Two lamps balance on the shadow photometer at distance of `0.60 m` and `0.42 m` from the screen. The stronger is then covered with a glass shade whicht transmits `80%` of the incident light. How far must be the other lamp be displaced in order to restore balance?

An 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 the lamp be moved to balance the intensities at the screen again ?

Two stars are situated at a distance of 8 light years from the earth. These are to be just resolved by a telescope of diameter 0.25 m. If the wavelength of light used is 5000 Å, then the distance between the stars must be

Two sources of light are at distance 0.6m and 0.9m on either side of a screen for matching. When a glass plate is introduced between the weaker source and the screen, the other source has to be moved 0.2m farther to match the illumination. Calculate the percentage of the light stopped by the glass plate introduced.

A light of wavelength 6000 Å shines on two narrow slits separeted by a distance 1.0 mm and illuminates a screen at a distance 1.5 m away. When one slit is covered by a thin glass plate of refractive index 1.8 and other slit by a thin glass plate of refractive index mu , the central maxima shifts by 0.1 rad. Both plates have the same thickness of 0.5 mm. The value of refractive index mu of the glass is

Two slits are separated by distance of 0.5 and illuminate with light of lambda=6000Å . If the screen is placed 2.5m from the slits. The distance of the third bright image from the centre will be

Two slits are separated by a distance of 0.5mm and illuminated with light of lambda=6000Å . If the screen is placed 2.5m from the slits. The distance of the third bright image from the centre will be

A monochormatic point source radiating wavelength 6000Å with power 2 vate an aperture A of diameeter 0.1 m and a lorge screen SC are placed as shown in fig, A photoemissive detector D of surface area 0.5 cm^(2) is placed at the centre of the screen . The efficiency of the detector for the photoelectron generation per incident photon is 0.9 (a) Calculate the photon flat at the centre of the screen and the photocurrwect in the detector. (b) If the concave lens L of focal length 0.6 m is inserted in the aperture as shown . find the new values of photon flot and photocurrect Assume a uniform average transmission of 80% from the lens . (c ) If the work function of the photoemissive surface is 1eV . calculate the values of the stopping potential in the two cases (within and with the lelens in the epertuire).

Two light sources of intensities 8 cd and 12 cd are placed on the same side of a photometer screen at a distance of 40 cm from it. Where should a 80 cd source be placed to balance the illuminance ?

A fluorescent lamp of length 1m is placed horizontally at a depth of 1.2 m below a ceiling . A plane mirror of length 0.6 m is placed below the lamp parallel to and symmetric to the lamp at a distance 2.4 m from it as shown in figure. Find the length in meters (distance between the extreme points of the visible region along x -axis ) of the reflected patch of light on the ceiling.