A very long solenoid with a circular cross section and radius r1= 2.40 cm with n
ID: 1455182 • Letter: A
Question
A very long solenoid with a circular cross section and radius r1= 2.40 cm with ns= 220 turns/cm lies inside a short coil of radius r2= 4.00 cm and Nc= 44 turns. If the current in the solenoid is ramped at a constant rate from zero to Is= 1.60 A over a time interval of 55.0 ms, what is the magnitude of the emf in the outer coil while the current in the solenoid is changing? What is the mutual inductance between the solenoid and the short coil? Now reverse the situation. If the current in the short coil is ramped up steadily from zero to Ic= 2.30 A over a time interval of 30.0 ms, what is the magnitude of the emf in the solenoid while the current in the coil is changing?Explanation / Answer
magnetic field due to solenoid B = uo*ns*I
flux through the coil = Nc*B*A = Nc*uo*ns*I*pi*r2^2
emf = (d/dt)*flux
emf = Nc*uo*ns*(dI/dt)*pi*r2^2
emf e = 44*4*pi*10^-7*22000*(1.6/0.055)*pi*0.04^2 = 0.178 V
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M = phi/I = Nc*uo*ns*pi*r2^2
M = 44*4*pi*10^-7*22000*pi*0.04^2
M = 0.00611 Henry
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magnetic field due to ring B = Nc*uo*I/(2*r2)
flux through the coil = ns*B*A = ns*Nc*uo*I/(2*r2)
emf = (d/dt)*flux
emf = ns*Nc*uo*(dI/dt)*pi*r1^2/(2*r2)
emf e = 22000*44*4*pi*10^-7*(2.3/0.03)*pi*0.024^2 = 0.168 V