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
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.
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.
How is the power of a lens related to its focal length?
A converging lens has focal length of 50 mm. What is the power of the lens?
A diverging lens has focal length of 3 cm. Calculate the power.
The power of a lens is + 0.2 D. Calculate its focal length.
The power of a lens is, −2 D. What is its focal length?
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 words :
The reciprocal of the focal length in metres gives you the _________ of the lens, which is measured in ___________.
Fill in the following blank with suitable word:
For converging lenses, the power is __________ while for diverging lenses, the power is ___________.
A convex lens of focal length 25 cm and a concave lens of focal length 10 cm are placed in close contact with one another.
(a) What is the power of this combination?
(b) What is the focal length of this combination?
(c) Is this combination converging or diverging?
What do you understand by the power of a lens? Name one factor on which the power of a lens depends.
A diverging lens has a focal length of 0.10 m. The power of this lens will be:
State the condition for the following a ray passes undeviated through the lens .
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 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.
Surabhi from std. X uses spectacle. The power of the lenses in her spectacle is 0.5 D.
Answer the following questions from the given information:
- Identify the type of lenses used in her spectacle.
- Identify the defect of vision Surabhi is suffering from.
- Find the focal length of the lenses used in her spectacle.
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.
The power of lens depends on the focal length of the lens
