Question

A perfectly reflecting mirror has an area of 1 cm2. Light energy is allowed to fall on it for one hour at the rate of 10 W/cm2. The force that acts on the mirror is: 

Solution

Correct option is

 

E = energy falling on the surface per sec = o10 J

Momentum of photons.   

                              

On reflection,   

        Change in momentum per sec = 2p = 2E/c

We know that,

        Change in momentum per second = force

.

SIMILAR QUESTIONS

Q1

A ray of light from a denser medium strikes a rarer medium at an angle of incidence i. If the angle of reflection is r and the angle of refraction is r’and reflected and refracted rays make an angle of 90o with each other, then the critical angle will be: 

Q2

The wavelength of light diminishes μ times in the medium. A diver from inside water (μ = 1.33) looks at an object whose natural colour is green. He sees the object as: 

Q3

Air has refraction index of 1.0003. The thickness of air column, which will have one more wavelength of yellow light (6000 Å) than in the same thickness of vacuum is: 

Q4

A ray of light travelling inside a rectangular glass block of refractive index  is incident on the glass-air interface at an angle of incidence of 45o. The refractive index of air is one. Under these conditions the ray:

Q5

The critical angle of for light going from medium x into medium y is θ. The speed of light in medium x is v. The speed of light in medium y is:     

Q6

Monochromatic light of wavelength  travelling in a medium of refractive index n1 enters a denser medium of refractive index n2. The wavelength in the second medium is:    

Q7

When seen in green, the saffron and green portions of our national flag will appear to be: 

Q8

Light travels through a glass plate of thickness t and having refractive indexμ. If c be the velocity of light in vacuum, the time taken by the light to travel this thickness of glass is:

Q9

 are the electric permittivity and the magnetic permeability in a free space, ε and μ are the corresponding quantities in the medium, the index of refraction of the medium is:

Q10

A point source of light is placed 4 m below the surface of water of refractive index 5/3. The minimum diameter of a disc, which should be placed over the source, on the surface of water to cut off all light coming out of water is: