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Question
Define the principal focus of a convex lens.
Solution
For a convex lens, the principal focus is a point on the principal axis of a convex lens at which the rays of light originally parallel and close to the principal axis of the lens pass through it after refraction by the lens.
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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?
For what position of an object a real, diminished image is formed by a convex lens?
State whether convex lens has a real focus or a virtual focus.
Find the nature, position and magnification of the images formed by a convex lens of focal length 0.20 m if the object is placed at a distance of:
0.25 m
Study the diagram below.
what are the points O, O’ called?
Observe the following figure and answer the questions.
a) Which optical instrument shows arrangement of lenses as shown in the figure?
b) Write in brief the working of this optical instrument.
c) How can we get different magnifications in this optical instrument?
d) Draw the figure again and labelled it properly
(a) What type of a lens can be used as a magnifying glass?
(b) Show by a ray diagram the formation of a real image by simple magnifying lens.
Simple microscope : Number of convex lens one : : compound microscope : _______
- In which type of microscope do you find the lens arrangement as shown in the following diagram?
- Write about the working and the use of this microscope.
The above image shows a thin lens with a focal length of 5m.
- What is the kind of lens shown in the above figure?
- If a real inverted image is to be formed by this lens at a distance of 7m from the optical centre, then show with calculation where should the object be placed.
- Draw a neatly labelled diagram of the image formation mentioned in (ii).
