For reading small letters with a lens:
Explanation:
A concave lens always produces virtual, erect and diminished images and the decrease in the size of the image depends on the position of the object.
Concave lens will shrink the size of the already small letters.
A convex lens produces real and virtual, erect and inverted, diminished, same sized and magnified image of the object, depending upon the position of the object on the principal axis.
When the object is placed between F and 2F of convex lens, an enlarged but inverted image of the object is formed. The magnified image makes it easier to read small letters but the inverted image is undesirable.
When the object is placed at a distance less than the focal length of convex lens, an enlarged and erect image of the object is formed, which makes it easier to read small letters.
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Two plane mirrors are inclined at an angle of 72° . The number of images of a point object placed between them will be
|
(a) 2 |
(b) 3 |
(c) 4 |
(d) 5 |
Two concentric coplanar circular loops of radii 
and 
carry currents of respectively 
and 
in opposite directions (one clockwise and the other anticlockwise.) The magnetic induction at the centre of the loops is half that due to alone at the centre. If 
. the value of 
is
|
(a) 2 |
(b) 1/2 |
(c) 1/4 |
(d) 1 |
Two resistances 
and 
are joined as shown in the figure to two batteries of e.m.f. 
and 
. If is short-circuited, the current through is
|
(a) |
(b) |
(c) |
(d) |
The length of a given cylindrical wire is increased by 100 %. Due to the consequent decrease in diameter the change in the resistance of the wire will be
|
(a) 300 % |
(b) 200 % |
(c) 100 % |
(d) 50 % |
