State Bohr’s postulate to define stable orbits in hydrogen atom. How does de Broglie’s hypothesis explain the stability of these orbits?

A hydrogen atom initially in the ground state absorbs a photon which excites it to the n = 4 level. Estimate the frequency of the photon.

Explain the processes of nuclear fission and nuclear fusion by using the plot of binding energy per nucleon (BE/A) versus the mass number A.

A radioactive isotope has a half-life of 10 years. How long will it take for the activity to reduce to 3.125 %?

A student wants to use two p-n junction diodes to convert alternating current into direct current. Draw the labelled circuit diagram she would use and explain how it works.

Give the truth table and circuit symbol for NAND gate.

Draw the typical input and output characteristics of an n-p-n transistor in CE configuration. Show how these characteristics can be used to determine (a) the input resistance (r_i), and (b) current amplification factor.

38.

Give three reasons why the modulation of a message signal is necessary for long-distance transmission.

Show graphically an audio signal, a carrier wave and an amplitude modulated wave.

Draw a ray diagram to show image formation when the concave mirror produces a real, inverted and magnified image of the object.