EMI Lab (EC-306) - Important Questions

Explain the principle and working of a Wheatstone bridge. Show how to determine the unknown resistance $R_x$ at balance and describe practical procedure, sensitivity, and sources of error.

Describe the Schering bridge and derive the balance conditions for measurement of an unknown capacitor $C_x$ and its loss. Explain experimental steps to determine capacitance and dissipation factor and list common error sources.

Describe the Maxwell (or Maxwell-Wien) bridge used for measurement of an unknown inductance $L_x$ with its series resistance. Derive the balance condition and explain how to obtain $L_x$ and the series resistance experimentally. Discuss limitations of the method.

Using a dual-trace cathode ray oscilloscope (CRO), describe the procedure to measure amplitude, frequency and phase difference between two sinusoidal signals. Include explanation of Lissajous figures for frequency ratio determination and the method to compute phase difference experimentally.

Obtain experimentally the frequency response (magnitude and phase) of a series RC circuit using a function generator and CRO. Plot the Bode magnitude and phase plots and compare with theoretical response. Use the cutoff formula $$f_c = \frac{1}{2\pi\left( R C \right)}$$ in your analysis.

Explain how to measure phase difference between two signals of the same frequency using time-base measurements on a CRO. Show the relation $$\phi = 2\pi f\Delta t$$ and express the phase in degrees. Describe measurement errors and remedies.

Describe the procedure for calibration of a voltmeter and an ammeter by comparison method using standard instruments. Explain sources of systematic error and how calibration certificates/traceability are maintained in laboratory practice.

Explain the use of a strain gauge in a Wheatstone bridge to measure strain. Derive the approximate bridge output voltage for small strain using gauge factor (GF): $$V_{o} \approx \frac{V_{s}}{4}\;\mathrm{GF}\;\epsilon$$ where $V_s$ is the bridge excitation and $\epsilon$ is strain. Describe calibration procedure and typical experimental steps.

Define total harmonic distortion (THD). Describe how to measure THD of a periodic signal using a spectrum analyzer or FFT-capable CRO and give the expression: $$\mathrm{THD} = \frac{\sqrt{\sum_{n=2}^{\infty} V_n^2}}{V_1}\times 100\%\,.$$ Discuss practical considerations in THD measurement.

Describe the operation of a Q-meter and how it is used to determine the resonant frequency and quality factor $Q$ of a tuned circuit. Outline the experimental procedure and factors affecting accuracy.

Describe an experiment to acquire, display and analyze analog signals using a data acquisition (DAQ) system and software (e.g., LabVIEW or Python). Include steps for sampling, anti-aliasing filtering, and verification of results against CRO measurements.