A student places a candle flame at a distance of about 60 cm from a convex lens of focal length 10 cm and focuses the image of the flame on a screen. After that he gradually moves the flame towards the lens and each time focuses the image on the screen. (a) In which direction-toward or away from the lens, does he move the screen to focus the image?
(b) How does the size of the image change?
(c) How does the intensity of the image change as the flame moves towards the lens?
(d) Approximately for what distance between the flame and the lens, the image formed on the screen is inverted and of the same size?
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(a) The student moves the lens away from the screen to focus the image because on moving the candle towards the lens, the image distance increases.
(b)The size of the image increases when the object is moved towards the lens.
(c) Intensity of the image decreases.
(d) When the candle is moved very close to the lens, no image is formed on the screen. A virtual image is formed behind the candle on the same side of the screen.
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(a) The student moves the screen away from the lens to focus the image.
(b) The size of the image decreases.
(c) The intensity of the image decreases.
(d) About 20 cm between the flame and the lens, the image formed on the screen is inverted and of the same size
Explanation:
- The screen is always moved away from convex lens to focus. This is because convex lens diverges.
- When the lens is moved away from the lens, then the size of the image decreases and vice-versa.
- When the object is moved towards the lens, the object blurs and intensity decreases.
- When the object is moved close, there is no image but there is virtual image formed on the same side of the screen.
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