Advertisements
Advertisements
प्रश्न
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.A optical instrument in which the above arrangement of convex lens is used is a convex lens used to burn paper by focusing sunlight.
Advertisements
उत्तर
Focal length (f1) of the 1st converging lens = 20 cm = 0.2 m
Focal length (f2) of the 2nd converging lens = 40 cm = 0.4 m
Focal length (f3) of the diverging lens = -50 cm = -0.5 m (negative sign due to sign convention)
Power = `1/"foccal length of lens (in metre)"`
Power (P1) of 1st lens = `1/0.2=2.5D`
power (P2) of 2nd lens = `1/0.4=2.5 D`
Power (P3) of diverging lens =`1/0.5 =-2D`
Net power of the combination = P1 + P2+ P3 = 5 + 2.5 + (-2) = 5.5 D
Net focal length of the combination = `1/"net power"=1/5.5=0.1818m=18.18 cm`
APPEARS IN
संबंधित प्रश्न
Define the power of a lens.
Find the focal length of a lens of power −2.0 D. What type of lens is this?
What can you see in a completely dark room? If you switch on an electric bulb in this dark room as a light source, explain how you could now see:
(a) the electric bulb
(b) a piece of white paper
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:
Give the usual name for the following:
A point inside a lens through which the light passes undeviated.
Which type of lens has (a) a positive power, and (b) a negative power?
What is the power of a convex lens of focal length 0.5 m?
What is the nature of a lens whose power is, −4 D?
Fill in the following blank with suitable word:
For converging lenses, the power is __________ while for diverging lenses, the power is ___________.
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.
A 5.0 diopter lens forms a virtual image which is 4 times the object placed perpendicularly on the principal axis of the lens. Find the distance of the object from the lens.
The power of the magnifying glass depends on the distance of the magnifying glass from object.
According to Rayleigh’s scattering law, the amount of scattering of light is inversely proportional to the fourth power of its ______.
Assertion and reasoning type
- Assertion: Myopia is due to the increase in the converging power of eye lens.
- Reason: Myopia can be corrected with the help of concave lens.
The focal length of a concave lens is 20 cm. The focal length of a convex lens is 25 cm. These two are placed in contact with each other. What is the power of the combination? Is it diverging, converging or undeviating in nature?
When monochromatic red light is used instead of blue light in a convex lens, its focal length will ______.
In what unit is the power of a lens expressed?
