Question

What is the luminous intensity of a lamp which produces an illuminance of 12 lux at a distance of 5.0 m from it?  

Solution

Correct option is

300 cd

 

E = 12 lux and r = 5.0 m. Luminous intensity I is related to E as

                      

.  

SIMILAR QUESTIONS

Q1

A small plane mirror is rotating at a constant frequency of n rotations per second. With what linear velocity (in ms–1) will a light spot move along a spherical screen of radius of curvature of R metres if the mirror is at the centre of curvature of the screen?   

Q2

A ray of light incident normally on face AB of an isosceles prism travels as shown in fig. The least value of the refractive index the prism must have should be    

                                                                        

Q3

A beaker is filled with water to a height of 8.00 cm. The apparent depth of a needle fixed at the bottom of the beaker as measured by a travelling microscope is found to be 6.00 cm. If the height of water in the beaker is increased to 12.0 cm, by what distance would the microscope have to be moved to focus on the needle again?       

Q4

When a thin wedge-shaped film is illuminated by a parallel beam of light of wavelength 6000 Ã…, 7 fringes are observed in a certain region of the film. How many fringes will be observed in the same region of the film if light of wavelength 4200 Ã… is used?

Q5

A parallel beam of white light is reflected from a thin wedge-shaped film. The colour of the fringe at the edge of the wedge will be 

Q6

When a ray of light is incident on a glass slab at an angle of 60o, the angle between the reflected and refracted rays is 90o. The refractive index of glass is  

Q7

The polarising angle for glass is 

Q8

What is the SI unit of luminous intensity?

Q9

What are the dimensions of luminous intensity?   

Q10

To print a photograph from a negative, the time of exposure to light from a lamp placed 60  cm away is 2.5 s. What exposure time is required if the lamp is placed 1.2 m away?