Question

In a physics laboratory experiment, a coil with 180 turns. Each turn of the coil encloses an area of 12 cm2 . The coil is rotated from a position where its plane is perpendicular to the earth's magnetic field to one where its plane is parallel to the field. The rotation takes 3.4×10⁻² s . The earth's magnetic field at the location of the laboratory is 6.0×10⁻⁵ T.

A) What is the magnetic flux through one turn of the coil before it is rotated? The SI unit for magnetic flux is the Weber (Wb), which is equal to Tm^2.

B) What is the magnetic flux through one turn of the coil after it is rotated?

C) What is the average emf induced in the coil as it is rotated from the perpendicular to the parallel orientation?

Answer 1

a)

φ = BA cos θ

θ = 0 = maximum

φ = 6 x 10^-5 T x 12 x 10^-4 m^2 x cos(0)

φ = 7.2 x 10^-8 T-m^2 or wb

b)

After rotating the loop, flux is zero because the loop isparallel to the field. cos 90 = 0. For the angle you look at

the angle between the perpendicular drawn to the face of the loop and the field.

φ = 0

c)

ε = - NΔφ/Δt

When you go from initial to final,the flux changes from a higher value to 0. Therefore, the flux willbe negative and the

negative sign in the equation will take care ofthe negative flux.

ε = (-180 x - 7.2 x 10^-8) / (3.4 x 10^-2)

ε = 3.81 x 10^-4 wb/s