The expected responses were:

(a)        The main difference is that the Colpitts oscillator  uses a tapped capacitor while Hartley’s oscillator  uses a tapped inductor arrangement.
(b)        Conditions for oscillation

• Positive feedback
• Magnitude of product of open loop gain and feedback factor = 1
• Phase of product of open loop gain and feedback factor = 0 or 2k pi                                                                       

(c)       Other types of Transistor oscillator types

• Wien Bridge oscillator
• Relaxation oscillators
• Crystal oscillators
• Phase shift oscillator
• Negative resistance oscillator
• Voltage-controlled oscillator
• Armstrong (or Tickler) oscillator
• Tuned collector oscillator

(d)        Expression for frequency of a series RLC circuit ar resonance
At resonance, and in terms of capacitance ‘C’, and inductance L’, frequency is given by
                                                                                                                                       
According to the Chief Examiner, while majority of the candidates that attempted this question were able to list the different types of oscillators, a few of them could not recall the expression for resonance frequency of the RLC circuit.