A converging lens, of focal length 100 mm has an object placed 200 mm in front o

Question

A converging lens, of focal length 100 mm has an object placed 200 mm in front of it. a) The image is therefore 300 mm behind the lens 100 mm in front of the lens 50 mm behind the lens 200 mm behind the lens 50 mm in front of the lens The object is now moved to a new position 50 mm in front of the lens. b) The image is now located 50 mm behind the lens 100 mm behind the lens 100 mm in front of the lens 150 mm in front of the lens 50 mm in front of the lens c) The image of the object is Magnified by 2

Explanation / Answer

A converging lens has a focal length of 200 mm. An object is placed at the following distances from the lens (a) 500 mm, (b) 200 mm and (c) 150 mm. In each case, use the lens equation to calculate the IMAGE POSITION


I prefer the conventional symbols ..
u = object distance
v = image distance
f = focal length .. [f is +ve (real) for converging lens]

1/u + 1/v = 1/f ..
1/v = 1/f - 1/u
a)
1/v = 1/200 - 1/500 = 0.003 .. .. v = 333.30 mm (real, on opposite side of lens to object)
b)
1/v = 1/200 - 1/200 = 0 .. .. v = infinity
c)
1/v = 1/200 - 1/150 = - 0.00167 .. .. v = - 600 mm ..(image is virtual, at 600mm on same side as object)

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