Multiple-Choice Homework Problem 13.6 A simple generator is constructed by rotat
ID: 1460791 • Letter: M
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Multiple-Choice Homework Problem 13.6 A simple generator is constructed by rotating a flat coil in a uniform magnetic field. Suppose we rotate a flat coil of radius 2.0cm and 400 turns in the earths magnetic field 6 times per second so that the surface normal to the coil is parallel to the field once per revolution. The eartWs magnetic field is still about 4 x 10^5T. What is the maximum emf that would be measured across this generator. Select One of the Following: Multiple-Choice Homework Problem 13.7 You wish to build a time delay circuit using a 75H inductor. You want the voltage across the inductor to fall to 3.0V from an initial voltage of 12V in a period of 2.Os. What resistance must be used in the circuit? Select One of the Following:Explanation / Answer
13.6) d) 7.6*10^-4 V
no of turns, N = 400
Area of the loop, A = pi*r^2
= pi*0.02^2
= 1.257*10^-3 m^2
frequency, f = 6 hz
angular frequency, w = 2*pi*f
= 2*pi*6
= 37.7 rad/s
B = 4*10^-5 T
maximum induced emf = N*A*B*w
= 400*1.257*10^-3*4*10^-5*37.7
= 7.6*10^-4 V
13.7) d) 52 ohms
Let T is the time constant of the circuit.
we know, voltage across inductor at time t,
V = Vmax*e^(-t/T)
3 = 12*e^(-t/T)
3/12 = e^(-t/T)
0.25 = e^(-t/T)
ln(0.25) = -t/T
T = -t/ln(0.25)
= -2/ln(0.25)
= 1.4426 s
we know, T = L/R
==> R = L/T
= 75/1.4426
= 52 ohms <<<<<---------Answer
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