real image of lens is twice size of object .f= 15 cm.u=?
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Let size of object be x cm
So, size of image = 2x cm
f = 15cm
u = ?
We know,
m=height of object/height of image = f - v/f
2x/x = 15 - v/ 15
15-v = 30
v = -15cm
Also,
1/f = 1/v - 1/u
1/15 = 1/-15 - 1/u
-1/u = 1/15 + 1/15
1/u = -2/15
u = -15/2 = -7.5cm
So, size of image = 2x cm
f = 15cm
u = ?
We know,
m=height of object/height of image = f - v/f
2x/x = 15 - v/ 15
15-v = 30
v = -15cm
Also,
1/f = 1/v - 1/u
1/15 = 1/-15 - 1/u
-1/u = 1/15 + 1/15
1/u = -2/15
u = -15/2 = -7.5cm
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