(a) plane (b) concave (c) convex (d) either plane or convex Answer – The correct option is (d). The mirrors are likely to be either plane or convex. A virtual picture is formed by a plane mirror or...
A ray of light travelling in air enters obliquely into water. Does the light ray bends towards the normal or away from the normal? Why?
Answer- The light ray bends in the direction of normal. When a light ray passes through an optically rarer medium (low refractive index) and enters an optically denser medium (high refractive...
A student-focussed the image of a candle flame on a white screen using a convex lens. He noted down the position of the candle screen and the lens as under
Position of candle = 12.0 cm Position of convex lens = 50.0 cm Position of the screen = 88.0 cm What is the focal length of the convex lens?Where will the image be formed if he shifts the candle...
Define power of a lens. What is its unit? One student uses a lens of focal length 50 cm and another of –50 cm. What is the nature of the lens and its power used by each of them?
Power of lens Is the degree of convergence and divergence provided by a lens and its unit is Diopter (D). The focal length of the lens used by the first student is in positive so it is a convex...
Size of the image of an object by a mirror having a focal length of 20 cm is observed to be reduced to 1/3rd of its size. At what distance the object has been placed from the mirror? What is the nature of the image and the mirror?
Given, m = 1/3 Using = 1/v+1/u=1/f Calculating u, u = – 80 cm. The image is real and inverted so the mirror is concave.
The image of a candle flame formed by a lens is obtained on a screen placed on the other side of the lens. If the image is three times the size of the flame and the distance between the lens and image is 80 cm, at what distance should the candle be placed from the lens? What is the nature of the image at a distance of 80 cm and the lens?
Ray Diagram The image in the screen is real and so, the magnification is, m = –3 v = 80 cm u = ? m = v/u –3 = 80/u u = –80/3 cm As we know, 1/f = 1/v – 1/u =1/80 + 3/80 = 4/80 =...
Draw ray diagrams showing the image formation by a convex mirror when an object is placed
(a) at infinity (b) at a finite distance from the mirror (a) (b)
Draw ray diagrams showing the image formation by a concave lens when an object is placed
(a) at the focus of the lens (b) between focus and twice the focal length of the lens (c) beyond twice the focal length of the lens (a) (b) (c)
Write laws of refraction. Explain the same with the help of a ray diagram, when a ray of light passes through a rectangular glass slab.
The Laws of refraction: The Incident ray, refracted ray and the normal at the point of incidence lies in the same plane. The ratio of the sine of incidence and sine of refraction is same for the...
Draw ray diagrams showing the image formation by a convex lens when an object is placed
(a) between optical centre and focus of the lens (b) between focus and twice the focal length of the lens (c) at twice the focal length of the lens (d) at infinity (e) at the focus of the lens (a)...
Draw ray diagrams showing the image formation by a concave mirror when an object is placed
(a) between pole and focus of the mirror (b) between focus and centre of curvature of the mirror (c) at the centre of curvature of the mirror (d) a little beyond the centre of curvature of the...
Draw a ray diagram showing the path of rays of light when it enters with oblique incidence
1. From air into water; 2. From water into air. 1. 2.
Under what condition in an arrangement of two plane mirrors, incident ray and reflected ray will 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 perpendicular to each other, then the Incident ray and the reflected ray will always be parallel to each other.
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?
The power of lens is inversely proportional to the focal length of the lens and the lens with focal length 20 has more power when compared to a lens with a focal length of 40 cm. The lens having...
Refractive index of diamond with respect to glass is 1.6 and the absolute refractive index of glass is 1.5. Find out the absolute refractive index of diamond.
Given, Absolute RI of diamond= 1.6 Absolute RI of glass= 1.5 Thus, Absolute refractive index of diamond = 2.4
Sudha finds out 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?
To get a clear picture of the structure, Sudha has to move the screen and remove the lens. The length of the area will be about 15 cm. The light rays from a distant object such as a tree or a...
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?
When an object is in F and F2 of a convex lens. So, we need to place the object between 20 and 40 cm of the lens. When an object is placed between F and 0 of a convex lens, its magnified, vertical...
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 can be seen as a factor in reducing the speed and length of radiation in relation to vacuum values. w = civ where, n- Refractive index c – Speed of light v- Velocity The ratio...
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.
The bending of light here is a reversal function. Reversal is based on refractive indices. The opposing indices of paraffin or turpentine will not be the same as water. So the degree of bending will...
