N-P-N transistors are preferred to P-N-P transistors because they have

For transistor action 

(1) Base, emitter, and collector regions should have similar size and doping concentration

(2) Base regions must be very thin and lightly doped

(3) The emitter-base junction is forward biased and base, collector junction is reverse biased

(4) Both the emitter-base junction and the base-collection junction is forward biased

Which of the following pairs of statements is correct?

In a common emitter transistor amplifier, the output resistance is $500 \mathrm{K}\Omega$ and the current gain $\beta =49.$ If the power gain of the amplifier is $5\times {10}^6,$ the input resistance is

A transistor oscillator is

(i) an amplifier with positive feedback

(ii) an amplifier with reduced gain

(iii) the one in which dc supply energy is converted into ac output energy. Then