Lecture 3

Question 1

1. The process by which AC is converted to DC is called?
2. Rectification is done by a _____.’
3. What is used the smooth the current and make it even?

Answer 1

1.Rectification

2. Diode
3. Capacitors

Question 2

1. What are the two main types of rectification?
2. Half wave rectification rectifies the AC flowing in ____ direction(s), whereas full wave rectification rectifies current flowing in _____ direction(s).
3. Rectifier circuits small home devices are ____ phase; Rectifier circuits for industrial electrical equipment are ______ phase.

Answer 2

1. Half wave & full wave
2. one; both
3. single; triple

Question 3

1. In half wave rectif. of a single phase supply, which half of the AC wave is allowed to pass? Is this an efficient utilization of power, why or why not?
2. In full wave rectif., which half of the AC wave is allowed to pass?
3. Which (half or full wave rectif) needs more filtering?

Answer 3

1. Either the positive or negative half is allowed to pass. It’s an inefficient utilization of power because the mean voltage is low due to only one phase being conducted
2. Both the positive & negative half of the AC wave is allowed to pass.
3. Half

Question 4

The thermionic diode valve consists of _____ _____ in a(n) _______ _______ ______

Answer 4

two electrodes; evacuated glass envelope

Question 5

1. What type of transformer does the thermionic diode valve operation need and why?
2. At what point will there be no flow of electrons between the cathode & anode?

Answer 5

1. It needs a step down transformer to provide the necessary heating current.
2. When the cathode is positive and the anode is negative.

Question 6

1. Why is it important that the valve not reach its critical operating heat value?
2. Why is the maintenance of a vacuum environment essential to the effective functioning of the valve?

Answer 6

1. Because the diode would cease acting as a valve and current would be conducted in both directions.
2. In the presence of an anode & a vacuum environment, it prevents the electrons that are escaped from the metal surface from being attracted back to the metal surface.

Question 7

1. Why do solid state rectifiers do not utilize a step-down transformer?
2. Give 3 characteristics of the solid state rectifier in comparison to the thermionic diode

Answer 7

1. Solid state rectifiers do not utilize step-down transformer as no heating is required.
2. Less space is taken up, more reliable & longer life span.

Question 8

How may the conductivity of a semiconductor be improved?

Answer 8

By adding an impurity

Question 9

What are the two types of impurities that may be added to a semiconductor to improve its conductivity?

Answer 9

N type materials & P type materials

Question 10

1. N-type carriers are made up of _______. They provide electrons to the _____ _____ of the ________.
2. The electrons are provided at the energy level _____ _____ than the conduction band energy level of the semiconductor.
3. What occurs when voltage or potential difference is applied across the material?
4. Give two (2) examples of N-type carriers.

Answer 10

1. electrons; valence band; semiconductor
2. slightly less
3. Energy is gained & the electrons are now able to move to the conduction band of the semiconductor
4. Phosphorous, Arsenic

Question 11

1. If an impurity is added to the semiconductor that provides an energy level just higher than the valence band, when a potential difference is applied electrons will then move from the ______ _____ to a ______ ______ energy level.
2. Give two (2) examples of P-type carriers.

Answer 11

1. filled band; slightly higher
2. Boron, Idium

Question 12

1. If no voltage is applied to the p or n type semiconductor, what will occur?
2. If a n-type semiconductor is fused with a p-type semiconductor, what will occur?

Answer 12

1. There will be no electron flow as they will be electrically neutral.
2. There will be a small & short flow of electrons generating about 0.1V of potential difference.

Question 13

1. The layer that loses the electrons is referred to as the ______________ ?
2. When a voltage is applied across the semiconductor, there is a movement of _____ through the material towards the junction in one direction & a movement of ______ towards the junction in the other direction.

Answer 13

1. Depletion layer
2. electrons; holes