Ray optics

1. The speed of light in an isotropic medium depends on,

• Its intensity

• Its wavelength

• The nature of propagation

• The motion of the source w.r.t medium

2. A rod of length 10 cm lies along the principle axis of a concave mirror of focal length 10cm in such a way that its end closer to the pole is 20 cm away from the mirror. The length of the image is,

• 2.5 cm

• 5 cm

• _{10 cm}

• 15 cm

Answer explanation

1/f = 1/u + 1/v

1/v = 1/f - 1/u

1/v = (1/-10 )- (1/-30)

V = 15 cm

Length of imageA^' B^' =20 -15 = 5 cm

3. Stars twinkle due to

• Reflection

• Refraction

• Total internal reflection

• Polarisation

4. An object is placed in front of a convex mirror of focal length of f and the maximum and minimum distance of an object from the mirror such that the image formed is real and magnified

• 2f and c

• c and infinity

• f and o

• None of the above

Answer explanation

In convex mirror, erect and virtual image only formed

5. For light incident from air on a slab of refractive index

2 , the maximum possible angle of refraction is,

• 30⁰

• 45⁰

• 60⁰

• 90⁰

Answer explanation

Mu = sin i / sin r

Sin r=1 /2

r = 30⁰