Advertisements
Advertisements
Question
An object of height 5 cm is placed perpendicular to the principal axis of a concave lens of focal length 10 cm. If the distance of the object from the optical centre of the lens is 20 cm, determine the position, nature and size of the image formed using the lens formula.
Solution
Given:-
Height of the object = h = 5 cm
Focal length of the concave lens = f = −10 cm
Object distance = u = −20 cm
Using the lens formula, we get
`1/"f"=1/"v"-1/"u"`
`therefore1/"v"=1/"f"+1/"u"=1/(-10)-1/20=(-2-1)/20=(-3)/20`
`therefore"v"=-6.67cm`
Hence, the image is formed 6.67 cm in front of the lens on the same side as the object.
Because v is negative, we can say that the image is virtual.
From the magnification formula for the lens, we get
`"m"=(h')/h="v"/"u"`
`thereforeh'="vh"/"u"=(-6.67xx5)/-20=1.67cm`
Hence, the size of the image is h′ = 1.67 cm.
Because the height of the image is positive and smaller than the height of the object, the image is erect and diminished.
So, we can conclude that the image is virtual, erect and diminished.
RELATED QUESTIONS
To determine the approximate value of the focal length of a given concave mirror, you focus the image of a distant object formed by the mirror on a screen. The image obtained on the serene, as compared to the object is always:
(a) Laterally inverted and diminished
(b) Inverted and diminished
(c) Erect and diminished
(d) Erect and highly diminished
A student obtained a sharp image of a candle flame placed at the distant end of the laboratory table on a screen using a concave mirror to determine its focal length. The teacher suggested him to focus a distant building, about 1 km away from the laboratory, for getting more correct value of the focal length. In order to focus the distant building on the same screen, the student should slightly move the
(a) mirror away from the screen
(b) screen away from the mirror
(c) screen towards the mirror
(d) screen towards the building
Study the following diagram and select the correct statement about the device 'X' :
(A) Device 'X' is a concave mirror of radius of curvature 12 cm
(B) Device 'X' is a concave mirror of focal length 6 cm
(C) Device 'X' is a concave mirror of focal length 12 cm
(D) Device 'X' is a convex of mirror of focal length 12 cm
An object is placed at a distance of 10 cm from a concave mirror of focal length 20 cm.
Calculate the image distance.
What type of mirror should be used as a shaving mirror?
Which of the following are concave mirrors and which convex mirrors?
Shaving mirrors, Car headlight mirror, Searchlight mirror, Driving mirror, Dentist's inspection mirror, Touch mirror, Staircase mirror in a double-decker bus, Make-up mirror, Solar furnace mirror, Satellite TV dish, Shop security mirror.
Which of the following can make a parallel beam of light from a bulb falls on it?
(a) concave mirror as well as concave lens
(b) convex mirror as well as concave lens
(c) concave mirror as well as convex lens
(d) concave mirror as well as convex lens
Draw a ray diagram to show the formation of image of an object placed at the centre of curvature of a concave mirror. State the position, size and nature of the image.
An erect and enlarged image can be formed by
To obtain an image twice the size of the object, between which two points related to a concave mirror should an object be placed?
