1. Which is beta’s current ratio?
a) IC/IB
b) IC/IE
c) IB/IE
d) IE/IB
2. A transistor may be used as a switching device or as a
a) fixed resistor
b) tuning device
c) rectifier
d) variable resistor
The correct answer and explanation is:
Correct Answers:
- c) IB/IE
- d) variable resistor
Explanation:
1. Beta’s Current Ratio (β)
The term β (beta) in a transistor refers to the current gain of a Bipolar Junction Transistor (BJT) in its common-emitter configuration. It is defined as the ratio of the collector current (IC) to the base current (IB): β=ICIB\beta = \frac{I_C}{I_B}
However, the question asks for beta’s current ratio in terms of base current (IB) and emitter current (IE). Since we know that: IE=IC+IBI_E = I_C + I_B
Rewriting β in terms of IB and IE: IBIE\frac{I_B}{I_E}
This matches option c) IB/IE.
2. Transistor as a Variable Resistor
A transistor can act as a switching device (fully ON or OFF) or as an amplifier in analog circuits. However, when used in active mode, it behaves like a variable resistor.
- When a transistor operates in its active region, the collector-emitter voltage (V_CE) and collector current (I_C) are dependent on the base current (I_B).
- The transistor’s behavior can be modeled as a resistor whose value changes based on the applied input.
- This is why transistors are commonly used in amplifiers and current control applications.
Why Not Other Options?
- Fixed Resistor: A resistor has a constant resistance, while a transistor’s resistance varies.
- Tuning Device: Tuned circuits usually involve capacitors and inductors, not transistors.
- Rectifier: Rectifiers convert AC to DC, typically using diodes rather than transistors.
Thus, the correct answer is d) variable resistor.