Curie temperature is the temperature that the materials loose their magnetism.In Ni it's 600-650 deg Celcium.The ring is made from Ni-Cr and the rays are from copper. When the system is working less than the Curie temperature the magnet atracts the center and the two sides of the ring (left and right with the same force).So the system doewn't move. When we put a flame , the side near to the flame when we reach the Curie temperature loose it's magnetism so the magnet atracts more the other cold side and the ring moves to the flame.You can see a similar experiment in the net with a pendulum of a 1 Euro coin hung with a copper wire and a small flame and a magnet that make it to do a continuous oscillation.
YOU CAN WATCH THE CONSTRUCTION AND THE USE HERE:
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