1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Q. 145.0( 1 Vote )

Figure (22-E1) shows a small diffused plane source S placed over a horizontal table-top at a distance of 24 m with its plane parallel to the table-top. The illuminance at the point A directly below the source is 25 lux. Find the illuminance at a point B of the table at a distance of 18 m from A.

Class 11th HC Verma - Concepts of Physics Part 1 22. Photometry

Answer :

In triangle ABS,

AS =2.4 m

AB = 1.8 m.

Hence BS = √(2.4²+1.8²) = √9 = 3 m.

Let, ,

Illuminance at A = 25 lux.

Let the intensity along SA =.

Since it is a small extended source, from Lambert's cosine law, the intensity along SB:

I

.

The angle between SB and normal at B is also θ.

Hence the illuminance at B,

Rate this question :

How useful is this solution?

We strive to provide quality solutions. Please rate us to serve you better.

PREVIOUSA student is studying a book placed near the edge of a circular table of radius R. A point source of light is suspended directly above the center of the table. What should be the height of the source above the table so as to produce maximum illuminance at the position of the book?NEXTAn electric lamp and a candle produce equal illuminance at a photometer screen when they are placed at 80 cm and 20 cm from the screen respectively. The lamp is now covered with a thin paper which transmits 49% of the luminous flux. By what distance should be lamp be moved to balance the intensities at the screen again?

Try our Mini CourseMaster Important Topics in 7 DaysLearn from IITians, NITians, Doctors & Academic Experts

Dedicated counsellor for each student

24X7 Doubt Resolution

Daily Report Card

Detailed Performance Evaluation

caricature

view all courses

RELATED QUESTIONS :

A point source emitting light uniformly in all directions is placed 60 cm above a table-top. The illuminance at a point on the table-top, directly below the source, is 15 lux. Find the illuminance at a point on the table-top 80 cm away from the first point.

HC Verma - Concepts of Physics Part 1

A student is studying a book placed near the edge of a circular table of radius R. A point source of light is suspended directly above the center of the table. What should be the height of the source above the table so as to produce maximum illuminance at the position of the book?

HC Verma - Concepts of Physics Part 1

The illuminance of a small area changes from 900 lumen to 400 lumen when it is shifted along its normal by 10 cm. Assuming that it is illuminated by a point source placed on the normal, find the distance between the source and the area in the original position.

HC Verma - Concepts of Physics Part 1

A point source emitting 628 lumen of luminous flux uniformly in all directions is placed at the origin. Calculated the illuminance on a small area placed at (10 m, 0, 0) in such a way that the normal to the area makes an angle of 37° with the X-axis.

HC Verma - Concepts of Physics Part 1

Figure (22-E1) shows a small diffused plane source S placed over a horizontal table-top at a distance of 24 m with its plane parallel to the table-top. The illuminance at the point A directly below the source is 25 lux. Find the illuminance at a point B of the table at a distance of 18 m from A.

HC Verma - Concepts of Physics Part 1