[1 Mark Question Answer]

Question 11 Mark

Write the names of all the components of electromagnetic spectrum in the order of increasing frequency.

Answer

The components of electromagnetic spectrum in the order of increasing frequency are : Radio waves, television waves, microwaves, infrared rays, visible light, ultraviolet light, X-rays and gamma rays.

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Question 21 Mark

A stone placed at the bottom of a water tank appears raised by 80 cm . If the refractive index of water is $4 / 3$, find the actual depth of water in the tank.

Answer

Let the real depth of the water tank $=x cm$
Apparent depth $=(x-80) cm$
We know, $\mu=\frac{\text { Real depth }}{\text { Apparent depth }}$ or $\frac{4}{3}=\frac{x}{x-80}$
or $\quad 4 x-320=3 x$, or $x=320 cm$

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Question 31 Mark

The angle of refraction in a glass block of refractive index $1.5$ is $19^{\circ}$. Calculate the angle of incidence.

Answer

$\mu=\frac{\sin i}{\sin r}$
$\therefore \sin i=\mu \times \sin r=1.5 \times \sin 19^{\circ}=1.5 \times 0.325=0.4875$
$\sin i=0.4875$
$\therefore i=\sin ^{-1}(0.4875)=29.18^{\circ} \text { (approx.) }$

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Question 41 Mark

(a) Define critical angle.
(b) State one important factor which affects the critical angle of a given medium.

Answer

(a) Critical angle: Angle of incidence in a denser medium for which the angle of refraction in the rarer medium is $90^{\circ}$ is called critical angle.
(b) The colour (or wavelength) of light.

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Question 51 Mark

(a) Define refractive index of a medium in terms of velocity of light.
(b) Can the absolute refractive index of a medium be less than one?

Answer

(a) Refractive index of a medium is the ratio of velocity of light in vacuum or air to the velocity of light in a given medium.
(b) Yes, when a ray travels from glass (or any denser medium) to air, the absolute refractive index of air is less than 1.

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Physics [1 Mark Question Answer]

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