A charged ball B hangs from a silk thread S, which makes an angle θ with a large charged conducting sheet P, as shown in the figure. The surface charge density σ of the sheet is proportional to
|
(a) sin θ |
(b) tan θ |
(c) cos θ |
(c) cos θ |
(b) tan θ
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A candle placed 25 cm from a lens, forms an image on a screen placed 75 cm on the other end of the lens. The focal length and type of the lens should be
|
(a) + 18.75 cm and convex lens |
(b) – 18.75 cm and concave lens |
|
(c) + 20.25 cm and convex lens |
(d) – 20.25 cm and concave lens |
The armature of dc motor has 20Ω resistance. It draws current of 1.5 ampere when run by 220 volts dc supply. The value of back e.m.f. induced in it will be
|
(a) 150 V |
(b) 170 V |
(c) 180 V |
(d) 190 V |
Two spheres of radius a and b respectively are charged and joined by a wire. The ratio of electric field of the spheres is
|
(a) a/b |
(b) b/a |
(c) |
(d) |
