IF SOMEONE IS ONLINE PLEASE ANS THESE Qs FASSTT!! GOT BOARDSSS!!!!!

1. Two thin lenses of focal lengths 10 cm and -5 cm are kept in contact. What is the focal length and power of the combination?

2. An image 2 cm high is placed at a distance of 16 cm from a concave mirror which produces a real image 3 cm high. Find the position of the image and the focal length of the mirror.

3. An object placed at a distance of 10 cm from a concave mirror produced an infinitely large image at the infinity. The focal length of the mirror is?

4. A concave mirror produces a real inverted image of the same size as that of the object. If the object is placed at a distance of 16 cm from the mirror, the focal length of the mirror is?

1

Answers

The Brainliest Answer!
2015-04-12T12:07:50+05:30

This Is a Certified Answer

×
Certified answers contain reliable, trustworthy information vouched for by a hand-picked team of experts. Brainly has millions of high quality answers, all of them carefully moderated by our most trusted community members, but certified answers are the finest of the finest.
1.    f1 = 10 cm = 0.1 m              f2 = - 5 cm = - 0.05 m
       P1 = power of first lens = 1/f1 = 10 Dioptres
     P2 = 1/f2 = - 20 dioptres
     combination power = P = P1 + P2 = 10 - 20 Dioptres = -10 D
     combination focal length = 1/ P = -1/10 m = -10 cm

2.    h = 2cm    u = -16 cm
         h' = 3 cm erect   or  - 3 cm inverted
     case 1:
                 m = h'/h = 1.5 = -v/u   
               v = - 1.5 u = 24 cm
               1/f = 1/v+ 1/u = 1/24 - 1/16 = -1/48
                     f = - 48 cm
   case 2 :
              h' = -3 cm        m = -1.5
              v = 1.5 u  = - 24  cm
              1/f = -1/24 + 1/16 = 1/48
                   f = 48 cm

3.   u = -10 cm      v = infinity            m = infinity
         1/f = 1/u + 1/v = -1/10 + 1/infinity = -1/10
             f = -10 cm
     When an object is placed at the focus of the mirror, it produces an image at infinity.  When parallel rays from infinite distance fall on the mirror, they produce an image at the focus.

4.    h' = - h        m = -1
         u = -16 cm    =>  v = -  m u =  - 16 cm
       1/f = -1/16 -1/16 = -1/8
         f = - 8 cm

     When an object is placed at the center of curvature C of the concave mirror with focal length f, then it produces an image inverted at the same place ie., center of curvature. 
       then u = - R =  2 f      hence,  f = - R/2 =  u/2

2 5 2