Basic Electronics Paper 2, WASSCE (SC), 2017

Question 5

 

  1. State four advantages of the transistor over the thermionic valve.
  2. Draw and label the circuit symbol of a p-channel Field Effect Transistor.
  3. A transistor amplifier connected in common emitter mode has a collector load resistance of 2000Ω. If the short-circuit current gain (hfe) of the transistor is 100 and its input resistance (Rin) is 1000Ω. Calculate the voltage gain.

 

Observation

 

The expected answers were;
    (a)    Advantages of Transistor over Thermionic Valve
            -  Higher efficiencies.
            -  Transistors consume less power than thermionic valves.
            -  Transistors are smaller in size compared to thermionic valves.
            -  Transistors require less working voltage.
            -   Lower cost
            -  Fast switching
            -  Severaltransistors can be integrated on a single chip
                                                           
            P-channel FET symbol
       
                                                                                                                       
        (c)   hfe    =  100
               Rin    =  1,000 Ω
               RL     =  2,000 Ω

  1. Voltage gain (Av)           

                                   

Only a few candidates could state the advantages of transistor over vacuum tube valve.      
Generally, candidates’ responses to question were poor.