Advertisements
Advertisements
Question
A concave lens of 20 cm focal length forms an image 15 cm from the lens. Compute the object distance.
Solution
Focal length of concave lens f = - 20 cm (focal length is negative for a concave lens)
Image distance v = - 15 cm ( negative sign is given because the image formed by a concave lens is on the left side of the lens)
Using the lens formula:
`1/f=1/v-1/u`
`1/-20=1/-15-1/u`
`1/u=1/20+1/((-15)`
`1/u=(3-4)/60=-1/60`
∴ u=-60 cm.
The negative sign shows that the object is on the left side of the concave lens.
Therefore, the object is at a distance of 60 cm and on the left side of the concave lens.
APPEARS IN
RELATED QUESTIONS
A ray of light is going towards the focus of a concave lens. draw a ray diagram to show the path of this ray of light after refraction through the lens.
Which type of lens is :
a converging lens, and which is
Construct ray diagrams to illustrate the formation of a virtual image using a converging lens,
A beam of light is incident through the holes on one side of a box and emerges out through the holes on its opposite side as shown in the following figure:
The box contains:
(a) a glass prism
(b) a concave lens
(c) a convex lens
(d) a parallel-sided glass slab
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.
An object is 2 m from a lens which forms an erect image one-fourth (exactly) the size of the object. Determine the focal length of the lens. What type of lens is this?
Name one of the common defects of vision and the type of lens used to remove it.
Complete the following sentence:
A short-sighted person cannot see ............ objects clearly. Short-sightedness can be corrected by using ........... lenses.
An object is placed on the axis of a lens. An image is formed by refraction in the lens. For all positions of the object on the axis of the lens, the positions of the image are always always between the lens and the object name the lens.
Draw images in case of a concave lens when the object is at infinity.
