Objective
Theory
Galvanometer
Resistance of galvanometer by half deflection method
G – galvanometer resistance for current I
θ – galvanometer deflection for current I
k – proportionality constant.
Figure of merit of a galvanometer
Learning Outcomes
Students understand the various components used in the experiment.Students learn the concept, ‘figure of merit’.Students are able to construct circuits based on circuit diagrams.
Procedure :
Materials Required
A weston type galvanometerA battery or battery eliminatorTwo resistance boxesTwo one-way keysConnecting wires
Real Lab Procedure
Resistance of galvanometer by half deflection method :
Arrange the components on a table and connect them as per the circuit diagram.Make sure that plugs of the resistance boxes are tight.Take out a high resistance from the resistance box 1 and insert the key k1.Adjust the resistance from this resistance box to get maximum galvanometer deflection.Note the deflection and record it as θ in the tubular column.Insert the key k2 also, without changing the value on the resistance box.Now, adjust the resistance from the low resistance box such that galvanometer shows deflection which is exactly half of the previous reading.Record the value of low resistance box.We can repeat the experiment by changing the value of high resistance R and adjusting low resistance S.The resistance of the given galvanometer can be calculated each time by using the relation G= RS/(R-S).
Figure of merit of the galvanometer :
Release key k2 from the connection. Insert key k1.Adjust the value of R such that the galvanometer shows a certain deflection.Record the observations in a tabular column.Repeat the experiment by changing the value of R and note the galvanometer deflection each time.We can find the figure of merit of the galvanometer by using the equation, k= E/(R+G)θ.
Simulator Procedure (as performed through the Online Labs)
Select the ‘Galvanometer’ form the drop down list.To see the circuit diagram, click on the ‘Show circuit diagram’ check box seen inside the simulator window.Connections can be made as seen in the circuit diagram by clicking and dragging the mouse from one connecting terminal to the other connecting terminal of the devices to be connected.Once all connections are made, click and drag key 1 to insert it into the switch.You can select the desired large resistance from the resistance box.The galvanometer shows a deflection.Now click and drag key 2 to insert it into the switch without changing the value of the resistance.Select the resistance from the small resistance box such that the galvanometer shows deflection which is exactly half of the previous reading.To see the result, click on the ‘Show result’ check box.To redo the experiment, click on the ‘Reset’ button.
Observations
Resistance of the galvanometer by half deflection method.
No. |
Resistance, R
()
|
Deflection in the
galvanometer,
|
Shunt Resistance, S
()
|
Half deflection,
|
Galvanometer
resistance
()
|
1 | Figure of Merit of a Galvanometer:3.63636 *10-5 Ωm | ||||
Figure of merit of the galvanometer
No. |
Resistance, R
()
|
Deflection,
(div.)
|
Figure of Merit,
( Amp/div )
|
Figure of Merit of a Galvanometer:3.63636 *10-5 Ωm | |||
Calculations
Results
The figure of merit of the given galvanometer, k =———- Amp / div.
1) | Why a moving coil galvanometer is called so? | |||||
None of these
Because the coil moves while the magnet remains fixed.
Because the number of turns of the coil varies with current.
Because the coil moves along with the magnet.
|
2) | How can you increase the sensitivity of a moving coil galvanometer? | |||||
By increasing the area of the coil
Both a and c
By increasing the number of turns of the coil
By decreasing the number of turns of the coil
|
3) | What is meant by the figure of merit of a galvanometer? | |||||
Voltage required to produce unit deflection on the galvanometer
Maximum deflection on the galvanometer
None of these
Current required to produce unit deflection on the galvanometer
|
4) | If the current through a galvanometer is, I = Kθ/NAB, then what is the sensitivity of the galvanometer? | |||||
None of these
S = NAB/Kθ
S = K/NAB
S = NAB/K
|
5) | What is the unit of figure of merit of a galvanometer? | |||||
Ampere
Ampere per meter
Ampere per division
Volt
|
6) | Choose the incorrect statement from the following. | |||||
The resistance of the coil of the galvanometer is called the resistance of the galvanometer.
Figure of merit of a galvanometer is the reciprocal of current sensitivity.
Galvanometer has positive and negative terminals.
Galvanometer deflection is proportional to the amount of current passed through it.
|
7) | What is the figure of merit of the galvanometer if current I produce a deflection θ in it? | |||||
I^2/θ
Iθ
I/2θ
I/θ
|
8) | A resistance of 900Ω is connected in series with a galvanometer of resistance 100Ω. A potential difference of 1 V produces 100 division deflections in the galvanometer. Find the figure of merit of the galvanometer? | |||||
2×10^-5 A/div.
0.5×10^-5 A/div.
10^-5 A/div.
10^-6 A/div.
|
Books
Websites
http://www.vbpsnoida.com/student/Worksheets/Moving%20coil%20galv.pdfhttps://www.youtube.com/watch?v=9f6K7NgX9x0http://www.citycollegiate.com/galvanometer_XIIb.htmhttp://notes.tyrocity.com/moving-coil-galvanometer/https://books.google.co.in/books?isbn=8131803848https://books.google.co.in/books?isbn=8173352275
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Department Of Electronics & Information Technology
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