(https://physicscup.ee/)
Physics Cup – TalTech 2022 – Problem 1
By Jaan Kalda (TalTech).
= 1cm is made from a NdFeB alloy. The figure below shows the left upper
< 0, B > 0) of the hysteresis loop of this alloy for two temperatures, T1 = 20∘ C, and T2 =
A spherical ball of radius R
quadrant (H
​
​
120∘ C . Initially, the ball has been magnetized by putting it into a very strong homogeneous magnetic field
(with B ≈ 3T). Then, the external magnetic field is removed while the temperature of the ball is kept equal
to T1 = 20∘ C . After that, the ball is heated up to the temperature T2 = 120∘ C . By how much did the
​
​
magnetic dipole moment of the ball change due to heating?
Please submit the solution of this problem via e-mail to physcs.cup@gmail.com.
(mailto:physcs.cup@gmail.com?subject=Problem No 1) First hints will appear here on 28th November 2021
or on 5th December, depending on the number of correct solutions submitted during the first week. After
the publication of the first hint, the base score is reduced to 0.9 pts. For full regulations, see the
“Participate” tab (https://physicscup.ee/participate/). The intermediate results for the Problem 1 will be
drawn after 13:00 GMT, 28th November 2021.