Advertisements
Advertisements
प्रश्न
An object of height 4.25 mm is placed at a distance of 10 cm from a convex lens of power +5D. Find (i) the focal length of the lens, and (ii) the size of the image.
Advertisements
उत्तर
Object height, h = 4.25 mm = 0.425 cm (1 cm = 10 mm)
Object distance, u =-10 cm
Power, P = +5 D
Focal length, f = ?
Image distance, v = ?
Image height, h' = ?
Power, P `=1/f`
`f=1/p=1/5=0.2m =20cm `
Using the lens formula, we get:
`1/v-1/u=1/f`
`1/v-1/-10=1/20`
`1/v+1/10=1/20`
`1/v=1/20-1/10`
`1/v=-1/20`
∴ v=-20cm
Now, magnification, m = `(h')/h=v/u`
Substituting the values in the above equation, we get:
`(h')/0.425=(-20)/-10`
`h'=2X0.425=0.85cm=8.5mm`
Thus, the image is 8.5 mm long; it is also erect and virtual.
APPEARS IN
संबंधित प्रश्न
What is the power of a convex lens of focal length 0.5 m?
A diverging lens has focal length of 3 cm. Calculate the power.
What is the nature of a lens whose power is, −4 D?
A lens has a focal length of, −10 cm. What is the power of the lens and what is its nature?
Fill in the following blank with suitable word:
For converging lenses, the power is __________ while for diverging lenses, the power is ___________.
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.
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.
A combination of lenses for a camera contains two converging lenses of focal lengths 20 cm and 40 cm and a diverging lens of focal length 50 cm. Find the power and focal length of the combination.A optical instrument in which the above arrangement of convex lens is used is a convex lens used to burn paper by focusing sunlight.
The power of a lens is +2.0D. Its focal length should be :
Express the power (with sign) of a concave lens of focal length 20 cm.
A normal eye is not able to see objects closer than 25 cm because
Consider three converging lenses L1, L2 and L3 having identical geometrical construction. The index of refraction of L1 and L2 are \[\mu_1 \text{ and } \mu_2\] respectively. The upper half of the lens L3 has a refractive index \[\mu_1\] and the lower half has \[\mu_2\] following figure . A point object O is imaged at O1 by the lens L1 and at O2 by the lens L2placed in same position. If L3 is placed at the same place,
(a) there will be an image at O1
(b) there will be an image at O2.
(c) the only image will form somewhere between O1 and O2
(d) the only image will form away from O2.
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.
How is accommodation produced?
The following diagram shows the object O and the image I formed by a lens. Copy the diagram and on it mark the positions of the lens LL’ and focus (F). Name the lens.
If the lens is of focal length 25 cm. Calculate the power of the lens.
Power of a lens is – 4D, then its focal length is
A point object is placed at O in front of a glass sphere as shown in figure.
Show the formation of the image by the sphere.
