4.1)  

4.1.2)  

When the transistor operates in the active region its base-emitter junction is reverse biased and base-collector junction is forward biased.

The above statement is false, because the transistor is said to be operated in active region when the emitter - base junction is forward biased and collector – base junction is reverse biased.

4.1.3)

Power amplifiers are designed to handle large signals.

The above statement is true, because power amplifiers as their name suggests, the main job of a “ Power Amplifier ” (also known as a large signal amplifier), is to deliver power to the load, and the product of the voltage and current applied to the load with the output signal power being greater than the input signal power.

4.1.4)

Uni-junction diode is a single junction device, which has negative resistance characteristics.

The above statement is true, because the device has only one junction, so it is called the uni-junction device.

UJT is operated with emitter junction forward- biased while the JFET is normally operated with the gate junction reverse-biased.UJT does not have ability to amplify but it has the ability to control a large ac power with a small signal. It exhibits a negative resistance characteristic and so it can be employed as an oscillator.

4.1.5)

Field-effect transistors are relatively unaffected by radiation

The above statement is false, because the field-effect transistor can tolerate a much higher level of radiation since they do not rely on minority carriers for their operation.

4.1.4)

In an N-channel JFET the majority carriers are electrons.

The above statement is true, because depending upon the majority carriers,  JFET has been classified into two types,

(1) N-channel JFET with electrons as the majority carriers.

(2) P-channel JFET with holes as the majority carriers.