Magnetic Flux

Practice Questions:

Question 1: easy

A flux of \(10^{-3}\text{ Wb}\) passes through a strip having an area \(A = 0.02\text{ m}^2\). The plane of the strip is at an angle of \(60^\circ\) to the direction of a uniform field \(B\). The value of \(B\) is:

1. \(0.1\text{ T}\)

2. \(0.058\text{ T}\)

3. \(4.0\text{ mT}\)

4. None of the above

View Answer

The magnetic flux through the surface is given by \(\phi = B A \sin\theta\). Substituting \(\phi = 10^{-3}\text{ Wb}\), \(A = 0.02\text{ m}^2\), and \(\theta = 60^\circ\), we get \(B = \frac{10^{-3}}{0.02 \times \sin 60^\circ} \approx 0.058\text{ T}\).

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Question 2: easy

Assertion (A): A changing magnetic flux induces an electric field.

Reason (R): An inductor always tends to keep the flux constant.

1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)

2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)

3. (3) (A) is true but (R) is false

4. (4) Both (A) and (R) are false

View Answer

Faraday's Law states a changing magnetic flux induces an electric field. Inductors oppose change in flux, but don't keep it constant. Hence, Assertion is true and Reason is false.

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Question 3: easy

Assertion (A): Magnetic flux is a vector quantity.

Reason (R): Value of magnetic flux cannot be negative.

1. Both A & R are true and the (R) is the correct explanation of the (A)

2. Both A & R are true but the (R) is not the correct explanation of the (A)

3. (A) is true but (R) is false

4. Both (A) and (R) are false

View Answer

Magnetic flux \(\phi = \vec{B} \cdot \vec{A}\) is a scalar quantity (A is false). Also, \(\phi = BA cos\theta\) can be negative when \(cos\theta\) is negative, indicating direction relative to area normal (R is false). Both are false.

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