Q1.
Power of the lens is – 4D, its focal length is :
(a) 4 m
(b) – 40 m
(c) – 0.25 m
(d) – 25 m
Q2.
The magnification produced by a spherical lens is +2.5. What is the nature of image and lens?
Q3.
An object is placed at a distance of 30 cm from a concave lens of focal length 30 cm. Determine the distance of the image from the lens. Also, find the magnification. What is the nature of the image obtained?
( v= –15 cm), (m = 0.5 )
Q5.
Define power of a lens. What is its unit? One student uses a lens of focal length 50 cm and another of –50 cm. What is the nature of the lens and its power used by each of them?
Q4.
The image of a candle flame formed by a lens is obtained on a screen placed on the other side of the lens. If the image is three times the size of the flame and the distance between lens and image is 80 cm, at what distance should the candle be placed from the lens? What is the nature of the image and the focal length of the lens?
( u= –80/3 cm ) ( f= 20 cm )
Q6.
If the image formed by a lens for all the positions of an object placed in front of it is always erect and diminished, what is the nature of the lens? Draw ray diagrams to justify your answer.
If the numerical value of the power of this lens is 10D, what is its focal length in SI units?
Q7.
At what distance should an object be placed from a convex lens of focal length 18 cm to obtain an image at 24 cm from it on the other side? What will be the magnification produced in this case?
( u= –72 cm ) ( m= –1/3 )
Q8.
We wish to obtain an equal size inverted image of a candle flame on a screen kept at a distance of 4 m from the candle flame.
(a) Name the type of lens that should be used.
(b) What should be the focal length of the lens and what distance from the lens the candle flame to be placed.
(c) Draw a labelled diagram to show the image formation in this case
Q9.
An object 4 cm high is placed at a distance of 10 cm from a convex lens of focal length 20 cm. Find the position, nature and size of the image.
( v= –20 cm), ( size = 8 cm )
Q10.
An object placed 4 cm in front of a converging lens produces a real image 12 cm from the lens. What is the magnification of the image? What is the focal length of the lens?
Also draw the ray diagram to show the formation of the image.
( f= 3 cm), ( m = –3 )
