1. A coil of 100 turns and radius 15.0 cm surrounds a long solenoid of radius 2.

Question

1. A coil of 100 turns and radius 15.0 cm surrounds a long solenoid of radius 2.5 cm and 2000 turns/metre. The current in the solenoid changes as I = (10.0 A) sin(377t). What is the maximum value of the induced electric field in the 100-turn coil? (15.4 mV/m, 19.7 mV/m, 22.4 mV/m, 25.4 mV/m)

2. What is the value of the net flux of a magnetic field through a closed surface? (0, equal to magnitude of the magnetic field divided by permeability of free space, equal to square of the magnitude of the magnetic field divided by the permeability of free space, infinite).

3. How does the magnetic field between the plates of a capacitor change with respect to time after the conduction current stops flowing?

Magnetic field is zero after the current stops flowing.

Magnetic field first increases and then decreases.

Magnetic field stays constant.

It depends on the capacitance.

Magnetic field is zero after the current stops flowing.

Magnetic field first increases and then decreases.

Magnetic field stays constant.

It depends on the capacitance.

Explanation / Answer

1. flux = B.A

= (100 x pi x 0.025^2) ( 4pi x 10^-7 x 2000 x 10 sin(377t))

for solenoid, B = u0 n I

flux = (4.935 x 10^-3 ) sin(377t)

e = d(flux)/dt = 1.86 cos(377t)

e_max = 1.86 Volt

E_max = e_max / L = (1.86) / (100 x 2 x pi x 0.15)

= 0.0197 V/m

= 19.7 mV/m

2. through closed surface,

magnetic flux = 0

3. (B)(2 pi r) = u0 Iin

I_in = 0 then B= 0

Ans: Magnetic field is zero after the current stops flowing

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