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Fundamentals Of Physics
Found in: Page 896

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Short Answer

One hundred turns of (insulated) copper wire are wrapped around a wooden cylindrical core of cross-sectional area 1.20×10-3m2. The two ends of the wire are connected to a resistor. The total resistance in the circuit is 13.0Ω. If an externally applied uniform longitudinal magnetic field in the core changes from 1.60 T in one direction to 1.60 T in the opposite direction, how much charge flows through a point in the circuit during the change?

The charge flowing through a point in the circuit during the change in magnetic field is, q(t)=2.95×10-2C

See the step by step solution

Step by Step Solution

Step 1: Given

  1. Cross-sectional area, A=1.20×10-3m2
  2. Resistance, R=13.0Ω
  3. Magnetic field at core, B (0) = 1.60 T
  4. Magnetic field at other end in opposite direction, B (t) = (-1.60 T)

Step 2: Determining the concept

The magnetic flux φB through area A in a magnetic field is given by Faraday’s law of induction. If the magnetic field B is perpendicular to the area A, then substitute the given values in the formula to find the charge.

Faraday's law of electromagnetic induction states, Whenever a conductor is placed in a varying magnetic field, an electromotive force is induced in it.

Formulae are as follows:

emf=-N.dφdt

Where, dΦ is magnetic flux, N is number of turns, dt is time.

Step 3: Determining the charge flowing through a point in the circuit during the change in magnetic field

According to Faraday’s law,

emf=-N.dφdt

From Ohm’s law, emf = i.R and i = dq/dt

i.R=-N.dφdt

dqdt=-N.dφdt

Integrating this with respect to time,

qt0t=-Nφt0t

To calculate the charge flowing through the point,

qt=NRφB0-φBt

According to Faraday’s law, if the magnetic field B is perpendicular to the area A, then,

φB=BA

Therefore,

qt=NARB0-Btqt=100×1.20×10-3m213.0Ω16.0 T--1.60 Tqt=100×0.0923×10-3m2×3.20qt=2.95×10-2C

Hence, the charge flowing through a point in the circuit during the change in magnetic field is, q(t)=2.95×10-2C

Therefore, the charge flow through a point in the circuit during the change in the magnetic field can be found by using Faraday’s law.

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