Viva Questions – Conversion of Galvanometer into Voltmeter or Ammeter
Conversion of Galvanometer into Voltmeter or Ammeter – Viva Questions
Experiment Aim
The aim of this experiment is to convert a given galvanometer of known resistance and figure of merit into a voltmeter or an ammeter of desired range and then verify its performance.
Apparatus Used
This experiment uses a moving coil galvanometer, suitable resistances, a battery, a rheostat, a standard voltmeter or ammeter, a plug key, and connecting wires.
Theory-Based Viva Questions
Q1. What is a galvanometer?
A galvanometer detects and measures small electric currents. Therefore, it acts as a highly sensitive electrical instrument.
Q2. Why cannot we use a galvanometer directly as a voltmeter or an ammeter?
A galvanometer carries only a small current safely. Hence, direct use with large current or voltage may damage it.
Q3. What do you mean by the figure of merit of a galvanometer?
The figure of merit represents the current required for unit deflection. Thus, it indicates the sensitivity of the galvanometer.
Q4. How do you convert a galvanometer into a voltmeter?
We connect a high resistance in series with the galvanometer. As a result, the current through it remains within safe limits.
Q5. How do you convert a galvanometer into an ammeter?
We connect a low resistance in parallel with the galvanometer. Consequently, most of the current flows through the shunt.
Q6. Why do we use a high resistance in a voltmeter?
A high resistance ensures negligible current draw. Therefore, the measured potential difference remains accurate.
Q7. Why do we use a shunt resistance in an ammeter?
A shunt provides a low-resistance path. Hence, it protects the galvanometer from excessive current.
Q8. On which factors does the range of a voltmeter depend?
The voltmeter range depends on the series resistance and the galvanometer’s figure of merit.
Q9. On which factors does the range of an ammeter depend?
The ammeter range depends on the shunt resistance and the maximum current capacity of the galvanometer.
Formula-Based Viva Questions
Q10. Write the formula for converting a galvanometer into a voltmeter.
The required series resistance is given by:
R = (V / Ig) − G
Q11. Write the formula for converting a galvanometer into an ammeter.
The shunt resistance is given by:
S = (Ig × G) / (I − Ig)
Procedure-Based Viva Questions
Q12. Why do we verify the converted instrument?
Verification confirms accuracy. Therefore, we compare readings with a standard instrument.
Q13. Why do we use a rheostat in the circuit?
A rheostat allows gradual current variation. Thus, it prevents sudden damage to the galvanometer.
Q14. Why must we ensure tight connections?
Loose connections increase resistance. Hence, they introduce measurement errors.
Errors and Precautions
Q15. State two precautions for this experiment.
Firstly, increase current gradually using a rheostat. Secondly, maintain correct polarity throughout the circuit.
Q16. How does heating affect resistance?
Heating changes resistance values. As a result, the calculated range may become inaccurate.
Result-Based Viva Questions
Q17. What conclusion do you draw if both instruments show nearly equal readings?
Matching readings confirm correct conversion. Thus, the experiment succeeds.
Q18. Why do we connect a voltmeter in parallel?
A voltmeter measures potential difference. Therefore, we connect it across the component.
Q19. Why do we connect an ammeter in series?
An ammeter measures current. Hence, it must lie in the current path.
Application-Based Viva Questions
Q20. Where do we use voltmeters and ammeters?
We use them in laboratories, electrical circuits, electronic devices, and testing systems.
Q21. Why do we not directly use galvanometers as practical meters?
Practical meters need wider range and durability. Therefore, engineers design specialized instruments.
Final Remark
Thus, correct resistance selection and careful verification allow successful conversion of a galvanometer into a voltmeter or an ammeter.
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