Table of Contents
Objective:
To determine the resistance of a galvanometer by half deflection method and to find its figure of merit.
Apparatus Required:
A Weston type galvanometer, a voltmeter, a battery or
battery eliminator, two(10000 ohm and 1000 ohm) resistance boxes, two one-way keys, a rheostat, a screw gauge, a metre scale, an ammeter if given range,
connecting wires and a piece of sand paper.
Formula Used:
a) To find the resistance of galvanometer:
Where,
G is the resistance of the galvanometer
R is the resistance of the resistance box.
S is the shunt resistance.
b) To find the figure of merit:
The figure of merit is current per unit deflection.
Where,
I is the current in the circuit.
k is the figure of merit.
θ is the deflection.
E is the e.m.f. of the cell or battery eliminator.
Circuit Diagram:
Observations :
(a) Resistance of galvanometer by half deflection method:
(b) The figure of merit:
Least count of voltmeter = 0.01 V
Range of voltmeter = 0-20 V
Zero error of voltmeter = nil
Calculations :
a) Resistance of Galvanometer
b) Figure of merit
Result:
Resistance of given Galvanometer, G = 55.43 Ω
Figure of merit of Given Galvanometer, k= 6.25 x 10¯5 A/div
Precautions:
1. All connections must be neat and tight.
2. Key Kl should be closed after taking out a high resistance from the
resistance box R.
3. The deflection of galvanometer should be large.
4. The emf of cell or battery should be constant.
5. All the plugs in resistance boxes should be tight.
Sources Of Error:
1. The screws of the instruments may be loose.
2. The plugs of resistance boxes may not be clean.
3. The emf of battery may not be constant.
4. The galvanometer divisions may not be of equal size.
Viva Questions
Q.1. Name two devices used for measuring potential difference between two points in an electric field.
Ans. Potentiometer and voltmeter.
Q.2. How do you determine the resistance of the galvanometer?
Ans. By half deflection method.
Q.3. What do you understand by resistance of a galvanometer and can it be determined?
Ans. It is the resistance offered by the coil of the galvanometer to the flow of current through it. It can be found by half deflection method.
Q.4. Which method is being used by The half deflection method. you to determine the resistance of galvanometer?
Ans. The half deflection method.
Q.5. Define current sensitivity of a galvanometer.
Ans. The deflection produced in the galvanometer, when unit current is passed through it, is called current sensitivity of the galvanometer.
Q.6. Why galvanometer is called a moving coil galvanometer?
Ans. In this galvanometer, the coil moves, while the magnet remains fixed.
Q.7. Which part of galvanometer offers resistance?
Ans. Coil of the galvanometer.
Discover more from EduGrown School
Subscribe to get the latest posts sent to your email.
