Question

Lens $ A $ produces a magnification of $ - 0.8 $ whereas lens $ B $ produces a magnification of $ + 0.8 $ . Which one of the following applies to lenses $ A $ and $ B $ ?
(A) Both $ A $ and $ B $ are convex lens
(B) Both $ A $ and $ B $ are concave lens
(C) $ A $ is a concave lens and $ B $ is a convex lens
(D) $ A $ is a convex lens and $ B $ is a concave lens

Answer 1

Hint : Here we just need to find both the lens individually. By comparing the properties of their images formed by the two lenses A and B we can easily determine the type of lens. Generally the convex lens forms a real image while a concave lens forms a virtual image.

Complete Step By Step Answer:
The magnification of the lens is given by the formula:
 $ M = \dfrac{v}{u} $
We know that
Now as the first lens has a negative magnification. It signifies that the lens is a convex lens as the image formed is
a. Real
b. Inverted
c. Diminished
Now as the first lens has a positive magnification. It signifies that the lens is a concave lens as the image formed is
a. Virtual
b. Erect
c. Diminished
Finally we conclude that lens A is convex because it produces negative magnification which signifies that the image is real and inverted while lens B is concave lens because it produces positive magnification which signifies the image is virtual and erect.
Hence the correct option is D.

Note :
Most important thing here is to notice the magnification of the lens as it is the initial and generally most careless state. Apart from that it is necessary to find the properties and relate them to correction. Larger the magnification, the larger the size of the image.