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  • A student 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 the lens as under Position of candle = 12.0 cm Position of convex lens = 50.0 cm

A student-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 the lens under

Position of candle = 12.0 cm

Position of convex lens = 50.0 cm

Position of the screen = 88.0 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 31.0 cm?

(iii) What will be the nature of the image formed if he further shifts the candle towards the lens?

(iv) Draw a ray diagram to show the formation of the image in case (iii) as said above.

Answers (1)

Explanation:-

 

  • Position of candle u = −12 cm (negative because the object is placed to the left of the lens)
  • Position of convex lens v = 50 cm
  • Position of screen v′ = 88 cm (positive as the image is formed on the right side of the lens)

(i) Focal length

= 38 ÷ 2 = 19 cm

(ii) object distance u = 50 – 31 = 19 cm

                In this case, object distance = focal length

                This means that images are formed at infinity.

(iii) If the candle is moved closer to the lens (i.e., u decreases further), the image will remain virtual, erect, and magnified. As the object approaches the lens, the image will move farther away from the lens but will still remain on the same side as the object.

The image formed will be virtual and erect.

(iv) In this case, as the object is moved even closer to the lens, the image formed will remain virtual and magnified. Here’s how the ray diagram can be drawn:

Posted by

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