JEE MainPhysicsWave OpticsMCQ+4 / −1
A beam of plane polarised light of large cross-sectional area and uniform intensity of 3.3 Wm-2 falls normally on a polariser (cross sectional area 3 10-4 m2) which rotates about its axis with an angular speed of 31.4 rad/s. The energy of light passing through the polariser per revolution, is close to :
- A1.0 10-5 J
- B1.0 10-4 J
- C1.5 10-4 J
- D5.0 10-4 J
View written solutionFree
Correct answer: B
- Given data
- Intensity of incident plane polarised light:
- Area of polariser:
- Angular speed of rotation:
We need the energy transmitted in one complete revolution.
- Instantaneous transmitted intensity
Since the incident light is plane polarised and the polariser rotates, the transmitted intensity is given by Malus' law:
where
So,
- Instantaneous transmitted power
Power transmitted through the polariser is
Substitute values:
- Time for one revolution
For one full revolution,
- Energy transmitted in one revolution
Energy is
Over one full cycle, average value of is
Therefore,
Substitute:
This is approximately
- Option matching
The closest option is:
B:
- Comparison with stored answer
Stored correct answer: B
Our derived answer: B
So they agree.
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