Question

A clock hung on a wall has marks instead of numerals on its dial. On the adjoining wall, there is a plane mirror and the image of the clock in the mirror indicated the time 7.10. Then the time on the clock is: 

Solution

Correct option is

4.50

 

The image in a plane mirror undergoes depth inversion; hence the time on the image is as much ahead of 12 hours zero minutes as the time on actual clock is behind 12 hours zero minutes.  

Time on the actual clock = 7 hours 10 minutes   

Time on the image clock

                     = (12 hrs and zero minutes) – (7 hrs and 10 minutes)

                     = 4 hrs and 50 minutes.

SIMILAR QUESTIONS

Q1

When a ray of light enters a glass slab from air:

Q2

How many images of himself does an observer see if two adjacent walls and the ceiling of a rectangular room are mirror surfaced?

Q3

Mirage is a phenomenon due to:

Q4

A plane glass slab is kept over various coloured letters; the letter which appears least raised is:

Q5

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: 

Q6

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: 

Q7

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: 

Q8

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:

Q9

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:     

Q10

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: