The curve of binding energy per nucleon as a function of atomic mass number has a sharp peak for helium nucleus. This implies that helium nucleus is

In an extrinsic semiconductor, the number density of holes is $$4 \times 10^{20} \mathrm{~m}^{-3}$$. If the number density of intrinsic carriers is $$1.2 \times 10^{15} \mathbf{m}^3$$, the number density of electrons in it is

Pieces of copper and of silicon are initially at room temperature. Both are heated to temperature T. The conductivity of

The formation of depletion region in a $$p$$-$$n$$ junction diode is due to