In order to produce a planet-wide magnetic field, a planet must have in its interior some material capable of carrying the electric current in such a way as to produce a dynamo effect. All of the following substances appear to be able to fill this role, except one. Which is the exception?
A)molten iron
B)solid iron
C)liquid metallic hydrogen
D)a liquid water-ammonia mixture under high pressure

Question

Quizplus · Accepted Answer

Solid iron cannot carry an electric current in a manner that would produce a dynamo effect necessary for generating a planet-wide magnetic field. The dynamo effect requires fluid motion within the planet's interior, which is possible with molten iron, liquid metallic hydrogen, and high-pressure liquid water-ammonia mixtures, but not with solid iron.

In Order to Produce a Planet-Wide Magnetic Field, a Planet