A closely wound search coil has an area of 3.12 cm2cm2 , 135 turns, and a resistance of 58.8 ΩΩ . It is connected to a charge-measuring instrument whose resistance is 43.4 ΩΩ . When the coil is rotated quickly from a position parallel to a uniform magnetic field to one perpendicular to the field, the instrument indicates a charge of 3.46×10−5 CC

B = 0.08395 T = 83.95 mT

Explanation:

According to the Faraday's law of electromagnetic induction, the induced emf is given as

E = -N (dΦ/dt)

The minus sign indicates that the emf is induced in a direction opposite to the changing magnetic flux.

Magnitude of emf is

E = N (dΦ/dt)

From Ohm's law

E = IR

But I = (dQ/dt)

E = R (dQ/dt)

N (dΦ/dt) = R (dQ/dt)

N dΦ = R dQ

Integrating both sides,

NΦ = RQ

But, Φ = BA

N BA = RQ

B = (RQ/NA)

R = 58.8 + 43.4 = 102.2 Ω

Q = (3.46×10⁻⁵) C

A = 3.12 cm² = (3.12 × 10⁻⁴) m²

N = 135

B = (102.2 × 3.46×10⁻⁵)/(135 × 3.12 × 10⁻⁴)

B = 0.0839534663 T = 0.08395 T = 83.95 mT

Hope this Helps!!!

r=rho l/a where a is the area, l is the length and rho is resistivity so the greater the area the lesser the resistance thats why the earth pin is thicker bcos current follow the shortest path, so less resistive .

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