Question

What type of mirror is used to obtain a ‘ real image’?

(a) What do you understand by the term ‘ virtual image’?

(b) Name two type of mirror which always form a virtual image.

(c) Is the virtual image always erect ?

Prove that for a concave mirror , the radius of curvature is twice its focal length.
What is the minimum number of rays required for locating the image formed by a concave mirror for an object ?

Draw a ray diagram to show the formation of image by a concave mirror.

Draw a ray diagram to show the
(a) position and.
(b) nature of the image formed when object is placed between focus F and pole P of a concave mirror.​

Answer 1

Answer:

1. Concave mirror is used to obtain a ‘ real image’.
2. An image which is formed when two or more reflected rays appear to intersect at a point behind a mirror is known as virtual image.
3. Plane mirror and Convex mirror always form a virtual image.
4. Yes, virtual image is always erect.
5. To show that f = R/2

Let a ray of light AB incident parallel

to principal of axis on a concave

mirror.Afte reflection, the ray AB

passes along BD, through the

focus. BC is normal to the concave

mirror at B.

/_ABC = /_CBD ( i ) [according to

law of reflection]

we know that AB & PC are parallel

to each other.

/_ABC = /_BCP ( ii ) [alternate

angle]

From equations i and ii

/_CBD = /_BCP

Hence triangle BCF is isosceles

BF = CF ( iii )

If the aperture of the mirror is small

than B will be very close to P.

BF = PF ( iv )

From equation iii and iv

CF = PF = 1/2PC

By definition PF = focal length & PC

= radius of curvature

Hence f = R/2

At least two rays required for

locating the image formed by a

concave mirror for an object.

6. In the above picture.

7. In the above picture.

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