A glass tube 1 m long and 2cm diameter is completely and uniformly wound with 900 turns of copper wire 0.9 mm diameter insulated to 1mm diameter....



A long wire wrapped around in a coil of loops
of wire is called a solenoid.  To calculate the magnetic field in a solenoid one needs
to apply Ampere's Law which provides this equation:

B = UIN  where U
is the permeability, I is the current in the wire and N is the number of coils (or
"turns of wire").

U is a constant equal to 4 Pi X10^-7
Tm/A

N is 900 for this
problem.

I needs to be calculated using Ohm's
Law

I = V/R

R is not given
directly, however we can calculate the length of the wire by multiplying the
circuference of one loop by the number of loops.  In meters, the length will be Pi X D X
N = Pi X 0.02 m X900 = 56.5 meters.

The resistance of the
wire can be determined by multiplying the length of the wire by the linear resistance
which in meters is 0.172 Ohms/meter.

Therefore R = 0.172
Ohms/m X 56.5 m = 9.73 Ohms

I = 4.0 V/9.73 Ohms = 0.411
Amps

This gives us the information to calculate the
magnetic field strength inside the solenoid:

B = 4Pi X
10^-7T m/A X 0.411A X 900 turns/m =  4.65 X 10^-4 T