Physics Paper 5 : Sample Solution

Q) The Properties of many magnetic materials are affected by temperature. One effect is the loss of permanent magnetism when the temperature of the magnetic material exceeds a particular value. This Temperature is known as the Curie Point.

Design an experiment to investigate how the magnetic field strength of a magnet depends on the temperature of the magnet in the range from 0-200 degree Celsius. (May/June 2002)

Sol:-

Apparatus:
1)Tongs
2) Rubber gloves and protective goggles
3) engine oil ( boiling point > 250 degree celsius)
4) Digital Thermometer
5) Calibrated Hall Probe with Tesla Meter and a permanent steel magnet
6) Trough
7) Electric Heater with thermostat
8) Dry ice and an insulated container for its storage

Variables:
Independent: Temperature would be the independent variable since its effect on magnetic flux density need to be observed and will be changed by the observer.
Dependent: Flux density
Control: To ensure a fair test, make sure no other magnetic material is near the apparatus setup; Carry out the experiment at room temperature. Also the distance of hall probe should be constant from the magnet, otherwise different values would be obtained for the same temperature and fair test cannot be ensured.

Procedure :
Fill the trough with engine oil and insert the probe/sensor of digital thermometer in it. First add dry ice and let the temperature fall to 0 degree celsius. Now immerse the permanent steel magnet inside the oil and allow it to remain in for 10 minutes. Add the dry ice after every 2-3 minutes to ensure the temperature is maintained at 0. After the time period , take out the magnet with tongs and position the hall probe w/ tesla meter such that it is normal to magnetic flux. Record the value of flux density obtained and repeat the procedure for the same temperature. Now turn on the electric heat and maintain temperature at 50 degree C. Immerse the magnet, repeat the same procedure and calculate the value of flux density obtained. Repeat it for temperatures of 100, 150 and 200 degree C besides that for 0 and 50 which has already been done.

Tabulate the results obtained :
Temperature/*C (Flux Density/T)1 (Flux Density/T)2 (Flux Density/T)Avg
0
50
100
150
200

Draw a graph of Flux Density ( Y-axis) against Temperature( X-axis)
Observe the general trend of the plotted line. If a general decreasing trend is obtained , preferably linear such that it meets the x-axis at a specific point (Curie point) , the relationship is proved.

Improvements and Safety Concerns
Always wear the protective goggles and rubber gloves to prevent damage in case the bubbling oil spills. Handle the magnet with tongs due to temperature extremities.
Allow magnet to reach thermal equilibrium ( which is why it is kept in a steady temp for some time) to ensure uniform temperature distribution. Only then measure the flux density with hall probe.
As stated above perform the experiment away from any magnetic material that might distort the values for flux density.