Advertisement Remove all ads

An Image Formed on a Screen is Three Times the Size of the Object. the Object and Screen Are 80 Cm Apart When the Image is Sharply Focussed. Calculate Focal Length of the Lens. - Science

An image formed on a screen is three times the size of the object. The object and screen are 80 cm apart when the image is sharply focussed. 

 Calculate focal length of the lens.

Advertisement Remove all ads

Solution

Magnification (m) = 3
Object distance (u) = ?
Image distance (v) = ?
Focal length (f) = ?
Distance between image and object (v + u) = 80 cm
v = 80-u
We know that: 

`m=v/u` 

`or 3=(80-u)/u` 

`or 3u=80-u` 

`or 4u=80` 

`or u=20cm` 

thus, v=80-u 

=80-20=60 cm 

Putting these values in lens formula, we get: 

`1/v-1/u=1/f` 

`1/60-1/-20=1/f` 

`(1+3)/60=1/f`  

`f=60/4=15 cm`

  Is there an error in this question or solution?
Advertisement Remove all ads

APPEARS IN

Lakhmir Singh Class 10 Physics (Science)
Chapter 5 Refraction of Light
Q 20.2 | Page 257
Advertisement Remove all ads

Video TutorialsVIEW ALL [1]

Advertisement Remove all ads
Share
Notifications

View all notifications


      Forgot password?
View in app×