Important Questions For Practice
1. With the help of ray diagram explain the phenomenon of total internal reflection. Obtain the relation between critical angle and refractive indices of two media. Draw ray diagram to show how right angled isosceles prism can be used to: (i) Deviate the ray through 180┬░. (ii) Deviate the ray through 90┬░.
(iii) Invert the ray.
2. The refractive index of medium is 1.5. A beam of light of wavelength 6000 A┬░ enters in the medium from air. Find wavelength and frequency of light in the medium.
3. An object of length 2.5cm is placed at a distance of 1.5f from a concave mirror where f is the focal length of the mirror. The length of object is perpendicular to principal axis. Find the size of image. Is the image erect or inverted?
4. For a man shortest distance of distinct vision is 20 cm. What will be the type and power of lens which would enable him to read a book at a distance of 60 cm?
5. A hypermetropic person whose near point is at 100 cm wants to read a book. Find the nature and power of the lens needed.
Questions From Board Papers
1. A near sighted person can clearly see objects up to a distance of 1.5m. Calculate power of the concave lens of focal length 1.5 m for the remedy of this defect. (P = тАУ 0.67D)
2. Two poles-one 4m high and the other is 4.5 m high are situated at distance 40m and 50m respectively from an eye. Which pole will appear taller?
3. The angle subtended at the eye by an object is equal to the angle subtended at the eye by the virtual image produced by a magnifying glass. In what sense then does magnifying glass produce angular magnification?
4. You are provided with four convex lenses of focal length 1cm, 3cm, 10cm and 100 cm. Which two would you prefer for a microscope and which two for a telescope.
5. A microscope is focussed on a dot at the bottom of the beaker. Some oil is poured into the beaker to a height of тАШbтАЩ cm and it is found that microscope has to raise through vertical distance of тАШaтАЩ cm to bring the dot again into focus. Express refractive index of oil is terms of a and b.
Important Questions On 12th Physics Chapter 9
Plane and convex mirrors can produce real images as well. If the object is virtual,
i.e., if the light rays converging at a point behind a plane mirror (or a convex mirror) are reflected to a point on a screen placed in front of the mirror, then a real image will be formed.
A virtual image is formed when light rays diverge. The convex lens of the eye causes these divergent rays to converge at the retina. In this case, the virtual image serves as an object for the lens to produce a real image.
The apparent depth of a tank of water changes when viewed obliquely. This is because light bends on travelling from one medium to another. The apparent depth of the tank when viewed obliquely is less than the near-normal viewing.
The refractive index of diamond (2.42) is more than that of ordinary glass (1.5). The critical angle for diamond is less than that for glass. A diamond cutter uses a large angle of incidence to ensure that the light entering the diamond is totally reflected from its faces. This is the reason for the sparkling effect of a diamond.
The best position of the eye for viewing through a compound microscope is at the eye-ring attached to the eyepiece. The precise location of the eye depends on the separation between the objective lens and the eyepiece.