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Friend’s Shadow forms on the wall.

Cones are said to be the cells of the retina that are responsible for producing colour sensation.

The small droplets of rain water which remain suspended in air just after the rains act like a prism. When sunlight passes through these drops of rainwater, it gets dispersed and we see the seven colours of the rainbow.

Light comes from different objects called sources of light. 

Ex : 

Sun, candle, tube light.

No, we cannot see all these objects during night time.

The deviation in the path of light when it passes from one medium to another medium of different density is called refraction.

The spherical mirror which has reflecting surface bent inward is called concave mirror.

Lens which is thick in center and thin at the edges is called convex lens.

A lens which is thicker in the middle and thinner at the edges is called a convex lens.

In a convex lens at least one of its surfaces is bulging out at the middle.

There are two types of lenses are :

Convex lens or converging lens.

Concave or diverging lens.

A lens is a portion of a transparent refracting medium bounded by two surfaces which are generally spherical or cylindrical or one curved and one plane surface.

The refractive index of a medium depends on the following factors:

The nature of the medium.

The colour or wavelength of the incident light.

Concave mirrors are used by dentists, ophthalmologists, ENT doctors and also in head lights of vehicles.

It is used in spectacles for correcting myopia.

Along with convex lens it is used to overcome defects like chromatic aberration and spherical aberration (the failure of rays to converge at one focus because of a defect in a lens or mirror).

The process of splitting of white light into its constituent colours when it is passed through a transparent medium is known as Dispersion of light.

Focal length is the distance between the pole and the focus of a mirror. It is represented by the letter f.

The spherical mirror which has reflecting surface bent outward is called convex mirror.

We do not see the shadow of a bird flying high up in air because in their shadow, the umbra is absent and the penumbra is too large and too faint that it is not visible as the distance of screen (i.e. earth) is very large from the object (i.e. bird).

No. Shadow of the bird can only be seen when the bird is flying very low close to the ground.

Translucent objects cast a faint shadow whereas transparent objects do not cast a shadow at all because they allow light to pass through them.

(a) Incident tavi The ray of light that falls on the surface of the reflection materials. 

(b) Reflected ray: The ray of light that comes from the point when the incident ray falls on the reflection material. 

(c) Normal: The perpendicular line drawn from, the point of incidence to the plane of reflecting surface is called normal. 

(d) Angle of incidence The angle formed between the incident ray PO and the normal ‘ON’ is angle of incidence.

Eclipses are the examples of formation of shadows in nature. There are two kinds of eclipses: 

1. Lunar eclipse (the eclipse of the moon), and 

2. Solar eclipse (the eclipse of the sun). Lunar eclipse is due to the formation of shadow of earth on moon and solar eclipse is due to the formation of shadow of moon on earth.

Light travels in a straight line path. This is called the rectilinear propagation of light.

Take three cardboards A, B and C each about 25 cm square. Take a pin and make a small hole in each cardboard at the same height. Suspend the cardboard pieces by separate threads vertically from a support such that each hole is at the same height, as shown. Pass a string through the holes and pull it taut. This makes the three holes in a straight line. Now take out the string. 

Place a lighted candle near one of the cardboards (say A). Look at the candle flame from the other side of the cardboard C. The candle flame is clearly seen. Now slightly displace one of the cardboards (say B) so that the holes no longer remain in a straight line. Again look at the candle flame from the other side of the cardboard C. You do not see the candle flame. The reason is that light travels in a straight line and now the holes in the cardboards A, B and C are not in a straight line. 

Conclusion: Light travels in a straight line path called the rectilinear propagation of light.

a) Regular reflection occurs from a cinema screen because the surface of the screen is smooth. 

b) Regular reflection occurs from a plane mirror because the surface of a plane mirror is smooth even.

Virtual image is formed by an extension of reflected ray where the ray never meets in real.

That is a reason virtual image cannot be taken on screen.

(a) For rough surface irregular reflection or diffused reflection takes place.

(b) For smooth surface regular reflection takes place.

The object would be 15 cm far away from its image if it is placed at a distance of 7.5 cm from the plane mirror.

The object is at 7.5 cm from the mirror, then the image of the object is 7.5 cm on the other side of the mirror. Hence, the image is a total of 15 cm from object (7.5 cm to the mirror + 7.5 cm to the image).

Image formed by an object in a plane mirror is virtual because the image from behind the mirror and we cannot take this image on a screen.

Speed of light in vacuum is 3×10⁸ m/s.

The image of an object in a plane mirror is virtual. Virtual image cannot be projected onto the screen because it is not real.

A virtual image is a copy of the object, formed on the plane mirror. The light rays never come from the image. They appear to come from the object.

The phenomenon is known as Lateral inversion. The effect produced by a plane mirror in reversing the images from left to right and right to left while forming images is lateral inversion.

The angle of reflection when a ray of light is incident normally on a plane mirror will be zero degree because the angle of incidence will be zero degree as the ray is incident normally. By law of reflection, angle of incidence = angle of reflection.

The angle of incidence when a ray of light is incident normally on a plane mirror is zero degree because the ray is incident normally.

Infinite number of images will be formed if a candle is placed between two parallel mirrors