Ray Optics Test...

A lamp is hanging at a height of 4m above a table. The lamp is lowered by lm. The percentage increase in illuminace will be

The intensity of direct sunlight on a surface normal to the rays is I₀. What is the intensity of direct sunlight on a surface, whose normal makes an angle of 60° with the rays of the sun

Inverse square law for illuminance is valid for

1% of light of a source with luminous intensity 50 candela is incident on a circular surface of radius 10 cm. The average illuminance of surface is

Two light sources with equal luminous intensity are lying at a distance of 1.2 m from each other. Where should a screen be placed between them such that illuminance on one of its faces is four times that on another face

A screen receives 3 watt of radiant flux of wavelength 6000 Å. One lumen is equivalent to 1.5 × 10^–3watt ofmonochromatic light of wavelength 5550 Å. If relative luminosity for 6000 Å is 0.685 while that for 5550 Å is 1.00, then the luminous flux of the source is

A point source of 3000 lumen is located at the centre of a cube of side length 2m. The flux through one side is

A point source of light moves in a straight line parallel to a plane table. Consider a small portion of the table directly below the line of movement of the source. The illuminance at this portion varies with its distance r from the source as

A square of side 3 cm is placed at a distance of 25 cm from a concave mirror of focal length 10cm. The centre of the square is at the axis of the mirror and the plane is normal to the axis. The area enclosed by the image of the square is

Short linear object of length 1 lies along the axis of a concave mirror of focal length 1 at a distance u from the pole of the mirror. The size of the image is approximately equal to