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

A freshly prepared radioactive source of half-life 2h emits radiation of intensity which is 64 times the permissible safe level. The minimum time after which it would be possible to work safely with this source is:

Electric conduction takes place in a discharge tube due to the movement of:

1. Positive ions.
2. Negative ions.
3. Electrons.
4. Protons.

Photoelectric effect is the phenomenon in which?

For a thermocouple, the temperature of inversion is that temperature at which thermo e.m.f. is

(a) Zero

(b) Maximum

(c) Minimum

(d) None of the above

Wires P and Q have the same resistance at ordinary (room) temperature. When heated, resistance of P  increases and that of Q decreases. We conclude that

(a) P and Q are conductors of different materials

(b) P is N-type semiconductor and Q is P-type semiconductor

(c) P is semiconductor and Q is conductor

(d) P is conductor and Q is semiconductor

Two equal positive charges are kept at points A and B. The electric potential at the points between A and B (excluding these points) is studied while moving from A to B. The potential.

A toroid of n turns, mean radius R and cross-sectional radius a carries current I. It is placed on a horizontal table taken as x-y plane. It's magnetic moment m:

In a certain charge distribution, all points having zero potential can be joined by a circle S. Points inside S have positive potential and points outside S have negative potential. A positive charge, which is free to move, is placed inside S

(a) It will remain in equilibrium

(b) It can move inside S, but it cannot cross S

(c) It must cross S at some time

(d) It may move, but will ultimately return to its starting point

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:

With the decrease in the wave length of the incident radiation the velocity of the photoelectrons emitted from a given metal