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** **__Solve this:__

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 it he shifts the candle towards the at a position Of 38 cm

(III) Draw a ray diagram to show the formation Of the image in case (ii) as said above.

__Solve this:__

Dear Student

Here, we will measure all distance with respect to the position of convex lens.

so,

the object distance will be, u = 26 cm - 50 cm = -24 cm

the image distance will be, v = 74.0 cm - 50 cm = 24 cm

(1)

so, the focal length will be calculated using the lens formula

1/f = 1/v - 1/u

or

1/f = (2 / 24)

thus, the focal length fot he lens is

f = 12 cm

(2)

here,

the image distance will be, u = 38 cm - 50 cm = -12cm

and focal length, f = 12 cm

so,

1/v = 1/f + 1/u

or

1/v = 1/12 - 1/12

so,

v = infinity, the image will be formed at infinity as the object is kept on the point of focus of the lens.

(c)

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