By using a convex lens, a student obtained a sharp image of this classroom window grill on a screen. In which direction should we move the lens to focus a distant tree instead of the grill?
a) Towards the screen
b) Away from the screen
c) Very far from the screen
d) Behind the screen
Answers
The distance between lens and image reduces. Therefore, the lens should moved towards the screen.
Explanation:
- We know that placement of lenses at different places can change the formation of image to where it is needed.
- Here we are given a convex lens and the student is set to be focusing it on the grill while the focus needs to be on the tree that is placed outside the grill.
- We will consider the placement of tree at Infinity so to get an image near focus when the object is placed at Infinity.
- The lens should move towards the screen to get a clear picture of the tree placed outside the grill.
To know more:
A student obtain clear image of window grills on the screen but the teacher told him to get the image of tree far away instead of window . To get a clear image the lens must be
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Three students measured the focal length of a convex lens using parallel rays from a distant object. All of them measured the distance between the lens and the inverted image on the screen. Student A saw a sharp image on the screen and labelled the distance as f1. Student B saw a slightly larger blurred image on the screen and labelled the distance as f2. Student C saw a slightly smaller blurred image on the screen and labelled the distance as f3. The relation between the three measurements would most likely be (a) f1 = f2 = f3. (b) f1 < f2 and f3. (c) f3 < f1 < f2. (d) f1 < f2 and f1= f3. The ans is (c) but how???
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