Light enters from air into a glass plate of refractive index 1 . 5 . What will be speed of light in glass? (Speed of light in air = 3 × 10 8 ms - 1 )

According to laws of refraction, if a light ray is entering from a rarer to denser medium it will bend towards the normal . The reason why light is bending towards the normal is the lower velocity of light in the denser medium when compared to the rarer medium. Here, light enters from air to glass having a refractive index 1 . 5 , We know the speed of light in a vacuum is 3 × 10 8 ms - 1 . Let us take the speed of light in a vacuum is c , speed of light in glass is v g , Refractive index of glass μ g = c v g ⇒ 1 . 5 = 3 × 10 8 v g ⇒ v g = 3 × 10 8 1 . 5 = 2 × 10 8 ms - 1 .

An object 5 cm in length is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm . Find the position, nature and size of the image.

Given: The Height of the object, h = 5 cm The Object Distance, u = - 20 cm (By using Sign Convention) The Radius of Curvature = 30 cm We know from the relation between the focal length and the radius of curvature, Focal Length, f = R 2 = 15 cm (By using Sign Convention) Using Mirror Formula: 1 f = 1 u + 1 v 1 v - 1 20 = 1 15 1 v = 1 15 + 1 20 v = 60 7 = 8 . 57 cm The image distance is 8 . 57 cm behind the convex mirror. As the v is positive, the image formed is virtual and erect. From the magnification formula, m = - v u = - 8 . 57 - 20 = 0 . 42 cm This indicates that the image is diminished because the magnification of the image is less than 1 . Position of Image: Behind the mirror. Nature of Image: Virtual and Erect.

The refractive index of water is 1 . 33 . What is the meaning of this statement?

The refractive index is 1 . 33 of the water means that the speed of light in the water will be 1 / 1 . 33 times the speed of light in a vacuum. Note: Refractive index of a medium is the ratio of the speed of light in a vacuum to its speed in a specified medium.

Find the focal length of a lens of Power 2 . 5 D .

Given, The power of the lens, P = + 2 . 5 D The degree of convergence or divergence of light rays achieved by a lens is expressed in terms of its power. We know that the power in Dioptre is the reciprocal of the focal length in metre. Therefore, the focal length, f = 1 P f = 1 2 . 5 f = 0 . 4 m = 40 cm

Write two uses of Concave mirror.

A concave mirror, also called a converging mirror, has its reflecting surface bulging inward, i.e. away from the incident light. The uses of the concave mirror are as follows: Shaving mirror: A concave mirror produces a virtual and magnified image when it is placed nearby the object. Hence, is it is used for shaving purposes to view enlarged beards. Vehicle headlights: In the vehicle headlamps the reflecting surface used behind the light bulb is a concave mirror that produces a parallel beam of light that helps to see for long distances.

Light enters from air to glass having a refractive index 1 . 50 . What will be the speed of light in glass if the speed of light in air is 3 × 10 8 ms - 1 .

According to laws of refraction, if a light ray is entering from a rarer to denser medium it will bend towards the normal. The reason why light is bending towards the normal is the lower velocity of light in the denser medium when compared to the rarer medium. Here, light enters from air to glass having a refractive index 1 . 5 . We know the speed of light in a vacuum is 3 × 10 8 m s - 1 . Let us take the speed of light in a vacuum is c , speed of light in glass is v g , Refractive index of glass μ g = c v g ⇒ 1 . 5 = 3 × 10 8 v g ⇒ v g = 3 × 10 8 1 . 5 = 2 × 10 8 m s - 1