Is` p= E/c `valid for electrons?

In the derivation of P_1-P_2=rhogz it was asumed that the liquid is incompressible. Why will this equation not be stictly valid for a compressible liquid?

An electric dipole of moment p is placed in a uniform electric field E. Then (i) the torque on the dipole is p xx E , (ii) the potential energy of the system is p.E, (iii) the resultant force on the dipole is zero

Lets n_p and n_e be the number of holes and conduction electrons in an intrinsic semiconductor.

Lets n_p and n_e be the number of holes and conduction electrons in an extrinsic semiconductor.

Consider a neutrom and an electron bound to each other due to gravitational force. Assuming Bohr's quantization rule angular momentum to be valid in this case, derive an expression for the energy of the neutron-electron system.

An electron is moving in a circular path under the influence of a transverse magnetic field of 3.57xx 10^(-2) T. If the value of e//m is 1.76xx10^(11)C//kg , the frequency of revolution of the electron is:

The ground state energy of hydrogen atom is -13.6 eV. What are k.E & P.E of the electron in this state?

If 'm' is the mass of an electron and 'c' is the speed of light, the ratio of the wavelength of a photon of energy E to that of the electron of the same energy is