SPECIAL LABORATORY PRACTICUM IN THE DISTANCE FORM OF EDUCATION

Abstract

The article proposes the methodology of laboratory work of the special workshop of the 4th year at the distance form of education on the example of laboratory work ‘Determination of Curie temperature from the temperature dependence of heat capacity of ferromagnets’. At the distance form of education there is no possibility to carry out a physical experiment, so it is proposed to expand the range of calculation-graphic tasks for the laboratory work. Students are given a ready-made table of experimental data, in this case, the table of heat capacity of nickel for the temperature range 1÷1500 K.

In the course of the work, students, using the experimental data obtained for the heat capacity of nickel, should plot the dependence of C_V on temperature, calculate the lattice contribution to the total heat capacity using the Debye model, and calculate the electronic and magnetic components of the heat capacity. Students find the Debye temperature θ_D and the electronic heat capacity coefficient γ necessary for the calculation from the condition that at very low temperatures the magnetic component of the heat capacity can be neglected and the lattice component of the heat capacity is approximated by a cubic dependence on temperature. 

The Curie point is the point of phase transition of the second kind, in the vicinity of which specific anomalies are observed. According to the similarity theory, the singular part of the heat capacity is characterized by the following relations:

C(t)=(A^±⁄α^± )(t ^-α± -1)+B^± (±), where A^-, B^-, A⁺, B⁺ are constants, α^-  and α⁺ are critical indices, t=(T-T_k )⁄T_k . Differentiating and logarithmising these relations, we can obtain equations that allow us to determine the critical indices (log|(dC_m)/dT|=-(α^±+1)  log|T-T_c |+D). Since the experimental value of the Curie temperature was given to an accuracy of ± 1 K, students should plot a series of graphs log|(dC_m)/dT| from log|T-T_c | for different T_c (from 624.4 K to 628 K through 0.4 K). From the tangent of the slope of the obtained straight lines, the critical exponent for a given Curie temperature is determined. According to the theory of similarity, the critical indexes should be equal. Therefore, from the intersection of the curves α^- (T) and α⁺ (T), the true values of the critical index and the Curie temperature can be determined.