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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, 07:15: PM
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
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.
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, 08:12: PM
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