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1. A concave mirrow has a focal length of 20cms find the position or positions of an object for which the image size is double of the object size . 2. A one cm object is placed perpendicular to the principal access of a convex mirror of focal lenght 7.5cms . find its distance from the mirror if the image formed is 0.6cm in size. 3.A candle flame 1.6cm is imaged in a ball baring of the diameter 0.4cm , if the ball baring is 20cm away from the flame, find the location and height of the image.  
Asked by sridhark91 | 16 Mar, 2019, 19:15: PM
answered-by-expert Expert Answer
1)Image can be  virtual => m = 2,  v = - 2 u     
1/-2u  + 1/u   = 1/-20      =>  u = -10cm   
 image real, 
 m = -2,   v = 2 u     
  1/2u + 1/u = 1/-20       =>   u = -30 cm   
 two positions
2)  1/v + 1/u = 1/f     
1/v + 1/-7.5  = 1/6   
 =>  v = 3.33 cm   a virtual erect image is formed.       
magnification = 3.33/7.5 = 4/9    so image size =  3 * 4/9 = 4/3 cm
3)     u is so high that 1/u is nearly negligible as compared to 1/f. 
Hence 1/v = 1/-7.6              v = nearly  - 7.6 cm.   
   m = - 7.6/380,000,000         
 - h'/h = m         
  =>   h' =  - 7.6 * 3450 /380,000 = - 0.069 meters           
 h' = 6.9 cm   
=> diameter of the image formed by mirror at 7.6 metes or focus
Answered by Ankit K | 16 Mar, 2019, 20:12: PM
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