Question 14
If a ray of light is incident on ice from air at an angle of 30
o
, which of the following is true?
(Refractive index of ice = 1.309 and refractive index of air = 1)
A. Angle of refraction = sin
-1
(0.382) and air is denser than ice
B. Angle of refraction = sin
-1
(2.6) and ice is denser than air
C. Angle of refraction = sin
-1
(0.382) and ice is denser than air
D. Angle of refraction = cos
-1
(0.382) and air is denser than air
E. Angle of refraction = tan
-1
(0.382) and ice is denser than air
Correct Answer: C
Explanation:
Light entering from one medium to another medium of a different refractive index bends and this
bending is
governed by Snell’s law. It is given as
μ
1
sin θ
i
= μ
2
sin θ
r
---------------- (1)
Putting the values in equation 1 we get
1 * sin 30
o
= 1.309 x sin θ
r
Or θ
r
= sin
-1
(0.382)
Therefore, angle of refraction is sin
-1
(0.382). Whether a medium is denser or rarer is determined by
the refractive index of the medium. Higher the refractive index, denser will be the medium. Since,
refractive index of ice (1.309) is more than that of air (1), ice is denser than air. Hence, C is the
correct answer option.
Question 15
What is the momentum of a photon of energy 1 eV?
1.23 x 10
-28
kgms
-1
1.87 x 10
-28
kgms
-1
1.6 x 10
-19
kgms
-1
5.33 x 10
-28
kgms
-1
4.5 x 10
-19
kgms
-1
Correct Answer: D
Explanation:
Energy of a photon is given as E = mc
2
-------------- (1)
Equation 1 can be written as E = (mc)c ----------------- (2)
Momentum of a photon is defined as the product of mass and velocity of the photon. It is given as p =
mc --------------- (3)