ISCET Electronic Components & Circuit Analysis 5 — Questions and Answers
Question 1: What is the primary difference between a JFETand a MOSFET?
- JFETs can handle higher voltages
- MOSFETs have an insulated gate that draws virtually no gate current (Correct answer)
- JFETs are faster switching devices
- MOSFETs require a junction to operate
Correct answer: MOSFETs have an insulated gate that draws virtually no gate current
MOSFETs have a metal-oxide insulating layer between the gate and channel, resulting in extremely high gate input impedance and negligible gate current.
Question 2: A transformer has 500 primary turns and 50 secondary turns. If the primary voltage is 120 V, what is the secondary voltage?
- 1200 V
- 120 V
- 12 V (Correct answer)
- 6 V
Correct answer: 12 V
Turns ratio Ns/Np = Vs/Vp → Vs = 120 × (50/500) = 12 V; this is a 10:1 step-down transformer.
Question 3: In a series RLC circuit at resonance, which statement is true?
- Inductive reactance is greater than capacitive reactance
- Impedance is at its maximum value
- Circuit current is at its minimum value
- Inductive and capacitive reactances are equal and cancel (Correct answer)
Correct answer: Inductive and capacitive reactances are equal and cancel
At resonance, XL = XC, so they cancel and the total impedance equals only the resistance R, maximizing current.
Question 4: The term 'breakdown voltage' for a capacitor refers to:
- The voltage at which the capacitor is fully charged
- The maximum voltage before the dielectric fails (Correct answer)
- The DC working voltage rating
- The peak ripple voltage the capacitor can handle
Correct answer: The maximum voltage before the dielectric fails
Breakdown voltage is the voltage at which the dielectric material permanently fails, allowing current to flow through the capacitor.
Question 5: What is the output waveform of a half-wave rectifier fed with a 60 Hz sine wave?
- A 60 Hz square wave
- Pulsating DC at 60 Hz (Correct answer)
- Pulsating DC at 120 Hz
- A pure DC voltage
Correct answer: Pulsating DC at 60 Hz
A half-wave rectifier passes only one half-cycle per input cycle, producing pulsating DC at the same frequency as the input (60 Hz).
Question 6: In a voltage divider circuit with R1 = 10 kΩ (top) and R2 = 5 kΩ (bottom) connected to 15 V, what is the output voltage across R2?
- 10 V
- 7.5 V
- 5 V (Correct answer)
- 3.75 V
Correct answer: 5 V
Vout = Vin × R2/(R1+R2) = 15 × 5k/(10k+5k) = 15 × 1/3 = 5 V.
Question 7: What does a negative temperature coefficient (NTC) thermistor do as temperature increases?
- Resistance increases proportionally
- Resistance remains constant
- Resistance decreases (Correct answer)
- Resistance increases exponentially
Correct answer: Resistance decreases
NTC thermistors decrease in resistance as temperature rises, making them useful for temperature sensing and inrush current limiting.
ISCET Electronic Components & Circuit Analysis 5
What is the primary difference between a JFETand a MOSFET?