Test on The transistor as a switch and an amplifier

Question 1: An NPN Bipolar Junction Transistor is composed of two N-type semiconductor layers separated by a P-type semiconductor layer.

A. Yes

B. No

Explanation: An NPN BJT is described as a three-layer semiconductor device composed of two N-type semiconductor layers separated by a P-type semiconductor layer.

Question 2: Which of the following statements accurately describes the primary function of a specific terminal in an NPN Bipolar Junction Transistor?

A. The Collector (C) is heavily doped to emit a large number of charge carriers into the base region.

B. The Base (B) is a very thin and lightly doped middle layer that controls the flow of current from the collector to the emitter.

C. The Emitter (E) is moderately doped and its main purpose is to collect the charge carriers emitted by the base.

D. The Collector (C) is moderately doped and its main purpose is to collect the charge carriers emitted by the emitter and passed through the base.

Explanation: The study material states that the Base (B) is a very thin and lightly doped middle layer, whose primary function is to control the flow of current from the collector to the emitter. It also specifies that the Collector (C) is moderately doped and its main purpose is to collect the charge carriers emitted by the emitter and passed through the base. The Emitter (E) is heavily doped to emit charge carriers, not moderately doped to collect them, making option 2 incorrect. Option 0 incorrectly attributes the emitter's doping and function to the collector.

Question 3: If the calculated voltage drop across the collector resistor (V_RC) is greater than the supply voltage (V_CC), the transistor is operating in its active region.

A. Yes

B. No

Explanation: The study materials explicitly state that if the calculated voltage drop across R_C is greater than the supply voltage, the transistor cannot sustain the collector current in the active region and would likely be driven into saturation. For proper amplifier operation in the active region, V_RC must be less than V_CC.

Question 4: Using the revised example where an NPN transistor has a current gain (β) of 100 and a base current (I_B) of 20 µA, what is the calculated collector current (I_C)?

A. 20 mA

B. 0.2 mA

C. 2 mA

D. 200 mA

Explanation: According to the study materials, the collector current (I_C) is calculated using the formula I_C = β · I_B. Given β = 100 and I_B = 20 µA, I_C = 100 · 20 µA = 2000 µA, which is equivalent to 2 mA.

Question 5: The maximum load current (I_C(max)) required for the 12 V, 0.6 W LED strip, as calculated in the example, is 5 mA.

A. Yes

B. No

Explanation: The study material calculates the maximum load current (I_C(max)) for the 12 V, 0.6 W LED strip as Power / Voltage = 0.6 W / 12 V = 0.05 A, which is equal to 50 mA, not 5 mA.