What is the mangitude field inside the inner solenoid?

[jersey]

Homework Statement

1. Homework Statement


A 20cm long solenoid has 4000 turns of wire. Insiude this solenoid is a second on, also 20cmlong but with 2500 turns of wire. If a 2.5 A current flows in each solenoid in the same directon, what is the magnetic field inside the inner solenoid?

2. Homework Equations

See below.

3. The Attempt at a Solution

magnetic field = permeability x turn density x current

For a solenoid of length L 20cm with N = 2500 turns , the turn density is n= N/L = 125 turns/ m.
I=2.5 ampres.

B =0.07853981633974483 Tesla

Is this correct?

Does the Does the fact that it is one inside the other affect my calculations?
]

 

[granpa]

the field inside the inner coil is simply the sum of the field due to the inner coil plus the field due to the outer coil

 

[jersey]

So I have:
magnetic field = permeability x turn density x current

For a solenoid of length L 20cm with N = 2500 turns , the turn density is n= N/L = 125 turns/ m.
I=2.5 ampres.

B =0.07853981633974483 Tesla

+

magnetic field = permeability x turn density x current

For a solenoid of length L 20cm with N = 4000 turns , the turn density is n= N/L = 200 turns/ m.
I=2.5 ampres.

B = Tesla

argh! what am i not getting?

 

[granpa]

mixing cm with m

 

[jersey]

.20 should be used not 20.

What about my second equation, can you help me substitute in?

 

[jersey]

Can anyone help me with this question?

 

[jersey]

B=uIN/l

N=turns of wire
l= length if solenoid
u= 4(pi)(10^-7Tm/A)