Lakhmir Singh Physics Class 10 Solutions Page No:206
Question 19: The shiny outer surface of a hollow sphere of aluminium of radius 50 cm is to be used as a mirror :
(a) What will be the focal length of this mirror ?
(b) Which type of spherical mirror will it provide ?
(c) State whether this spherical mirror will diverge or converge light rays.
Solution : (a) R = 50cm
f = ?
We know that
f = R/2 = 50/2 = 25 cm
(b) Convex mirror
(c) It will diverge light rays.
Question 20: What is the advantage of using a convex mirror as a rear-view mirror in vehicles as compared to a plane mirror ? Illustrate your answer with the help of labelled diagrams.
Solution : The advantage of using a convex mirror as a rear-view mirror in vehicles as compared to a plane mirror is that a convex mirror has a wider field of view as compared to a plane mirror. This enables driver to view much larger area of the traffic behind him.
Question 21: Give two uses of a convex mirror. Explain why you would choose convex mirror for these uses.
Solution : Two uses of convex mirror:
(i) A convex mirror is used as a rear-view mirror in vehicles because it forms erect and dimished images of the objects and has a wider field of view.
(ii) Big convex mirrors are used as security mirror in shops so that a large number of goods displayed in the shop can be seen in the convex mirror.
Question 22: What would your image look like if you stood dose to a large :
(a) convex mirror ?
(b) concave mirror ?
Solution : (a) Our image will be diminished, virtual and erect. This is because when the object lies anywhere between the pole and inifinity, the concave mirror forms a diminished, virtual and erect image.
(b) Our image will be enlarged, virtual and erect. This is because when the object lies within the focus of a concave mirror, it forms an enlarged, virtual and erect image.
Question 23: Which of the following are concave mirrors and which convex mirrors ?
Shaving mirrors, Car headlight mirror, Searchlight mirror, Driving mirror, Dentist’s inspection mirror, Torch mirror, Staircase mirror in a double-decker bus, Make-up mirror, Solar furnace mirror, Satellite TV dish, Shop security mirror.
Solution : Shaving mirror – concave mirror.
Car headlight mirror – concave mirror.
Searchlight mirror – concave mirror.
Driving mirror – convex mirror.
Dentist’s inspection mirror – concave mirror.
Torch mirror – concave mirror.
Staircase mirror in a double-decker bus – convex mirror.
Make-up mirror – concave mirror.
Solar furnace mirror – concave mirror.
Satellite TV dish – concave mirror.
Shop security mirror – convex mirror.
Question 24: How will you distinguish between a plane mirror, a concave mirror and a convex mirror without touching them ?
Solution : We can distinguish between a plane mirror, a concave mirror and a convex mirror by bringing our face close to each mirror, turn by turn. If the image is of the same size as our face, it is a plane mirror. If the image is magnified, it is a concave mirror. If the image is diminished, it is a convex mirror.
Question 25: If a driver has one convex and one plane rear-view mirror, how would the images in each mirror appear different ?
Solution : The images formed in the convex rear-view mirror will be smaller than those formed in the plane rear-view mirror.
Question 26: (a) Draw a labelled ray diagram to show the formation of image of an object by a convex mirror. Mark
clearly the pole, focus and centre of curvature on the diagram.
(b) What happens to the image when the object is moved away from the mirror gradually ?
(c) State three characteristics of the image formed by a convex mirror.
Solution : (a) Virtual and erect.
(b) Virtual and erect; real and inverted.