Can someone explain what is referred by the cross sectional area of a solenoid? Would this be the same for an air solenoid vs a solenoid with a core vs a solenoid with a hollow core?

A- a of 8.00 cm a of 34.0 nc. a , -, a of 25.0 nc is on of a of 15.0 cm .be toto aof ? a) b) c) j d) e)

You are given a vector a = 125i and an unknown vector b that is perpendicular to a. the cross-product of these two vectors is a × b = 98k. what is the y-component of vector b?

The sun’s mass is 2.0×10^ 30 kg, its radius is 7.0×10 5 km, and it has a rotational period of approximately 28 days. if the sun should collapse into a white dwarf of radius 3.5×10 3 km, what would its period be if no mass were ejected and a sphere of uniform density can model the sun both before and after?