CABT Fundamentals of Electronics 2 — Questions and Answers
Question 1: A capacitor is connected in series with a resistor to an AC source. As frequency increases, what happens to the capacitive reactance (Xc)?
- Xc increases
- Xc decreases (Correct answer)
- Xc remains constant
- Xc becomes zero
Correct answer: Xc decreases
Capacitive reactance Xc = 1/(2πfC), so as frequency increases, Xc decreases.
Question 2: In a biomedical device, a zener diode is used primarily to:
- Amplify small signals
- Regulate voltage (Correct answer)
- Rectify AC to DC
- Store electrical charge
Correct answer: Regulate voltage
Zener diodes operate in reverse breakdown to maintain a stable reference voltage, making them ideal for voltage regulation.
Question 3: What is the time constant (τ) of an RC circuit with R = 10 kΩ and C = 100 µF?
- 0.1 seconds
- 1 second (Correct answer)
- 10 seconds
- 100 seconds
Correct answer: 1 second
τ = RC = 10,000 Ω × 0.0001 F = 1 second.
Question 4: Which type of amplifier configuration provides both voltage gain and current gain but with a 180° phase shift?
- Common base
- Common collector
- Common emitter (Correct answer)
- Common gate
Correct answer: Common emitter
The common emitter configuration inverts the output signal (180° phase shift) and provides both voltage and current gain.
Question 5: In an ECG machine, the CMRR (Common Mode Rejection Ratio) specification is important because it:
- Increases signal amplitude
- Rejects 60 Hz power line interference (Correct answer)
- Filters high-frequency noise
- Amplifies differential signals only
Correct answer: Rejects 60 Hz power line interference
High CMRR allows the differential amplifier to reject common-mode noise such as 60 Hz interference from power lines while amplifying the ECG signal.
Question 6: What is the function of a low-pass filter in biomedical signal processing?
- Passes high frequencies and attenuates low frequencies
- Passes low frequencies and attenuates high frequencies (Correct answer)
- Passes a specific band of frequencies
- Attenuates all frequencies equally
Correct answer: Passes low frequencies and attenuates high frequencies
A low-pass filter allows signals below its cutoff frequency to pass while attenuating higher frequency components.
Question 7: An op-amp in an inverting configuration has Rf = 100 kΩ and Rin = 10 kΩ. What is the voltage gain?
- +10
- -10 (Correct answer)
- +0.1
- -0.1
Correct answer: -10
Inverting amplifier gain = -Rf/Rin = -100kΩ/10kΩ = -10, where the negative sign indicates phase inversion.
CABT Fundamentals of Electronics 2
A capacitor is connected in series with a resistor to an AC source.
As frequency increases, what happens to the capacitive reactance (Xc)?