Basic Electronic Circuits and Measurements
What this domain tests
Basic Electronic Circuits and Measurements covers rectifier and amplifier building blocks and the instruments used to check them: multimeter, CRO/oscilloscope, signal generator and breadboard. Expect meter-connection, CRO scaling and waveform-frequency questions.
Core rules
- An ammeter goes in series and has low resistance; a voltmeter goes in parallel and has high resistance. An ohmmeter is used only on a de-energised circuit.
- A CRO display: peak-to-peak voltage = vertical divisions × volts/div × probe attenuation. Period = horizontal divisions for one cycle × time/div; frequency f = 1/T.
- AC coupling blocks DC and shows only the AC component; DC coupling shows both.
- For a 50 Hz input, a half-wave rectifier gives 50 Hz ripple; a full-wave or bridge rectifier gives 100 Hz ripple.
- A bridge rectifier needs four diodes; the output ripple frequency is twice the input frequency.
Worked example
A CRO set to 2 V/div and 0.5 ms/div shows a sine wave 3 divisions high peak-to-peak and one cycle occupying 4 horizontal divisions. With a ×10 probe, Vpp = 3 × 2 × 10 = 60 Vpp. Period T = 4 × 0.5 ms = 2 ms, so f = 1/0.002 = 500 Hz. The peak voltage is 30 V, because Vpp = 2 × Vpeak.
Traps
Calling the 3-division height the peak instead of peak-to-peak; forgetting the ×10 probe; measuring resistance with power on; and placing an ammeter across a supply, which acts almost as a short circuit. Also check whether a meter displays RMS or peak; they differ by √2 for a sine wave.