Advertisements
Advertisements
Question
A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram.
Solution
Focal length f = −15 cm ...(negative due to sign convention)
Image distance v = −10 cm ...(negative due to sign convention)
Object distance u = ?
Applying the lens formula:
`1/"f" = 1/"v" - 1/"u"`
⇒ `1/"u" = 1/"v" - 1/"f"`
⇒ `1/"u" = 1/(-10) - 1/(-15)`
⇒ `1/"u" = -1/10 + 1/15`
⇒ `1/"u" = (-3 + 2)/30`
⇒ `1/"u" = (-1)/30`
u = − 30 cm
The object should be placed at a distance of 30 cm from the concave lens and on the left side.
APPEARS IN
RELATED QUESTIONS
Explain with the help of a diagram, why the concave lens is also called a diverging lens.
Define the principal focus of a concave lens.
List some things that concave lens and concave mirror have in common.
A converging lens is used to produce an image of an object on a screen,object on a screen. What change is needed for the image to be formed nearer to the lens?
(a) increase the focal length of the lens
(b) insert a diverging lens between the lens and the screen
(c) increase the distance of the object from the lens
(d) move the object closer to the lens
Things always look small on viewing through a lens. What is the nature of the lens?
When an object is placed 10 cm in front of lens A, the image is real, inverted, magnified and formed at a great distance. When the same object is placed 10 cm in front of lens B, the image formed is real, inverted and same size as the object.
What is the nature of lens B?
An object is placed at a distance of 4 cm from a concave lens of focal length 12 cm. Fine the position and nature of the image.
A concave lens has focal length 15 cm. At what distance should the object from the lens be placed so that it forms an image at 10 cm from the lens? Also find the magnification produced by the lens.
Calculate the image distance for an object of height 12 mm at a distance of 0.20 m from a concave lens of focal length 0.30 m, and state the nature and size of the image.
A person cannot see distant objects clearly. His vision can be corrected by using the spectacles containing:
(a) concave lenses
(b) plane lenses
(c) contact lenses
(d) convex lenses
Where will the image be formed if an object is kept in front of a concave lens at a distance equal to its focal length? Draw a ray diagram to illustrate your answer.
A lens forms an upright and diminished image of an object irrespective of its position. What kind of lens is this?
A student obtained clear image of window grills on the screen. But the teacher told him to get the image of a tree far away, instead of window. To get a clear image, the lens must be ............................
Express power of a concave lens of focal length 50 cm with its sign.
A lens forms an image between the object and the lens. Name the lens.
A concave lens has a focal length 30 cm. Find the position and magnification (m) of the image for an object placed in front of it at distance 30 cm. State whether the image is real or virtual?
An object is placed in front of a lens between its optical centre and focus. The formed image is virtual, erect, and diminished. Name the lens used.
