physics

The magnetic flux density B in a long solenoid is given by:

B = u.n.I
where u is the permeability of the core material
n is the no. of turns of the coil per unit length
I is the current flowing through the coil of the solenoid

It is thus apparent that statements (1) and (2) are correct.
The answer is therefore option B

2011-06-01 15:43:03 補充：
Please refer to the following web-page for explanation of the equation:
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html#c1