end exponent end fraction end style ,
where R is radius of loop-B, I is the current passing through the loop-B and x is the distance of point  in the axis from centre of loop
 
slope of magnetic field = dB/dx = begin mathsize 12px style negative 3 over 2 mu subscript o I R squared space x space open parentheses x squared space plus space R squared close parentheses to the power of bevelled fraction numerator negative 5 over denominator 2 end fraction end exponent end style
the slope dB/dx is maximum at x, where the function f(x) = begin mathsize 12px style x space open parentheses x squared space plus space R squared close parentheses to the power of bevelled fraction numerator negative 5 over denominator 2 end fraction end exponent end style is maximum. 
the distance x at which the slope of field is maximum can be determined by solving for x in the equation df(x)/dx = 0.
 
It is expected from the student to do this exercise and find that df(x)/dx is maximum at x = R/√2 
 
Since induced emf is proportional to slope dB/dx of magnetic field  and this slope is maximum at x = R/√2,
we can conclude that induced emf in loop-A  is maximum at R/√2 from the center of loop-B
Answered by Expert 24th August 2018, 2:23 PM
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