
Answer:
B_2 / B_1 = 0.5 , Half of magnetic field at distance d.
Explanation:
Given:
- A current carrying conductor produces a magnetic field = B_1 Â @ r = d
- A current carrying conductor produces a magnetic field = B_2 Â @ r = 2*d
Find:
Compare the the magnetic Field at two points r = d and r = 2*d:
Solution:
- The magnetic Field of long current carrying wires are expressed as follows:
                   B = u_o*I / 2*pi*r
Where,
B = Magnetic Field
I = The current in the conductor
r = The radial distance from the center of the wire.
u_o = Permittivity of free space (constant)
- Now compute B_1 and B_2:
                  B_1 =  B = u_o*I / 2*pi*d
                  B_2 =  B = u_o*I / 4*pi*d
- Take a ratio of B_2 to B_1:
                  B_2 / B_1 = (u_o*I / 4pi*d) * ( 2*pi*d/u_o*I)
                  B_2 / B_1 = 0.5
- Hence, the magnetic field at distance 2d is half of the magnetic field at distance d.