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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 16th March 2019, 7:15 PM
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 Expert 16th March 2019, 8:12 PM
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