Chapter 6 - Light - Spherical Mirrors Exercise 258
What do you mean by a spherical mirror?
A spherical mirror is a part of a hollow glass sphere silvered on one side.
Explain with a suitable diagram, the converging of a parallel beam of light rays by a concave mirror.
If the radius of curvature of a concave mirror is 30 cm, what is its focal length?
Focal length = 1/2 of radius of curvature
= 1/2 X 30 = 15cm.
What do you mean by a focal point?
Focal point is the principal focus of the mirror where a parallel beam of light meets(or appear to meet) after reflection from the mirror.
Distinguish between real and virtual images.
Define the terms;
(ii) Centre of curvature
(iv) Principal axis
(v) Principal focus
(i). Pole is the centre of the reflecting surface, in this case spherical mirror.
(ii). Centre of curvature is the centre of the imaginary sphere to which the mirror belongs
(iii). Aperture is the distance between the extreme points on the periphery of the mirror.
(iv). Principal axis is the straight line passing through the pole and the centre of curvature.
(v) The principle focus of a spherical mirror may be defined as a point on its principle axis where a beam of light parallel to the principle axis converges to or appears to diverge from after reflection from the spherical mirror.
Which mirror has a wider field of view?
Convex mirror has a wider field of view.
Give three applications of concave mirrors.
Concave mirrors are used in reflecting microscope, in shaving and make up glasses and in ophthalmoscope.
Mention one main application of convex mirrors.
Convex mirrors are used as a rear view mirror in automobiles as it provides a wider view of following traffic.
What kind of mirror is used in vehicles to see the traffic following it?
Convex mirror is used in vehicles to see the traffic following it.
For what position of an object, a concave mirror forms a real image equal in size to the object?
For what position of an object, a concave mirror forms an enlarged virtual image?
Name the spherical mirror which can produce a real and diminished image of the object.
Concave mirror can produce real and diminished image of the object.
What is the focal length of a plane mirror?
The focal length of plane mirror is infinity.
Where should an object be placed in front of a concave mirror so as obtain its magnified erect image?
The object should be placed between F and P to obtain its magnified and erect image.
How will you determine the focal length of a concave mirror?
What do you mean by the magnification produced by mirrors?
Linear magnification is defined as the ratio of the height of the image to the height of the object. It is taken to be positive for an image to be virtual and erect and negative when image is real and inverted.
Magnification = height of image / height of object.
Write down the SI unit of focal length.
SI unit of focal length is meter.
A person in front of a spherical mirror finds his image having a very small head, a fat body and legs of normal size. What are the shapes of three parts of the mirror?
The top mirror is convex mirror, the middle mirror is concave mirror and bottom mirror is a plane mirror.
What is the nature of a mirror having a focal length of +15 cm?
The mirror having +15 cm as its focal length is a convex mirror because focal length is taken positive only in case of convex mirror.
What is the nature of the mirror having a focal length of -20 cm?
The mirror having -20 cm as its focal length is a concave mirror because focal length is taken negative only in case of concave mirror.
When we look into a plane mirror, is the image of our face real or virtual?
When we look into a plane mirror, the image of our face is virtual because the image cannot be obtained on a screen.
An object is brought towards a concave mirror. How does the position and size of the image change?
When an object is brought towards the concave mirror, the position of the image moves away from the mirror and the size increases and it remains inverted but at object position between F and P, the image is virtual, magnified and erect.