Question

The magnetic field produced by a toroid

1) falls off as 1/r away from the toroid.

2) is nearly zero outside the toroid.

3) is a uniform field

4) is four times that produced by a hemiroid.

Answer 1

Answer : (2) is nearly zero outside the toroid.

The magnetic field inside and outside the toroid is zero.

According to Ampere's law which states that integration of magnetic field over an amperian loop is equivalent to constant μ multiplied by current enclosed. Now, the current that flows at outer circumference and inner circumference of toroid are in opposite direction to each other. Therefore, current enclosed by Amperian loop is zero. Thus, magnetic field outside the toroid is zero.