Identify the device used as a spherical mirror or lens in the following cases, when the image formed is virtual and erect in each case.
(i) Object is placed between device and its focus, image formed is enlarged and behind it.
(ii) Object is placed between the focus and device, image formed is enlarged and on the same side as that of the object.
(iii) Object is placed between infinity and device, image formed is diminished and between focus and optical centre on the same side as that of the object.
(iv) Object is placed between infinity and device, image formed is diminished and between pole and focus, behind it.
(i) Concave mirror
(ii) Convex lens
(iii) Concave lens
(iv) Convex mirror
Why does a light ray incident on a rectangular glass slab immersed in any medium emerge parallel to itself? Explain using a diagram.
The ray emerges parallel to itself because the lateral displacement produced during refraction at the first interface is compensated by the opposite displacement at the second interface. The emergent ray therefore becomes parallel to the incident ray.
A pencil when dipped in water in a glass tumbler appears to be bent at the interface of air and water. Will the pencil appear to be bent to the same extent if, instead of water, we use liquids like kerosene or turpentine? Support your answer with reason.
No, the pencil will not appear to bend to the same extent. The bending depends on the refractive index of the liquid. Since kerosene and turpentine have refractive indices different from water, the extent of bending will also differ.
How is the refractive index of a medium related to the speed of light? Obtain an expression for the refractive index of a medium with respect to another in terms of speed of light in these two media.
The refractive index of a medium is the ratio of the speed of light in vacuum to the speed of light in the medium: \( n = \dfrac{c}{v} \).
The refractive index of medium 2 with respect to medium 1 is given by: \( n_{21} = \dfrac{v_1}{v_2} \).
Refractive index of diamond with respect to glass is 1.6 and absolute refractive index of glass is 1.5. Find out the absolute refractive index of diamond.
Given: \( n_{dg} = 1.6 \) and \( n_g = 1.5 \).
The absolute refractive index of diamond is: \( n_d = n_{dg} \times n_g = 1.6 \times 1.5 = 2.40 \).
A convex lens of focal length 20 cm can produce a magnified virtual as well as real image. Is this a correct statement? If yes, where shall the object be placed in each case for obtaining these images?
Yes, the statement is correct.
A magnified virtual image is formed when the object is placed within 20 cm of the lens.
A magnified real image is formed when the object is placed between 20 cm and 40 cm from the lens.
Sudha finds that the sharp image of the window pane of her science laboratory is formed at a distance of 15 cm from the lens. She now tries to focus the building visible to her outside the window instead of the window pane without disturbing the lens. In which direction will she move the screen to obtain a sharp image of the building? What is the approximate focal length of this lens?
She should move the screen towards the lens to obtain a sharp image of the building.
The approximate focal length of the lens is 15 cm.
How are power and focal length of a lens related? You are provided with two lenses of focal length 20 cm and 40 cm respectively. Which lens will you use to obtain more convergent light?
Power of a lens is inversely proportional to focal length: \( P = \dfrac{1}{f} \).
The 20 cm focal length lens has greater power and will provide more convergent light.
Under what condition in an arrangement of two plane mirrors will the incident ray and reflected ray always be parallel to each other, whatever may be the angle of incidence? Show the same with the help of a diagram.
When two plane mirrors are placed at a right angle (90°) to each other, the incident and reflected rays always emerge parallel regardless of the angle of incidence.
Draw a ray diagram showing the path of rays of light when it enters with oblique incidence (i) from air into water; (ii) from water into air.
When light enters from air to water, it bends towards the normal. When light enters from water to air, it bends away from the normal, as shown in the standard ray diagrams.