Apparatus:
Stewart and gee’s type galvanometer, batter, ammeter, rheostat, one way plug key, reversing Ley connecting wires and sand paper,
Stewart and Gee’s tangent galvanometer
It consist of a circular coil of several turns of thin undulated copper wire wound on a wooden Game and fixed on a horizontal base with its plane vertical. The free ends of the wire of the coil are connected to terminalt and t provided at the base. A deflection magnetometer is along the horizontal direction with the center of needle always lies on the axis of the coil. The magnetometer arms carry scales on which the distance of the needle from the center of the coil can be read with the help of the index attached to this sliding base on the magnetometer.
the magnetic field B produced by a circular coil of radius r at a distance x from the center of the coil when current I is passing through its n turn is given by
Where is the deflection of the magnetometer.
This show that a graph between tan and x is similar to the graph between b and x.
Procedure:
1. Arrange the apparatus such that the magnetometers arm are roughly east and west, and the needle lies at the center of the circular coil.
2. Set the coil with its plane vertical and parallel to the magnetic meridian with the help of the needle of the magnetometer. Rotate the compass box such that the pointer lies at the 0-0 line
3. Make the connection as shown in the circuit diagram
4. Adjust the current in the coil with rheostat to give deflection of about 75oWhen magnetic needle lies exactly in the plane of the coil. Keep the current diagram
5. Reverse the direction of the current flowing in the coil and note the deflection in reversed direction. The two deflection must be same if not adjust the position of the apparatus till the two deflection become equal.
6. Now slide the magnetometer box along the axis and obtain the position of maximum deflection in this position, the center of the needle coin slide with the center of the coil.
7. Note the position, on the scale fixed to the arms of the magnetometer against the index P1 and read both ends of the pointer attached to the needle. Reverse the current and again read both ends.
8. Shift the magnetometer box along the axis by steps of 2 cm and note the reading of the magnetometer at each distance. Continue this shift of magnetometer as far as the apparatus permits or until the deflection is reduced to 10°
9. Repeat the observation on the other side of the coil keeping the current constant all the time.
10. Plot a graph between tan and x for each side which shows how the magnetic field varies with x along the axis of the coil. Also measure the distance between the points of inflexion at c and d.
Observation & calculations
Result
From graph the distance between the points of inflection c and d is approximately equal to the radius of the coil.
Precautions:
1. Remove all magnets, magnetic substance from the neighborhood of the apparatus.
2. The current should remain constant during the experiment.
3. Avoid parallax between the needle and its image while taking reading.
Viva voce
Q.1: What is the unit of magnetic field?
Ans: tesla (T) is the unit of magnetic field. A smaller unit g gauss is also used.
Q.2: How does a current carrying circular loop (coil) behave?
Ans: It behaves like a magnet with one face as north pole and other south pole.
Q.3: What is meant by point of inflexion?
Ans: it is the point where curvature of the curve changes.
Q.4: Why magnetic needle used in the compass?
Ans: Because its ends always set along north and sound.
