Advertisements
Advertisements
Question
A concave mirror forms a virtual image of size twice that of the object placed at a distance 5 cm from it.
Find : (a) the focal length of the mirror (b) position of image
Advertisements
Solution
m = `"I"/"O" = 20/"O" = 2`
∵ m = `-"v"/"u"`
∴ `-"v"/"u" = 2`
∴ -v = 2u
∵ u = -5 cm
∴ v = 10 cm
Hence , the position of the image is 10 cm behind the mirror.
From mirror formula ,
`1/"f" = 1/"v" + 1/"u"`
∴ `1/"f" = 1/10 + 1/(-5) = 1/10 - 1/5`
∴ f = -10 cm
APPEARS IN
RELATED QUESTIONS
One half of a convex lens of focal length 10 cm is covered with a black paper. Can such a lens produce an image of a complete object placed at a distance of 30 cm from the lens? Draw a ray diagram to justify your answer. A 4 cm tall object is placed perpendicular to its principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 15 cm. Find the nature, position and the size of the image.
Define the following term in the context of spherical mirrors:- Principal focus
Explain the following term related to spherical lenses:- aperture
Which type of mirror can form a real image?
A student obtained a sharp image of a burning candle, placed at the farther end of a laboratory table, on a screen using a concave mirror. For getting better value of focal length of the mirror, the subject teacher suggested him for focusing a well illuminated distant object. What should the student do?
(A) He should move the mirror away from the screen.
(B) He should move the mirror slightly towards the screen.
(C) He should move the mirror as well as the screen towards the newly selected object.
(D) He should move only the screen towards the newly selected object.
State the types of mirrors used for (i) headlights and (ii) rear view mirror, in cars and motorcycles. Give to justify your answer in each case.
What type of mirror can be used to obtain a real image of an object?
Select the correct option:
A concave mirror is made by cutting a portion of a hollow glass sphere of radius 30 cm. The focal length of the concave mirror is:
What is the focal length (f) of a mirror?
