Home
Class 12
PHYSICS
A point source of light is placed 60 cm ...

A point source of light is placed 60 cm away from screen. Intensity detected at point P is `I` . Now a diverging lens of focal length 20cm is placed 20cm away from S between S and P. The lens transmits `75%` of light incident on it. Find the new value intensity at P.

Text Solution

Verified by Experts

`u=-20,f=-20rArrv=-10`
Let P=Power of source
`I=(P)/(4pi(60)^(2))`
Energy receibed by lens,
`E_(2)=(P)/(4pi(20)^2)A_1`
`:. I_(2)=(0.75E_(2))/(A_(2))`
From similar triangles `(A_(2))/(A_(1))=25`
`:. I_(2)=0.27I`
Promotional Banner

Topper's Solved these Questions

  • GEOMETRICAL OPTICS

    CENGAGE PHYSICS ENGLISH|Exercise Solved Examples|15 Videos

  • GEOMETRICAL OPTICS

    CENGAGE PHYSICS ENGLISH|Exercise Exercise1.1|14 Videos

  • ELECTRON,PHONTS,PHOTOELECTRIC EFFECT & X-RAYS

    CENGAGE PHYSICS ENGLISH|Exercise dpp 3.3|15 Videos

  • HEATING EFFECT OF CURRENT

    CENGAGE PHYSICS ENGLISH|Exercise Thermal Power in Resistance Connected in Circuit|27 Videos

Similar Questions

Explore conceptually related problems

Two converging lenses of focal lengths f_(1)=10cm and f_(2)=20cm are placed at some separation. A parallel beam of light is incident on first lens. Then,

A point source of light is placed at a distance of 2f from a converging lens of focal length f. The intensity onteh other side of the lens is maximum at a distance

A point source of light S is placed on the axis of a lens of focal length 20cm at a distance 25cm from lense. A screen is placed normal to the axis of lens at a distance x from it (treat all rays as paraxial). Identify the true or false statements. a. As x is increased from zero , intensity continuously decreases. b. As x is increased from zero, intensity first increases then decreases. c. Intensity at center of screen for x =90 cm and x=110 cm is same.

A convex lens of focal length 20cm is placed 10cm away from a second convex lens of focal length 25 cm. What wil be the location of the image of an object at 30 cm in front of the first lens?

Find distanace of image from a convex lens of focal length 20cm if object is placed at a distance of 30cm from the lens. Also find its magnification.

A point source S is placed at a distance of 15 cm from a converging lens of focal length 10 cm on its principal axis. Where should a diverging miror of focal length 12 cm be placed to that a real image is formed on the source itself.

In displacement method distance of object from convex lens of focal length 20 cm in one position 60 cm. Then

When an object is placed 40cm from a diverging lens, its virtual image is formed 20cm from the lens. The focal length and power of lens are

A diverging lens of focal length 10cm is placed 10cm in front of a plane mirror as shown in Fig. Light from a very far away source falls on the lens. What is the distance of final image?

A point source of light is 60 cm from a screen and is kept at the focus of a concave mirror which reflects light on the screen. The focal length of the mirror is 20 cm. The ratio of average intensities of the illumination on the screen when the mirror is present and when the mirror is removed is: