Question
Hard
Solving time: 5 mins
Q.11. An illuminant shaped as a plane horizontal disc of radius R = 25 cm is suspended over a table at a height h = 75 cm. The illuminance of the table below the centre of the illuminant is equal to E0 = 70 lx. Assuming the source to obey Lambert's law, find its luminosity.
Text solutionVerified
Consider an angular element of area
Light emitted from this ring is
Now,
where dA = an element of area of the table just below the untre of the illuminant Then the illuminance at the element dA will be
where
Finally using luminosity M = πL
or dimensionally)
Light emitted from this ring is
Now,
where dA = an element of area of the table just below the untre of the illuminant Then the illuminance at the element dA will be
where
Finally using luminosity M = πL
or dimensionally)
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Question Text | Q.11. An illuminant shaped as a plane horizontal disc of radius R = 25 cm is suspended over a table at a height h = 75 cm. The illuminance of the table below the centre of the illuminant is equal to E0 = 70 lx. Assuming the source to obey Lambert's law, find its luminosity. |
Topic | Dual Nature of Radiation and Matter |
Subject | Physics |
Class | Class 12 |
Answer Type | Text solution:1 |
Upvotes | 29 |