Question

A uniform magnetic field points directly into your paper (make a sketch). A 7 turn coil of wire with a radius of 14.2 cm lies in the plane of the paper. Over a period of 0.00035 seconds, the field is increased from 0.300 T to 1.10 T. How much emf is induced in the coil while B is changing? A-0.12 volts B- 0.91 volts C-28 volts D- 16,000 volts E- 250 volts Which way is the induced emf (or induced current) in the question above? A- Right B-out of the paper C-left D-clockwise E- Into the paper Recently a star with several possibly earth-like planets was discovered. It is 3x10^18 m from earth. HOw long does it take light from that start to reach earth? A-1.5x10^4 s B-3.2x10^7 C-2.4x10-9 s D- 3x10^8 s E-1x10^10

Answer 1

1)

Emf = - N d$\phi$ / dt

Emf = - N d (BA) / dt

Emf = - NA dB / dt

Emf = - 7 * pi * 0.142² * ( 1.10 - 0.3) / 0.00035

Emf = - 1013.6 Volts

(Options given are definitely wrong)

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as field into the page is increasing, this means flux is increasing. To oppose this increase, an external field is induced out of the page.

so,

emf is counter clockwise

field is into the page х л к к х х x x induced field out of the page x x

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time = distance / speed

time = 3e18 / 3e8

time = 1e10 seconds