To find the resistance of galvanometer by half deflection method.

 

Abstract:

In this experiment, we determine the resistance of a galvanometer using the half deflection method. This method involves passing known currents through the galvanometer and measuring the corresponding deflections on the scale. By applying the principle of balancing the galvanometer's deflection, we can calculate its resistance.

Introduction:

The half deflection method is a technique used to find the resistance of a galvanometer without using a separate resistance box. It is based on the principle that when half the full-scale deflection current flows through the galvanometer, the shunt resistance connected in parallel to the galvanometer balances the current effectively. This allows us to determine the resistance of the galvanometer using simple circuit calculations.

Experiment Details:

The experiment setup includes a galvanometer, a variable resistor (rheostat), a battery, an ammeter, and connecting wires.

Procedure:

1. Set up the circuit as shown in the diagram, with the galvanometer connected in series with the variable resistor (rheostat) and the battery.
2. Adjust the rheostat until the galvanometer shows half of its full-scale deflection.
3. Measure the current passing through the circuit using the ammeter. Let it be I_G.
4. Record the resistance of the rheostat as R.

Observations and Calculations:

The current passing through the galvanometer, I_G, is given by:

\( I_G = \frac{V}{R} \)

Where V is the potential difference across the galvanometer and R is the total resistance of the circuit.

From the experiment, we know that when the galvanometer shows half-scale deflection, the current through it is half the full-scale deflection current. Hence, \( I_G = \frac{I}{2} \).

Equating these two expressions, we can find the resistance of the galvanometer, \( R_G \).

Finally, the resistance of the galvanometer is given by:

\( R_G = \frac{V}{I/2} \)

Conclusion:

Through the half deflection method, we successfully determined the resistance of the galvanometer. This method provides a simple yet effective way of finding the galvanometer resistance without the need for additional equipment.

Precautions:

• Ensure all connections are secure and proper.
• Handle the equipment with care to avoid damage.
• Take accurate readings to ensure precise results.

Short Questions with Answers:

1. Q: What is a galvanometer?
   A: A galvanometer is an instrument used for detecting and measuring electric current.
2. Q: What is the principle of the half deflection method?
   A: The principle of the half deflection method states that when half the full-scale deflection current flows through a galvanometer, the shunt resistance connected in parallel balances the current effectively.
3. Q: Why is the rheostat adjusted in the half deflection method?
   A: The rheostat is adjusted to control the current passing through the galvanometer until it shows half of its full-scale deflection.
4. Q: What is the significance of half-scale deflection in the half deflection method?
   A: Half-scale deflection ensures that the current passing through the galvanometer is balanced, simplifying the calculation of its resistance.
5. Q: How is the resistance of the galvanometer calculated in the half deflection method?
   A: The resistance of the galvanometer is calculated using the formula: \( R_G = \frac{V}{I/2} \), where \( V \) is the potential difference across the galvanometer and \( I \) is the current passing through it.

Multiple Choice Questions (MCQs):

1. What method is used to find the resistance of a galvanometer?
• a) Full Deflection Method
• b) Half Deflection Method
• c) Quarter Deflection Method
• d) None of the above

Correct Answer: b) Half Deflection Method
2. What is adjusted until the galvanometer shows half-scale deflection?
• a) Ammeter
• b) Rheostat
• c) Voltmeter
• d) None of the above

Correct Answer: b) Rheostat
3. Which principle does the half deflection method rely on?
• a) Ohm's Law
• b) Faraday's Law
• c) Balancing Principle
• d) Newton's Law

Correct Answer: c) Balancing Principle
4. What does adjusting the rheostat achieve in the half deflection method?
• a) It changes the resistance of the galvanometer
• b) It balances the current passing through the galvanometer
• c) It increases the voltage across the galvanometer
• d) None of the above

Correct Answer: b) It balances the current passing through the galvanometer
5. Why is it important for the galvanometer to show half-scale deflection in the half deflection method?
• a) It ensures the accuracy of the experiment
• b) It simplifies the calculations
• c) It avoids damage to the galvanometer
• d) All of the above

Correct Answer: d) All of the above