An electric bulb is suspended over a table at a height of 1 m . The illuminance on the table directly beneath the bulb is 40 lux . The illuminance at a point on the table located 1 m away from the first point will be approximately

Step-by-step solution

The illuminance directly beneath the bulb is given by E₀ = I h^2 Given E₀ = 40 lux and h = 1 m , I = 40 cd . For a point on the table at a distance x = 1 m from the point directly beneath the bulb, the distance from the bulb is r = h^2 + x^2 = 1^2 + 1^2 = 2 m . The angle of incidence satisfies = h r = 1 2 . The illuminance at this point is E = I r^2 Substituting the values, E = 40 ( 1 2 ) ( 2 )^2 = 40 2 2 = 10 2 Since 2 1.414 , E 10 1.414 = 14.14 lux . The illuminance is approximately 14 lux .