(i) Due to ageing, ciliary muscles becoming weak and the eye-lens becoming rigid (inflexible), the eye loses its power of accommodation.
(ii) Because of this, an aged person cannot see the nearby objects clearly. So, it is also called as 'old age hypermetropia'.

(i) The red colour has longer wavelength.
(ii) So, it can travel for longer distance and will be seen clearly. So red colour is used in traffic signals.

(i) The focal length of eye lens is reduced or the distance between eye lens and retina increases.
(ii) Hence the far point will not be infinity for such eyes and the far point has come closer, with this defect, nearby object can be seen clearly but distant objects cannot be seen clearly.

The ratio of speed of light in vacuum (c) to the speed of light in a medium (v) is defined as refractive index (μ) of that medium.
\(\mu=\frac{c}{v}\)

(i) Light is a form of energy.
(ii) Light always travels along a straight line.
(iii) Light does not need any medium for its propagation. It can even travel through vacuum.
(iv) The speed of light in vacuum or air is, c = 3 x 10⁸ m/s
(v) Since, light is in the form of waves, it is characterized by a wavelength (λ) and a frequency (v), which are related by the following equation: c = v λ (c - velocity of light).

(c) Assertion is true but reason is false

(c) Assertion is true but reason is false

(c) Assertion is true but reason is false

According to optical property, it is classified into two types.
(i) Refracting telescope
(ii Reflecting telescope
(i) Refracting telescope: Lenses are used in this kind of telescopes. Galilean telescope, Keplerian telescope, Achromatic refractors, Apochromatic refractors are some Refracting telescope.
(ii) Reflecting telescope: Parabolic mirrors are used in these kind telescopes. Gregorian, Newtonian, Cassegrain telescope, Ritchey- Chretien telescope are some Reflecting telescopes. According to the things which are observed, Astronomical Telescope and Terrestrial Telescopes are the two major types of telescope.

(i) The object is always placed on the left side of the lens.
(ii) All the distances are measured from the optical centre of the lens.
(iii) The distances measured in the same direction as that of incident light are taken as positive.
(iv) The distances measured against the direction of incident light are taken as negative. (v) The distances measured upward and perpendicular to the principal axis is taken as positive.
(v) The distances measured downward and perpendicular to the principal axis is taken· as negative.

(i) First law of refraction : The incident ray of light, the refracted ray of light and the normal to the refracting surface all lie in the same plane.
(ii) Second law of refraction : The ratio of the sine of the angle of incidence and sine of the angle of refraction is equal to the ratio of refractive indices of the two media. This law is also known as Snell's law.
\(\frac{\operatorname{sin i}}{\sin x}=\frac{\mu_2}{\mu_1} .\).