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Question
How will you decide whether a given piece of glass is a concave lens, convex lens, or a plane glass plate?
Solution
Hold the given piece of glass over some printed number:
(i) If the letter appears magnified, the given piece is a convex lens.
(ii) If the letters appear diminished, the given piece is a concave lens.
(iii) If the letters appear to be of the same size, then it is a plane glass mirror.
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RELATED QUESTIONS
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?
Where should an object be placed so that a real and inverted image of the same size as the object is obtained using a convex lens?
Where should an object be placed in front of a convex lens so as to obtain its virtual, erect and magnified image?
Describe the nature of image formed when an object is placed at a distance of 30 cm from a convex lens of focal length 15 cm.
A convex lens of focal length 15 cm produces a magnification of +4. The object is placed:
(a) at a distance of 15 cm
(b) between 15 cm and 30 cm
(c) at less than 15 cm
(d) beyond 30 cm
An object 50 cm tall is placed on the principal axis of a convex lens. Its 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens.
A convex lens forms an image of an object equal to the size of the object. State two more characteristics of the image.
List four properties of the image formed by a convex mirror.
For which position of the object does a convex lens form a virtual and erect image? Explain with the help of a ray diagram.
Differentiate convex lens and concave lens.
