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Effects and applications of electric currents 635 Effects of an electric current 636 Heating effect of a current 636 Chemical effect of a current 637 Magnetic effect of a current 638 Theory of magnetism 638 Electromagnetism 640 Solenoids and electromagnets 641 Electromagnetic switches (relays) 643 Electrical measuring instruments 644 Electromagnetic induction 645 Electric motors 648 Direct and alternating current 649 Technical terms 649 Review questions 649