Quantum Mechanics Answers

If the same force is applied to a ping-pong ball and to a tennis ball that are initially at rest, which ball will move faster?(Assume that there is no friction between the ball and the table.)Explain.

If sigma x, sigma y, and sigma z are three components of a pauli spin matrix sigma, then show that [sigma x, sigma y]=2i sigma z; [sigma y, sigma z]= 2i sigma x

If quantum physics formulas are not applicable at subatomic levels, why do we still use them for deriving relations at the subatomic level ?
Ex. if equations of motions are not applicable at subatomic level , why do we use the equations to explain the path of an electron moving perpendicular to electric field ?

4. A boy stands at the centre of a turn table with his two arms stretched. The turn table is set rotating with an angular with an angular speed of 40 r.p.m. How much is the angular speed of the boy if he folds his hands back and thereby reduces his moment of inertia to 2/5times the initial? Assume the turn table to rotate without friction.

How can we calculate the value of normalisation constant when the electron wave function is given with the range

In an ideal 3:17 step-up transformer, the primary power is 34 kW and the secondary current is 30 A. The primary voltage is:


A. 6.25 V

B. 200 V

C. 1133.3 V

D. 6422.2 V

E. 51 V

Consider nuclei with small mass number A such that .

N = Z =A/2. Neglecting
pairing term (∈) show that semi-empirical formula is given by

BE/A = α −βA(to the power -1/3)− δA(to the power 2/3) / 4.
Obtain the value of A and Z for which binding energy per nucleon (BE / A) is
maximum. Take β = 17 ,8. δ = 71.0 .

Plot a graph between binding energy per nucleon as a function of mass number.
Write the main features of the curve.

A radioactive substance of 1 g is reduced to 2.1 mg in 5 years by alpha decay.
Calculate the half-life of the substance

A photon of energy 8ev is incident on a metal surface of threshold frequency 1.6/1000000000000000 Hz . The kinetic energy of the photoelectrons emitted is (in ev ) (1) 6. (2) 1.6 (3) 1.2. (4) 2