Question

At what distance from a screen will a 27 Cd lamp provide the same illumination as a 75 Cd lamp 15m from the screen ?​

Answer 1

Answer:

P1=27cd, P2=75cd, r2=15m, r1=?

P1/r1^2=P2/r2^2

based on this

r1^2=27*15*15*/75

=81=9^2

r1=9m

Explanation:

m

Answer 2

Given: A 27 Cd lamp provides the same illumination as a 75 Cd lamp 15m from a screen.

To find: The 27 Cd lamp will provide the same illumination at what distance from the screen.

Solution:

• Illumination produced from a light source is directly proportional to the square of the distance between the source and the screen.
• The illumination decreases with an increase in distance between the source and the screen.
• Let x be the distance of the 27 Cd lamp from the screen.
• Hence, the value of x can be calculated as follows,

        $\frac{27 Cd}{x^{2}} = \frac{75 Cd}{(15 m)^{2} }$

        $x = 9 m$

Therefore, the 27 Cd lamp will provide the same illumination at a 9 m distance from the screen.