Home
Class 12
PHYSICS
A source emits 12.0 J of lightof wavelen...

A source emits 12.0 J of lightof wavelength 620 nm and 8.0 J of light of wavelength 580 nm per second. The relative luminosilty at 620 is 25% and that at 580 nm is 80%. Find a. the total radiant flux, b. the total luminous flux and c. and luminous efficiency.

Text Solution

Verified by Experts

AS. The total radiant flux = Total energy radiated per unit time =12J/s+8J/s=20 J/s=20w.
b. The luminous flux correspoinding to th 12 W of 320 nm radiation is
`0.35x(12W)xx685luen W^-1=2877 lumen.`
Similarly, the luminous flux corresponding to teh 8 W of 580 nm radiation is
`=0.80xx(8W)xx685lumen W^-1 =4384lumen.`
the luminous flux of the source is 2877 lumen +4384 lumen
`7261 lumen ~~7260 lumen.`
c. The luminous efficiency =(Total luminous flux)/(Total radiant flux)`
`=(7260lumen)/(20W)=363 lumen W^-1`
Promotional Banner

Topper's Solved these Questions

  • PHOTOMETRY

    HC VERMA|Exercise Short Answer|8 Videos

  • PHOTOMETRY

    HC VERMA|Exercise Objective 1|11 Videos

  • PHOTOMETRY

    HC VERMA|Exercise Exercises|16 Videos

  • PHOTO ELECTRIC EFFECT AND WAVE PARTICLE DUALITY

    HC VERMA|Exercise Exercise|2 Videos

  • SEMICONDUCTOR AND SEMICONDUCTOR DEVICES

    HC VERMA|Exercise Exercises|35 Videos

Similar Questions

Explore conceptually related problems

How many photons per second does a one watt bulb emit if its efficiency is 10% and the wavelength of light emitted is 500 nm

In figure S is a monochromatic point source emitting light of wavelength lambda=500 nm . A thin lens of circular shape and focal length 0.10 m is cut into two identical halves L_(1) and L_(2) by a plane passing through a diameter. The two halves are placed symmetrically about the central axis SO with a gap of 0.5 mm . The distance along the axis from S to L_(1) and L_(2) is 0.15 m , while that from L_(1) and L_(2) to O is 1.30 m . The screen at O is normal to SO . (a) If the 3^(rd) intensity maximum occurs at point P on screen, find distance OP . (b) If the gap between L_(1) and L_(2) is reduced from its original value of 0.5 mm , will the distance OP increases, decreases or remain the same?

A point sources S emitting light of wavelength 600nm is placed at a very small height h above the flat reflecting surface AB (see figure).The intensity of the reflected light is 36% of the intensity.interference firnges are observed on a screen placed parallel to the reflecting surface a very large distance D from it. (A)What is the shape of the interference fringes on the screen? (B)Calculate the ratio of the minimum to the maximum to the maximum intensities in the interference fringes fromed near the point P (shown in the figure) (c) if the intenstities at point P corresponds to a maximum,calculate the minimum distance through which the reflecting surface AB should be shifted so that the intensity at P again becomes maximum.

The young's double slit experiment is done in a medium of refractive index 4//3 .A light of 600nm wavelength is falling on the slits having 0.45 mm separation .The lower slit S_(2) is covered by a thin glass sheet of thickness 10.4mu m and refractive index 1.5 .the intereference pattern is observed ona screen placed 1.5m from the slits are shown (a) Find the location of the central maximum (bright fringe with zero path difference)on the y-axis. (b) Find the light intensity at point O relative to the maximum fringe intensity. (c )Now,if 600nm light is replaced by white light of range 400 to700 nm find the wavelength of the light that from maxima exactly point O .[All wavelengths in this problem are for the given medium of refractive index 4//3 .Ignore dispersion]

A point source is emitting 0.2 W of ultravio- let radiation at a wavelength of lambda = 2537 Å . This source is placed at a distance of 1.0 m from the cathode of a photoelectric cell. The cathode is made of potassium (Work function = 2.22 eV ) and has a surface area of 4 cm^(2) . (a) According to classical theory, what time of exposure to the radiation shall be required for a potassium atom to accumulate sufficient energy to eject a photoelectron. Assume that radius of each potassium atom is 2 Å and it absorbs all energy incident on it. (b) Photon flux is defined as number of light photons reaching the cathode in unit time. Calculate the photon flux. (c) Photo efficiency is defined as probability of a photon being successful in knocking out an electron from the metal surface. Calculate the saturation photocurrent in the cell assuming a photo efficiency of 0.1. (d) Find the cut – off potential difference for the cell.

A small 10 W source of wavelength 99 nm is held at a distance 0.1 m from a metal surface. The radius of an atom of the metal is approximately 0.05 nm . Find (i) the average number of photons striking an atom per second. (ii) the number of photoelectrons emitted per unit area per second if the efficiency of liberation of photoelectrons is 1%

A monochromatic point source radiating wavelength 6000Å with power 2 watt, an aperture A of diameter 0.1 m and a large 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 flux at the centre of the screen and the photo current 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 flux and photocurrent 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 lens in the aperture).

Monichromatic light of wavelength 632.8 nm Is produced by a helium-neon laser.The power emitted is 9.42 mW. (b)How many photons per second,on the average ,arrive at a target irradiated by this beam ? (Assume the beam to have uniform cross-section which is less than the target area),and (c )How fast does a hydrogen atom have to travel in order to have the same moementum as that of the photon?

Monochromatic light of wavelength 632.8 nm is produced by a helium-neon laser. The power emitted is 9.42 mW. (a) Find the energy and momentum of each photon in the light beam, (b) How many photons per second, on the average, arrive at a target irradiated by this beam? (Assume the beam to have uniform cross-section which is less than the target area), and (c) How fast does a hydrogen atom have to travel in order to have the same momentum as that of the photon?

A prism of refractive index n_(1) & another prism of reactive index n_(2) are stuck together without a gap as shown in the figure.The angle of the prisms are as shown. n_(1)&n_(2) depend on lambda ,the wavelength of light according to n_(1)=1.20+(10.8xx10^(4))/(lambda^(2)) & n_(2)=1.45+(1.80xx10^(4))/(lambda^(2)) where lambda is in nm. (i)Calculate the wavelength lambda_(0) for which rays incident at any angle on the interface BC pass through without bending at that interface. (ii) for light of wavelength lambda_(0) ,find the angle of incidencei on face AC such that the deviation produced by the combination of prism is minimum.