Semiconductor Electronic: Material, Devices And Simple Circuits — Physics STD 12 Science — Question

Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
Assertion (A): The kinetic energy of a charged particle moving in a uniform magnetic field does not change. Reason (R): In a uniform magnetic field no force acts on the charge particle.

Two identical thin rings, each of radius a meter, are coaxially placed at a distance R meter apart. If Q₁ coulomb and Q₂ coulomb are respectively the charges uniformly spread on the two rings, the work done in moving a charge q coulomb from the centre of one ring to that of the other is:

1A current flows through an infinitely long straight wire. The magnetic field produced at a point 1 metres away from it is

(a)  2

(b)

(c)  2

(d) 2π

When N-type of semiconductor is heated

(a) Number of electrons increases while that of holes decreases

(b) Number of holes increases while that of electrons decreases

(c) Number of electrons and holes remains same

(d) Number of electrons and holes increases equally

The energy of hydrogen atom in its ground state is – 13.6 eV. The energy of the level corresponding  to the quantum number n is equal 5 is

(a) – 5.40 eV

(b) – 2.72 eV

(c) – 0.85 eV

(d) – 0.54 eV

A TV tower has a height of 100 m. The average population density around the tower is 1000 per km². The radius of the earth is 6.4  m. the population covered by the tower is

(a) 2

(b) 3

(c) 4

(d) 6

A white screen illuminated by green and red light appears to be

(a) Green

(b) Red

(c) Yellow

(d) White

Which one of the following is a safe place during lightning?