PHY301 Final Term Subjective

Fall 2012

1. State kirchhoff’s current law (KCL) Marks: 2:

Answer: (PAGE 42)

KIRCHHOF’S CURRENT LAW

Sum of all the currents entering in the node is equal to sum of currents leaving the node. It can also be defined as

sum of entering currents + sum of leaving currents =0

2. If we want to find Vout by superposition, what type of replacement we will do with voltage and current source? Just draw the diagrams.

Answer: (PAGE 92)

“ In any linear circuit containing multiple sources, the current or voltage at any point in the circuit may be calculated as the algebraic sum of the individual contributions of each source acting alone.”

3. State the superposition theorem.

Answer: (PAGE 92)

The principle of superposition, which provides us with the ability to reduce a complicated problem to several easier problems – each containing only a single independent source – states that “ In any linear circuit containing multiple sources, the current or voltage at any point in the circuit may be calculated as the algebraic sum of the individual contributions of each source acting alone.” 5. Differentiate between half wave and full wave rectifier.

Answer: The difference between a half wave rectifier and and full wave rectifier is that a half wave rectifier removes one of the positive or the negative half cycle of the wave and only either half of the cycle appears in the output whereas in the full wave rectifier both the cycles appear in the positive or negative cycle of the output. The efficiency of a full wave rectifier (81.2%) is too double of a half wave rectifier(40.6%) because the r.m.s. value in case of a full wave rectifier is Maximum current divided by 1.41 (under root of 2) whereas in case of a half wave rectifier the r.m.s current is half of maximum current during the wave cycle.

full-wave.aspx

OR

Half Wave Rectifier: A half wave rectifier is a special case of a clipper. In half wave rectification, either the positive or negative half of the AC wave is passed easily, while the other half is blocked, depending on the polarity of the rectifier. Because only one half of the input waveform reaches the output, it is very inefficient if used for power transfer. Half-wave rectification can be achieved with a single diode in a one phase supply. Full Wave Rectifier: A full-wave rectifier converts the whole of the input waveform to one of constant polarity (positive or negative) at its output. Full-wave rectification converts both polarities of the input waveform to DC (direct current), and is more efficient. However, in a circuit with a non-center tapped transformer, four diodes are required instead of the one needed for half-wave rectification. (From other past papers)

6. Conduction band and valence band.

Valence band is the highest range of electron energies in which the electrons are normally present at absolute zero temperature.

This is the range of electron energies enough to free an electron from binding with its atom to move freely within the atomic lattice of the material.