An engineer needs to demagnetise a steel bar. She places the bar inside a solenoid and then slowly removes it while the power supply is switched on.
Which combination of power supply type and explanation describes the most effective method for demagnetising the bar?
d.c. supply: A constant magnetic field is needed to randomise the orientation of the magnetic domains.
a.c. supply: The alternating magnetic field repeatedly reverses the magnetic domains, and slowly removing the bar reduces this effect to zero, leaving them randomised.
d.c. supply: A strong constant magnetic field permanently aligns the domains in a closed-loop pattern.
a.c. supply: The alternating current heats the bar up to its Curie temperature, which destroys the magnetism.
169 exam-style questions on CIE IGCSE Physics Simple phenomena of magnetism, covering Simple phenomena of magnetism. Each one has a worked solution and a mark scheme showing where the marks go.