Electrostatics — Physics STD 12 Science — Question

A hollow copper sphere A and a solid sphere B of equal radius are charged with the same potential. The true statement is:

Which impurity is doped in Si to form N-type semi-conductor?

(a) Al

(b) B

(c) As

(d) None of these

The internal resistance of a cell depends on

(a) The distance between the plates	(b) The area of the plates immersed
(c) The concentration of the electrolyte	(d) All the above

In a meter bridge the point D is a neutral point (Fig).

An object placed 10 cm in front of a lens has an image 20 cm behind the lens. What is the power of the lens (in dioptres)

(a) 1.5

(b) 3.0

(c) – 15.0

(d) + 15.0

Work function of a metal is 2.51 eV. Its threshold frequency is

(a) 5.9  cycle/sec	(b) 6.5  cycle/sec
(c) 9.4  cycle/sec	(d) 6.08  cycle/sec

A nichrome wire 50 cm long and one square millimetre cross-section carries a current of 4A when connected to a 2V battery.  The resistivity of nichrome wire in ohm metre is

(a) 1

(b) 4

(c) 3

(d) 2

If the velocity of a charged particle is made twice and that of magnetic field is made half then the radius of the circular path of the charged particle in the magnetic field will become :

Rest mass energy of an electron is 0.54 MeV. If velocity of the electron is 0.8 c, then K.E. of the electron is

(a) 0.36 MeV

(b) 0.41 MeV

(c) 0.48 MeV

(d) 1.32 MeV

Magnetic induction is a

(a) Scalar quantity

(b) Vector quantity

(c) Both (a) and (b)

(d) None of the above