Advertisements
Advertisements
प्रश्न
A concave lens of 20 cm focal length forms an image 15 cm from the lens. Compute the object distance.
उत्तर
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
संबंधित प्रश्न
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
An object 2 cm tall stands on the principal axis of a converging lens of focal length 8 cm. Find the position, nature and size of the image formed if the object is:
(i) 12 cm from the lens
(ii) 6 cm from the lens
State one practical application each of the use of such a lens with the object in position (i) and (ii).
An object is placed 10 cm from a lens of focal length 5 cm. Draw the ray diagrams to show the formation of image if the lens is converging,
What type of lens is used to correct
myopia?
Complete the following sentence:
A short-sighted person cannot see ............ objects clearly. Short-sightedness can be corrected by using ........... lenses.
A concave lens forms a magnified or diminished image depending on the distance of an object from it.
At what distance from a concave lens of focal length 20 cm a 6 cm tall object be placed so as to obtain its image at 15 cm from the lens? Also calculate the size of the image formed.
Draw a ray diagram to justify your answer for the above situation and label it.
When an object is kept within the focus of a concave mirror, an enlarged image is formed behind the mirror. This image is :
State three characteristics of the image of an extended source, formed by a concave lens.
Convex magnifying glass is called divergent magnifying glass and concave magnifying glass is called converging magnifying glass.
