A circular loop is conducting current in a counter-clockwise direction as shown.

Question

A circular loop is conducting current in a counter-clockwise direction as shown. A number

of changes to this initial situation are described in a-e below. In each case, describe how the

proposed changes will affect the magnitude and direction of the magnetic field at the center

of the loop and explain your reasoning.

Each change below refers to the initial situation described above.

a. The current in the loop is increased.

b. The direction of the current in the loop is reversed.

c. The current in the loop is reduced and its direction reversed.

d. The radius of the loop is increased.

e. The radius of the loop is decreased and the current is increased.

f. The loop is replaced by a coil with several turns with the same radius and current.

Explanation / Answer

magnetic field at the centre is given by B = n*mu*I/2*pi*R, n is number of turns, I is current and R is radius

a)as the current is increased we can see that the magnetic field will increase because it its directly proportional to I the direction will remain the smae

b)when the direction of I is reversed the magnitude remains same but the direction of B also reverse.If we apply the right hand rule that is when we curl our fingers int he direction f current the direction of B is given by the direction the thumb is pointing to

c)the magnitude will be halved and the direction will reverse by applying the logics of a nad b

d) if the radius is increased the magnitude of the B will decrease as it is incersely proportional to R the direction is independent f R so it remains the smae

e)the direction remaisn same for B but for the magnitude will increase because B is directly proportional to I and inversely proportional to R

f) the magnitude of B will increase by n time where n is the number of turns as B is directly proportional to n

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