Question

Q4. Give reason for the following:

a) Convex lens is used in projectors in cinema houses.

b) Convex mirror is used as rear view and side view mirrors in a vehicle.

c) A piece of paper catches fire when sunlight is converged at a point on it

with the help of a magnifying glass.

d) There is no real focus of a concave lens.
Class 7 , Science​

Answer 1

1. Convex Lens is used in projector to get magnified image as shown in figure. Convex Lens is placed in front of object that object is between F and 2F.
2. We prefer a convex mirror as a rear-view mirror in vehicles because it gives a wider field of view, which allows the driver to see most of the traffic behind him. Convex mirrors always form a virtual, erect, and diminished image of the objects placed in front of it.
3. When sun rays fall on the convex lens they get converged to a point. ... These rays surely have heat energy and they get accumulated in that point. When the amount of rays have accumulated enough so as to reach the ignition temperature of paper, the paper catches fire. Thus the paper is burnt.
4. A convex lens is said to have real focus and a concave lens a virtual focus. Why? A convex lens converge light rays at its focus therefore it is said to produce real focus whereas the concave lens diverges the light rays that seems to come from focus therefore it is virtual.

hope it helped uh ❤️