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A substance through which we cannot see light is called an opaque medium. 

Examples: Wood, metals, butter paper and black paper etc.

The direction or path along which light travels is called a ray of light.

The size of the image in the mirror is the same as that of the object.

Moon is not a luminous body, it is nbn-luminous body. It has no light of its own.

The bodies that shines on its ownor which them selves emit their own light are called the luminous bodies.

The objects beyond the hot air appears to be wavy because the medium for light to pass through changes, the light passes from denser to rarer and then again to denser medium thereby causing refraction in the air. Moreover the refractive index of the hot air keeps changing which leads to give the wavy appearance of the object.

Moon, jugnu.

A Lunar eclipse occurs when earth conies between sun and moon in a straight line.

1. Lunar eclipse occurs, when the Earth (E) comes between the Sun (S) and the Moon (M). 

2. The Earth prevents light coming from the Sun and makes shadow on the Moon. This is lunar eclipse.

Refractive index is defined as the ratio of speed of light in medium 1 to the speed of light in medium 2 and is represented as n₂₁ and is read as refractive index of medium 2 with respect to medium 1. 

n₂₁ = speed of light in medium 1/speed of light in medium 2.

The phenomenon due to which left hand side of object appears as right hand side and vice versa is called lateral inversion.

(b) straight line, shadows

1. Materials that are not able to allow light to pass through, are called opaque material. 

2. Example: Wall, thick card board, stone, etc.

When white light is made to fall on the surface of a prism, it disperses and we obtain a spectrum of light.

the angle of incidence = angle of reflection. 

According to the question, given i + r = 90 degree

i = r

hence i + i = 90 degree

2i = 90 degree.

I = 45 degree. 

Therefore, the angle of incidence is 45 degree.

a) Diffused reflection takes place from a rough surface. The reflected rays are not parallel in diffused reflection. 

b) Regular reflection takes place from a smooth surface. The reflected rays are parallel in regular reflection.

The apparatus used to obtain a thin beam of light is known as Ray box. The rays are bright enough to be viewed easily. A ray box is a standard source of light used in optics experiments.

(a) both A and B

Lateral displacement is the perpendicular distance between the incident ray and the emergent ray.

It has no unit.

In a plain mirror, our right hand appears like left hand of the image. Similarly, our left hand appears like right off the image. This phenomenon is called lateral inversion.

Eye lens reduces transparency and flexibility in cataract.

When all reflected rays are parallel to each other, the reflection is called regular reflection. Clear image is formed in case of regular reflection. When reflected rays are not parallel to each other, the reflection is called irregular reflection. Diffused image is formed in case of irregular reflection,

Light is a form of Energy i. e. The external physical cause that affects our eye to produce the sensation of vision.

Normal – The perpendicular drawn to the reflecting surface is called normal at that point.

As rear view mirror, as mirror on hairpin bends on road .

2. certain full moon’s night

Difference Between 

Luminous 

The bodies which have light of their own e.g. sun stars, bulb, candle, oil lamp, torch, a lantern. 

Non-Luminous 

The bodies-which do not have their own light. E.g. moon, chair, table. When light falls on them, they become visible.

2. certain new moon’s day

Angle of incidence – the angle between the incident ray and the normal is known as angle of incidence.

Angle of reflection – The angle between reflected ray and the normal is known as angle of reflection.

As shaving mirror, as solar cooker.

= \(\frac{1}{u} +\frac{1}{v} =\frac{1}{f}.\)

The angle made by the reflected ray with the normal is called the angle of reflection (r).

The angle made by incident ray with the normal is called angle of incidence (i).

(d) Virtual and erect

(b) Convex mirror