Advertisements
Advertisements
प्रश्न
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.
Advertisements
उत्तर
(a) The focal length of lens X, ie., f1 = 15 cm = 0.15 m
Power of lens X, `p_-1=1/f_1=1/0.15=6.67` D
Let the power and the focal length of the lens Y be P2 and f2, respectively.
The resultant power of the combination of two lenses is the algebraic sum of the powers of the individual lenses.
∴ Power of combination of lenses P = P1 + P2
⇒5 = 6.67 + P2
⇒P2 = 5 - 6.67 = - 1.67 D
The power of the lens is related to the focal length of the lens as:
`p_2=1/f_2`
`-1.67=1/f_2`
`f_2=1/-1.67=0.60`m=-60cm
`f_2=1/-1.67=-0.60m=-60cm`
The focal length of the lens Y is -60 cm.
(b) The focal length of the lens Y is negative. Therefore, the lens is concave and diverging in nature.
APPEARS IN
संबंधित प्रश्न
Calculate the focal length of a corrective lens having power +2.5 D.
(a) At what distance should the lens be held from the figure in order to view the squares distinctly with the maximum possible magnifying power?
(b) What is the magnification in this case?
(c) Is the magnification equal to the magnifying power in this case? Explain.
You have two lenses A and B of focal lengths +10 cm and –10 cm, respectively. State the nature and power of each lens. Which of the two lenses will form a virtual and magnified image of an object placed 8 cm from the lens? Draw a ray diagram to justify your answer
Consider two statements A and B given below:
A: real image is always inverted
B: virtual image is always erect
Out of these two statements:
The lens A has a focal length of 25 cm whereas another lens B has a focal length of 60 cm. Giving reason state, which lens has more power: A or B.
The focal length of a convex lens is 25 cm. What is its power?
What is the nature of a lens whose power is, −4 D?
The focal length of a lens is +150 mm. What kind of lens is it and what is its power?
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.
Express the power (with sign) of a concave lens of focal length 20 cm.
A double convex lens has two surfaces of equal radii R and refractive index \[m = 1 \cdot 5\]
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 pin of length 2.00 cm is placed perpendicular to the principal axis of a converging lens. An inverted image of size 1.00 cm is formed at a distance of 40.0 cm from the pin. Find the focal length of the lens and its distance from the pin.
How is accommodation produced?
A stick partly immersed in water appears to be bent. Draw a ray diagram to show the bending of the stick when placed in water and viewed obliquely from above.
Power of a lens is – 4D, then its focal length is
According to Rayleigh’s scattering law, the amount of scattering of light is inversely proportional to the fourth power of its ______.
The power of lens depends on the focal length of the lens
