Question

-ELECTROMAGNETIC THEORY (2) (1) The coil shown in the figure has 2 tums, a cross-sectional area of 0.20 m and a field (parallel to the axis of the coll) with a magnitude given by B = (4.0 +3.07") T, where is ins. What is the potential difference, VA -Vaat 3.0 s? Select one 0 - 12v +48V +7:2V - 48V 0 -72V

Answer 1

total flux through the coil is

o= NBA

where, $\phi$ is the flux, N number of turns, B magnetic field and A area

So,

0 = 2 x (4 + 3t) x 0.2 = 1.6+ 1.2

Potentlal difference accross the resistor is equal to emf induced in the coil and is given by,

VA - Vc = €= - - (1.6 +1.2) = -2.4t = 2.4 x 3 = -7.2V

Ans: (E) -7.2V

(numerical value is easy. For the sign positive or negative we ca use Lenz's Law, which states that the induced current will flow in such a way that it will try to cancel out the change that is producing it. Here magnetic field is increasing in the +x direction, and increases flux. So the induced current will produce magnetic field in -x direction so that the increase in flux can be cancelled out. So current will flow from C to A in the resistor. So C will be at higher potential. That is will be negative.)

VA - Va