Two circular coils are concentric and lie in the same plane. The inner coil contains 170 turns of wire, has a radius of 0.012 m, and carries a current of 6.2 A. The outer coil contains 220 turns and has a radius of 0.020 m. What must be the magnitude of the current in the outer coil, such that the net magnetic field at the common center of the two coils is zero

The current of the outer coil is  

Explanation:

From the question we are told that

    The number of turns of the inner coil is  

    The radius of the  inner coil is

     The current of the inner coil is  

      The number of turns of the outer coil is

      The radius of the  outer coil is

Generally the net magnetic field is mathematically represented as

Now from told that the net magnetic field is common

So  

Here   is the permeability of free space

making   the subject

substituting values

a.) travels faster in solids because the particles are closer together.

air is a gas water is a liquid

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explanation: