Rohit focused the image of a candle flame on a white screen using a convex lens. He noted down the position of the candle , screen and lens as under : Position of candle = 26.0 cm Position of convex lens = 50.0 cm Position of screen = 74.0 cm i) What is the focal length of the convex lens? ii) Where will the image be formed if he shifts the candle towards the lens at a position of 38 cm? iii) Draw a ray diagram to show the formation of the image in case (ii) as said above?
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i) u =50-26 = 24cm
v = 74-50= 24cm
Therefore , u=v { it is in the centre of the curvature}
2f = 24cm
=> f = 12cm
ii) If he shifts the candle towards the lens at the position of 38cm ,then the image will form at infinity.
v = 74-50= 24cm
Therefore , u=v { it is in the centre of the curvature}
2f = 24cm
=> f = 12cm
ii) If he shifts the candle towards the lens at the position of 38cm ,then the image will form at infinity.
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Answer:
( i ) . Object distance u = 50 - 26 = 24 cm
Image distance v = 74 - 50 = 24 cm .
Since object distance is equal to image distance.
2 f = 24
= > f = 12 cm
So , focal length of object is 12 cm.
( ii ) . u = 50 - 38 = 12 cm
It's mean candle is at focus.
= > Image will form at infinity.
( ii ) Refer to attachment for ray diagram.
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