Advertisements
Advertisements
प्रश्न
An object of height 4 cm is placed at a distance of 15 cm in front of a concave lens of power, −10 dioptres. Find the size of the image.
उत्तर
Object distance u = -15 cm
Height of object h = 4 cm
Power of the lens p = -10 dioptres
Height of image h' = ?
Image distance v = ?
Focal length of the lens f = ?
We know that:
`p=1/f`
`f=1/p`
⇒`f=1/-10`
⇒ `f=-0.1m =-10 cm`
From the lens formula, we have:
`1/v-1/u=1/f`
`1/v-1/-15=1/-10`
⇒`1/v+1/15=-1/10`
⇒`1/v=-1/15-1/10`
⇒`1/v=(-2-3)/30`
⇒`1/v=-5/30`
⇒`1/v=-1/6`
⇒`v=-6` cm
Thus, the image will be formed at a distance of 6 cm and in front of the mirror.
Now, magnification m =`v/u=(h')/h`
or `(-6)/(-15)=(h')/4`
`h'=(6x4)/15`
`h'=24/15`
∴`h'=1.6 cm`
APPEARS IN
संबंधित प्रश्न
What does sign of power (+ve or –ve) indicate?
A student uses a lens of focal length 40 cm and another of –20 cm. Write the nature and power of each lens
The power of a lens is + 0.2 D. Calculate its focal length.
Fill in the following blank with suitable word:
For converging lenses, the power is __________ while for diverging lenses, the power is ___________.
The power of a combination of two lenses X and Y is 5 D. If the focal length of lens X be 15 cm :
(a) calculate the focal length of lens Y.
(b) state the nature of lens Y.
Two lenses A and B have focal lengths of +20 cm and, −10 cm, respectively.
(a) What is the nature of lens A and lens B?
(b) What is the power of lens A and lens B?
(c) What is the power of combination if lenses A and B are held close together?
State the condition for the following a lens has both its focal lengths equal .
A normal eye is not able to see objects closer than 25 cm because
A symmetric double convex lens in cut in two equal parts by a plane perpendicular to the principal axis. If the power of the original lens was 4 D, the power a cut-lens will be
A double convex lens has focal length 25 cm. The radius of curvature of one of the surfaces is double of the other. Find the radii, if the refractive index of the material of the lens is 1.5.
