Tom atempts an ophcs dem o This is his set-up an upside down arrow (4) is onmed

Question

Tom atempts an ophcs dem o This is his set-up an upside down arrow (4) is onmed on a soeen that is 25 cm o the ofa thin convex polycadw nate lens (tens 2) with a ractius or curvature of 12 cm. This lens (lens z) is 20 cm the rigkt of anofher lens Clens ), and 75cm t the right of the objeef (an arrow) . what is the vergence of the image leaving the 2nd eens (lens 2)? 2) what is the power of the znal lens (lens 2)? 3) what is the power of the I5t lens (lens )? t) what is the vergence of -the object when it strikes the 5t lens (iens d 5) Is the object rea/ virtval? 6) Is the object erectlinverted? 7) Is the image form ed by the lens (iens 1) reavirtual? )Is the im age formed by tHe ia lens Clens 2) real/wituu

Explanation / Answer

(1). since the image formed by convex lens 2 is upside down, and also the image distance is greated than radius of curvature of the lens. Hence, the image will be real, inverted and larger than the object (in this case image formed by lens 1)

(2). power of lens = 1/f = 1/0.06 = 16.67 D (as radius of curvature is 12cm , so focus will be 6 cm)

(3).using formula, 1/v -1/u = 1/f, we find image (which acts as object for lens 2) to be 7.89cm.

i.e. 1/25 - 1/u = 1/6 , or, 1/u = 1/25 - 1/6 , or, u = - 25*6/19 = - 7.89 cm.

so now, this is image of lens 1 and the image distance is (20-7.89) = 12.11cm

also object distance for lens 1 is (75 - 20)= 55 cm

therefore, using formula, 1/v -1/u = 1/f, we have,

1/(12.11) - 1/-55 = 1/f , or 1/f = 1/12.11 + 1/55,

f = 55*12.11/67.11 = 9.92 cm

therefore, power = 100/ 9.92 = 10.08 D

(4).the object must be inverted as the image formed is found to be erect by lens 1. the object must be kept beyond center of curvature of lens1.

(5). the object must be real as we find a real image after refraction through lens 2.

(6)The object is inverted because we get erect image after refraction through lens1.

(7). yes, the image formed by first lens (lens 1) is real.

(8). yes, the image formed by lens2 is real as we get image projected on a screen.

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