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.
APPEARS IN
संबंधित प्रश्न
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.
A diverging lens has focal length of 3 cm. Calculate the power.
What is the nature of a lens having a power of + 0.5 D?
The optician's prescription for a spectacle lens is marked +0.5 D. What is the:
(a) nature of spectacle lens?
(b) focal length of spectacle lens?
How does focal length of a lens change when red light incident on it is replaced by violet light? Give reason for your answer.
A symmetric double convex lens is cut in two equal parts by a plane containing the principal axis. If the power of the original lens was 4 D, the power of a divided lens will be
A lens forms an upright and diminished image of an object, irrespective of its position. What kind of lens is this? Draw an outline ray diagram to show the formation of the image. State the position and one more characteristic of the image.
If focal length of a convex lens is 20 cm at what is the power of the lens?
An object is kept at a distance of 1m from a lens of power +2D:
- Identify the type of lens.
- Calculate its focal length and distance of the image formed.
In what unit is the power of a lens expressed?
