CABT Fundamentals of Electronics 5 — Questions and Answers
Question 1: What type of feedback is used in most biomedical amplifier designs to stabilize gain and improve linearity?
- Positive feedback
- Negative feedback (Correct answer)
- Regenerative feedback
- No feedback
Correct answer: Negative feedback
Negative feedback reduces gain but improves stability, linearity, bandwidth, and reduces distortion — essential characteristics for accurate biomedical signal amplification.
Question 2: A defibrillator capacitor stores 360 joules at 5000 V. What is the capacitance value?
- 14.4 µF
- 28.8 µF (Correct answer)
- 72 µF
- 144 µF
Correct answer: 28.8 µF
Energy E = ½CV², so C = 2E/V² = 2×360/(5000²) = 28.8 µF.
Question 3: In a pulse oximeter, photodetectors measure light absorption at two wavelengths. Which wavelengths are typically used?
- 450 nm and 550 nm
- 660 nm and 940 nm (Correct answer)
- 750 nm and 850 nm
- 500 nm and 700 nm
Correct answer: 660 nm and 940 nm
Pulse oximeters use red light (~660 nm) and infrared light (~940 nm) because oxyhemoglobin and deoxyhemoglobin have distinct absorption differences at these wavelengths.
Question 4: What is the Nyquist theorem's requirement for sampling an analog signal to avoid aliasing?
- Sample at the same rate as the signal frequency
- Sample at least twice the highest frequency in the signal (Correct answer)
- Sample at least 10 times the signal frequency
- Sample at the signal's fundamental frequency
Correct answer: Sample at least twice the highest frequency in the signal
The Nyquist theorem states that the sampling rate must be at least twice the highest frequency component of the signal to accurately reconstruct it without aliasing.
Question 5: In a biomedical pressure transducer using a strain gauge, what electrical parameter changes in response to physical deformation?
- Capacitance
- Inductance
- Resistance (Correct answer)
- Voltage
Correct answer: Resistance
Strain gauges work on the piezoresistive principle — mechanical deformation changes the geometry of the conductor, altering its electrical resistance.
Question 6: What is the function of a sample-and-hold circuit in an analog-to-digital conversion system?
- Amplifies the analog signal before conversion
- Freezes the analog signal value during the ADC conversion period (Correct answer)
- Filters noise from the analog signal
- Converts digital output back to analog
Correct answer: Freezes the analog signal value during the ADC conversion period
A sample-and-hold circuit captures and maintains the analog input voltage constant during the ADC's conversion time, preventing errors from signal changes during conversion.
Question 7: In medical electronics, what is the maximum allowable patient leakage current for a Type CF (cardiac floating) applied part under normal conditions per IEC 60601-1?
- 10 µA (Correct answer)
- 100 µA
- 500 µA
- 1000 µA
Correct answer: 10 µA
IEC 60601-1 limits patient leakage current for Type CF (cardiac floating) applied parts to 10 µA under normal conditions to protect against microshock hazards.
CABT Fundamentals of Electronics 5
What type of feedback is used in most biomedical amplifier designs to stabilize gain and improve linearity?