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
State the power of a lens S.I. unit.
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
What is the nature of a lens whose power is, −4 D?
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 ___________.
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.
What do you understand by the power of a lens?
What is the unit of power of a lens? Define the unit of power of a lens.
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.
Mohan obtained a sharp inverted image of a distant tree on the screen placed behind the lens. He then moved the screen and tried to look through the lens in the direction of the object. He would see:
(1) a blurred image on the wall of the laboratory.
(2) an erect image of the tree on the lens.
(3) no image as the screen has been removed
(4) an inverted image of the tree at the focus of the lens.
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 convex lens produces a double size real image when an object is placed at a distance of 18 cm from it. Where should the object be placed to produce a triple size real image?
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.
Complete the diagram to show the formation of the image of the object AB.
(i) Name the Lens LL’.
(ii) Where is the image of the object AB formed?
(iii) State three characteristics of the image.
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.
The power of lens depends on the focal length of the lens
Increase in the converging power of eye lens cause ‘hypermetropia'
The deviation of the incident light rays produced by a lens on refraction through it is a measure of its:
A convex lens is a converging lens whose focal length and power are both:
When a lens is placed in a liquid, the total power of the lens is:
If the refractive index of the lens material is less than that of the surrounding liquid (\[n_2 < n_1\]), then:
