Procedure for real lab
To find mBH
The direction of BH is drawn on the table using a compass needle. The box-type vibration magnetometer is placed with its length parallel to this direction. The bar magnet is then suspended horizontally in the vibration magnetometer with its north pole pointing north. The magnet is set into vibration by momentarily bringing another bar magnet near to it. The time taken for 10 oscillations is determined twice and the mean of t is to be found and period of oscillation (T) can be calculated using equation(2). The mass of the magnet is determined. The length and breadth of the magnet are measured by using vernier calipers. The moment of inertia of the magnet is calculated. From these observations, the value of mBH is calculated using equation(5).
To find m/BH
Tan A position. The compass box alone is rotated so that the (0-0) line is parallel to the arm of the magnetometer. Then the apparatus as a whole is rotated till the aluminum pointer reads (0-0). The bar magnet is placed horizontally, parallel to the arm of the deflection magnetometer, at a distance d from the center of the compass needle, chosen so that the deflection lies between 30° and 60°. The reading of the ends of the pointer are noted. The magnet is then reversed at the same position and the readings of the pointer are again noted. The magnet is then transferred to the other arm of the magnetometer, keeping it at the same distance d, four more deflections are noted as before. The experiment is repeated for different values of d and an average value for m/BH is calculated using equation(7).
Tan B position. The compass box alone is rotated so that the (90-90) line is parallel to the arm of the magnetometer. Then the magnetometer as a whole is rotated so that the pointer reads (0-0). The magnet is placed horizontally, but perpendicular to the arm of magnetometer. Repeat the whole process as before, to get a second average value of m/BH using equation (8), which is combined into an overall average with the first.
To find pole strength P
Tan C position. The compass box alone is rotated so that the (0-0) line is parallel to the arm of the magnetometer. Then the apparatus as a whole is rotated till the aluminum pointer reads (0-0). The magnet is placed vertically on the deflection magnetometer . Repeat the process as before, and calculate the pole strength P using equation (14).
1. Select Vibration Magnetometer for measuring the time period of oscillation of bar magnet.
2. Length of the magnet - Set the horizontal length of the magnet, from 3cm to 7cm.
3. Mass of the magnet - Set the mass of magnet, from 30g to 80g.
4. Breadth of the magnet - Set the horizontal breadth of the magnet, from 1cm to 3cm.
Note: When length and breadth of the bar magnet changes, the correspoding change in the mass is displayed in the simulator part.
5. Place second magnet – Clicking this button starts the oscillation. The Start/Stop button on the timer can then be used to time 10 oscillations, thereby finding a value for T, the period of oscillation.
6. Now, without changing the dimensions of the magnet, click Deflection Magnetometer.
7. Choose the position Tan A, Tan B or Tan C for the deflection magnetometer.
8. Choose the side, A or B, for placing the magnet. For Tan B position, the slider of the rotating angle should be in 90° so that the aluminum pointer reads the value 0-0. For Tan A and Tan C position, there is no need to change the rotating angle.
9. Place the magnet – Clicking this button places the bar magnet on the deflection magnetometer.
10. Distance from the center - Places the magnet a chosen distance d from the center of the compass box. Choose d so that the deflection θ of the aluminum pointer is in the 30°-60°range.
11. Reverse the magnet – Clicking this button reverses the poles of the magnet, to allow noting down the compass box deflection in the opposite direction.
12. Zoom - Using this slider, located at the bottom center of the simulator window, we can read the angle of deflection θ for a particular distance d of the magnet from the center of the compass box.
13. Note down the bar magnet mass M, and dimensions L and b, the various distances d and corresponding deflections θ, for all three of the Tan A, Tan B, and Tan C positions of the bar magnet.
14. Using equations given below, calculate the earth's field horizontal intensity (BH), and the magnetic moment (m) and pole strength (P) of the bar magnet.
15. Reset button – Clicking this button resets the simulator to its default values, but does not change the current choice of deflection or vibration magnetometer.
Observations and calculations
Readings of Vibration magnetometer
Readings of Deflection magnetometer
Pole strength using Tan C position , = ....................A m
1. The horizontal intensity of earth's magnetic field at a place, BH =................... Wbm-2
2. The moment of the bar magnet, m = ...................... Am-2