A battery operated tourch is adjusted to send and almost parallel beam of light. It produces an illuminance of 40 lux when the light falls on a wal 2m away. The illuminance produced when it fals on a wal 4 m away is close to

A point source of light produces an illumination I at a point. When the distance between them is made four times its original value, the intensity at that point becomes

An electric bulb is hanging over a table at a height of 1 m above it. The illuminance on the table directly below the bulb is 40 lux. The illuminance at a point on the table 1 m away from the first point will be about

An electric bulb is hanging over a table at a height of 1 m above it. The illuminance on the table directly below the bulb is 40 lux. The illuminance at a point on the table 1 m away from the first point will be about

An electric bulb is hanging over a table at a height of 1 m above it. The illuminance on the table directly below the bulb is 40 lux. The illuminance at a point on the table 1 m away from the first point will be about

Rays of light from a source of luminous intensity 40 cd are incident at 60^@ on a screen placed 2 m from the source. Illumination produced on the screen is (lux)

Two parallel slits 0.6mm apart are illuminated by light source of wavelength 6000Å . The distance between two consecutive dark fringe on a screen 1m away from the slits is

A photocell is illuminated by a small bright source places 1 m away when the same source of light is placed (1)/(2) m away. The number of electron emitted by photocathode would be

Figure shows a small diffused plane source S placed over a horizontal table-top at a distance of 2.4 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 1.8 m from A.

Figure shows a small diffused plane source S placed over a horizontal table-top at a distance of 2.4 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 1.8 m from A.

A photoelectric cell is illuminated by a point source of light 1m away. When the source us shifted to 2m then-