Why does a light ray incident on a rectangular glass slab immersed in any medium emerges parallel to itself? Explain using a diagram.
When light ray penetrates into the denser medium from the abnormal bend to the normal In this case the magnitude of the curvature of the parallel radiation is the same. Thus, the emergent ray is...
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.
1. Object is placed between the device and its focus, an image formed is enlarged and behind it. 2. Object is placed between the focus and device, an image formed is enlarged and on the same side as...
In which of the following, the image of an object placed at infinity will be highly diminished and point sized?
(a) Concave mirror only (b) Convex mirror only (c) Convex lens only (d) Concave mirror, convex mirror, concave lens and convex lens Answer: (d) Concave mirror, convex mirror, concave lens and convex...
A child is standing in front of a magic mirror. She finds the image of her head bigger, the middle portion of her body of the same size and that of the legs smaller. The following is the order of combinations for the magic mirror from the top.
(a) Plane, convex and concave (b) Convex, concave and plane (c) Concave, plane and convex (d) Convex, plane and concave Answer: (c) Concave, plane and convex Explanation: Concave mirror showed her...
You are given water, mustard oil, glycerine and kerosene. In which of these media a ray of light incident obliquely at same angle would bend the most?
(a) Kerosene (b) Water (c) Mustard oil (d) Glycerine Answer: (d) Glycerine Explanation: A ray of light incident obliquely at same angle would bend the most in glycerine media.
Which of the following ray diagrams is correct for the ray of light incident on a concave mirror as shown in the figure?
LRR PIC 6----- (a) Fig. A (b) Fig. B (c) Fig. C (d) Fig. D Answer: (d) Fig. D Explanation: The ray diagram in Figure D is correct for the ray of light incident on a concave mirror as the incident is...
The laws of reflection hold good for
(a) plane mirror only (b) concave mirror only (c) convex mirror only (d) all mirrors irrespective of their shape Answer: (d) all mirrors irrespective of their shape Explanation: The laws of...
In torches, searchlights and headlights of vehicles the bulb is placed
(a) between the pole and the focus of the reflector (b) very near to the focus of the reflector (c) between the focus and centre of curvature of the reflector (d) at the centre of curvature of the...
A full-length image of a distant tall building can definitely be seen by using
(a) a concave mirror (b) a convex mirror (c) a plane mirror (d) both concave as well as plane mirror Answer: (b) a convex mirror Explanation: A full-length image of a distant tall building can...
Rays from Sun converge at a point 15 cm in front of a concave mirror. Where an object should be placed so that size of its image is equal to the size of the object?
(a) 15 cm in front of the mirror (b) 30 cm in front of the mirror (c) between 15 cm and 30 cm in front of the mirror (d) more than 30 cm in front of the mirror Answer: (d) more than 30 cm in front...
Magnification produced by a rearview mirror fitted in vehicles
(a) is less than one (b) is more than one (c) is equal to one (d) can be more than or less than one depending upon the position of the object in front of it Answer: (a) is less than one Explanation:...
Which of the following statements is true?
(a) A convex lens has 4 dioptre power having a focal length 0.25 m (b) A convex lens has –4 dioptre power having a focal length 0.25 m (c) A concave lens has 4 dioptre power having a focal length...
Beams of light are incident through the holes A and B and emerge out of the box through the holes C and D respectively as shown in the Figure. Which of the following could be inside the box?
(a) A rectangular glass slab (b) A convex lens (c) A concave lens (d) A prism Answer: (a) A rectangular glass slab Explanation: When the beams of light are incident through the holes A and B and...
A light ray enters from medium A to medium B as shown in the Figure. The refractive
index of medium B relative to A will be (a) greater than unity (b) less than unity (c) equal to unity (d) zero Answer: (a) greater than unity Explanation: The refractive index is the bending of a...
The figure shows a ray of light as it travels from medium A to medium B. Refractive index of the
medium B relative to medium A is (a) √3 / √2 (b) 2 / 3 (c) 1/ 2 (d) 2 Answer: (a) √3 / √2 Explanation: According to the Snell’s law, the refractive index of the medium B relative to the medium A is...
Which of the following can make a parallel beam of light when light from a point source is incident on it?
(a) Concave mirror as well as convex lens (b) Convex mirror as well as a concave lens (c) Two plane mirrors placed at 90° to each other (d) Concave mirror as well as a concave lens Answer: (d)...