Atoroidal coil of n turns has a central radius b and a square cross section of side a. find its self-inductance.

Explanation:

As we know that magnetic field due to torroid is given as

this is approximately constant magnetic field along the axis of the torroid

now the flux linked with one coil of the torroid is given as

now total flux of N number of coils is given as

now we know that self inductance is the property of coil in which flux of the coil will link with the current in the coil

So we know that

answer;

d. are made mostly of liquid

explanation;

-the general   composition and structure planets includes; they have a thick gas and liquid layer covering a small,solid core. mostly the gases are hydrogen and helium atmosphere and layers of liquid hydrogen. for instance neptune and uranus are examples of the outer planets, they have a core covered by ice and ammonia.

-neptune's atmosphere is hydrogen and helium with a bit of methane so there is no oxygen to breath and the interior is made up of frozen water and ammonia with a rock and iron core. thus, there is no liquid water or solid surface to survive.