Advertisements
Advertisements
प्रश्न
If there is a convex lens of focal length 75 cm and a concave lens of focal length 40 cm, then calculate their combined power and combined focal length.
Advertisements
उत्तर
Power of convex lens = `100/("f"("cm"))`
= `100/75` = + 1.33 D.
Power of concave lens = `100/("f"("cm"))`
= `100/40` = − 2.5 D.
Their combined power P = + 1.33 D + (− 2.5 D)
P = − 1.17 D.
Their combined focal length F = `100/"P"=100/(-1.17)`
F = − 85.47 cm.
Negative sign indicates that the nature of their combination is concave.
संबंधित प्रश्न
What is the focal length of a convex lens of focal length 30 cm in contact with a concave lens of focal length 20 cm? Is the system a converging or a diverging lens? Ignore thickness of the lenses.
Ranbir claims to have obtained an image twice the size of the object with a concave lens. Is he correct? Give a reason for your answer.
Give the usual name for the following:
A point inside a lens through which the light passes undeviated.
What is the power of a convex lens lens whose focal length is 80 cm?
What is the nature of a lens having a power of + 0.5 D?
What is the nature of a lens whose power is, −4 D?
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.
Define power of a lens. What is its unit? One student uses a lens of focal length 50 cm and another of –50 cm. What is the nature of the lens and its power used by each of them?
The focal length of a double convex lens is equal to the radius of curvature of either surface. What is the refractive index of its material?
