PUC Science 2nd PUC Class 12 - Karnataka Board PUC Question Bank Solutions for Physics

As the wavelength is increased from violet to red, the luminosity ____________ .

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 ___________ .

Light from a point source falls on a screen. If the separation between the source and the screen is increased by 1%, the illuminance will decrease (nearly) by ____________ .

A battery-operated torch is adjusted to send an almost parallel beam of light. It produces an illuminancle of 40 lux when the light falls on a wall 2 m away. The illuminance produced when it falls on a wall 4 m away is close to _________ .

The intensity produced by a long cylindrical light source at a small distance r from the source is proportional to _________ .

A photographic plate placed a distance of 5 cm from a weak point source is exposed for 3 s. If the plate is kept at a distance of 10 cm from the source, the time needed for the same exposure is _____________ .

A photographic plate is placed directly in front of a small diffused source in the shape of a circular disc. It takes 12s to get a good exposure. If the source is rotated by 60° about one of its diameter, the time needed to get the same exposure will be ___________ .

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 ___________ .

Figure shows a glowing mercury tube. The intensities at point A, B and C are related as __________ .

The brightness-producing capacity of a source

(a) does not depend on its power

(b) does not depend on the wavelength emitted

(c) depends on its power

(d) depends on the wavelength emitted

A room is illuminated by an extended source. The illuminance at a particular portion of a wall can be increased by

(a) moving the source

(b) rotating the source

(c) bringing some mirrors in proper positions

(d) changing the colour of the source.

Mark the correct options.

(a) The luminous efficiency of a monochromatic source is always greater than that of a white light source of same power.

(b) The luminous efficiency of a monochromatic source of wavelength 555 nm is always greater than that of a white light source of same power.

(c) The illuminating power of a monochromatic source of wavelength 555 nm is always greater than that of a white light source of same power.

(d) The illuminating power of a monochromatic source is always greater than that of a white light source of same power.

Mark out the correct options.

(a) Luminous flux and radiant flux have same dimensions.

(b) Luminous flux and luminous intensity have same dimensions.

(c) Radiant flux and power have same dimensions.

(d) Relative luminosity is a dimensionless quantity.

A source emits 45 joules of energy in 15 s. What is the radiant flux of the source?

A photographic plate records sufficiently intense lines when it is exposed for 12 s to a source of 10 W. How long should it be exposed to a 12 W source radiating the light of same colour to get equally intense lines?

Using figure, find the relative luminosity of wavelength (a) 480 nm, (b) 520 nm (c) 580 nm and (d) 600 nm.

The relative luminosity of wavelength 600 nm is 0.6. Find the radiant flux of 600 nm needed to produce the same brightness sensation as produced by 120 W of radiant flux at 555 nm.

The luminous flux of a monochromatic source of 1 W is 450 lumen watt⁻¹. Find the relative luminosity at the wavelength emitted.

A source emits light of wavelengths 555 nm and 600 nm. The radiant flux of the 555 nm part is 40 W and of the 600 nm part is 30 W. The relative luminosity at 600 nm is 0.6. Find (a) the total radiant flux, (b) the total luminous flux, (c) the luminous efficiency.

A light source emits monochromatic light of  555 nwavelengthm. The source consumes 100 W of electric power and emits 35 W of radiant flux. Calculate the overall luminous efficiency.