Question

In the phenomenon of interference, energy is

• A. destroyed at bright fringes
• B. created at dark fringes
• C. conserved, but it is redistributed
• D. same at all points

Answer 1

The correct option is C

conserved, but it is redistributed

The explanation for the Correct Option:

Option (C):

1. An important consequence of the principle of superposition is that when two beams of light intersect, the propagation of each beam is completely unaffected by the presence of the other.
2. However, in the region of crossing both the beams act simultaneously and we expect a change in intensity.
3. A case of utmost importance occurs when monochromatic waves of light from two sources proceed almost in the same direction and superpose at a point either in the same or in the opposite phase.
4. Then the intensity of light at a point that point will be maximum or minimum according to as the waves meet the point in the same or in the opposite phase.
5. This phenomenon is known as interference of light.
6. Hence, the energy is conserved but redistributed among bright and dark fringes.

The explanation for Incorrect Option:

Option (A):

1. We know that intensity is directly proportional to the energy.
2. For constructive interference, intensity is maximum, so energy here will also be maximum.
3. Hence, in the phenomenon of interference, energy is created at bright fringes.

Option (B):

1. We know that intensity is directly proportional to the energy.
2. For destructive interference, intensity is minimum, so energy here will also be minimum.
3. Hence, in the phenomenon of interference, energy is destroyed at dark fringes.

Option (D):

1. For interference waves of light from two sources proceed almost in the same direction and superpose at a point either in the same or in the opposite phase.
2. Then the intensity of light at a point that point will be maximum or minimum according to as the waves meet the point in the same or in the opposite phase.
3. We know that intensity is directly proportional to the energy.
4. Hence, the energy cannot be the same at all points.

Hence option C is correct.