CH5 Flashcards
Definition of Thermionic emission
Emission of free electrons from a heated metal surface
Factors that increases thermionic emission
Increased temperature
Large surface area of metal
Metal coated with metal oxide
Definition of Cathode ray
Beams of electron in vacuum that moves in high speed
Direction of Cathode ray with normal condition
Cathode to Anode
Direction of Cathode ray with deflection tube
Cathode to anode Towards positive plate
Energy change of cathode
Electrical-Kinetic-Light
Function of semiconductor diode
allows electric current to flow in one direction only
Definition of rectification
Process of converting alternating current into direct current
How reverse biased circuit allow electric current (4m)
In reverse biased diode, holes and electron move away from depletion layer in opposite direction
Depletion layer become thicker
Junction voltage increases until reaches potential difference of battery
resistance of diode becomes very high
How forward biased diode allow electric current
Holes move toward n-type semiconductor and electron move toward p-type semiconductor.
depletion layer becomes thinner
Resistance of the diode becomes very small
Junction voltage decreases
Conversion into Positive Current by Half-Wave rectification (4m)
A complete alternating current consists of Positive half-cycle and negative half-cycle.
During positive half cycle, semiconductor diode is forward biased and allow current to flow
During negative half-cycle, semiconductor diode is reverse biased and allow no current flow.
Electric current with no negative half-cycles is produced
Definition of Full wave rectification
Process where both halves of the alternating wave cycle is made to flow in a same direction
Working mechanism of smoothing current by Capacitor (4m)
Capacitor is connected parallel to the load.
When potential difference increases, capacitor is charged and stores energy
When potential difference decreases, capacitor is discharged to ensure current does not fall to zero as energy stored in capacitor maintain potential difference across the resistor
Output current become smooth
Function of transistor base
Control flow of charge form emitter to collector
Function of transistor collector
receive charge carrier from emitter
Function of transistor emitter
supply charge carrier to collector
Working mechanism of a transistor circuit when switch is closed
Base bulb is dim because base resistance is high and base current is very small.
Collector bulb lights up very brightly because collector current > base current
Working mechanism of in dark LDR
Resistance of LDR is very high
Voltage of LDR exceeds minimum voltage across B and E
Base current flow to turn on resistor
High collector current flow in the collector circuit and bulb light up
Working mechanism of Thermistor in high temperature
Resistance and voltage decrease
Voltage across base resistor increase until exceeds minimum voltage across B and E
Base current flow and Transistor turn on
High collector current flows
