# Motional EMF Question

Hey lads, if anyone can, please check If im correct... Thanks :)

A 100 turn circular coil has a diameter of 2 cm and a resistance of 50 Ohms. The plane of the coil is perpendicular to a uniform magnetic field of magnitude 1 T. The direction of the field is suddenly reversed.

(a) Find the total charge that passes through the coil. If the reversal takes 0.1 s, find
(b) the average current in the coil and
(c) the average emf in the coil

So I got...

I= dq/dt

Е=-dф/dt

Edt/R=dQ

Integral of dQ = Q = -1/R (int from ф0 to фf) dф

= -1/R(фf-ф0) = -(delta)ф/R

ф0 (field goes inside, n vector goes inside) = NBAcos() = +NBA
фf (field goes outside, n vector goes inside) = NBAcos() = -NBA

So Q = - (-NBA-(NBA))/R = 2NBA/R = .001256C

(b) I = dQ/dt and dt= .1s
= .01256A (since dQ = Q because Q0= 0 )

(c) E=IR = 0.626V

Am I correct? If not can you please point out any mistakes I have made... thanks i very much appreciate it =)

nrqed
Homework Helper
Gold Member
Seiya said:
Hey lads, if anyone can, please check If im correct... Thanks :)

A 100 turn circular coil has a diameter of 2 cm and a resistance of 50 Ohms. The plane of the coil is perpendicular to a uniform magnetic field of magnitude 1 T. The direction of the field is suddenly reversed.

(a) Find the total charge that passes through the coil. If the reversal takes 0.1 s, find
(b) the average current in the coil and
(c) the average emf in the coil

So I got...

I= dq/dt

Е=-dф/dt

Edt/R=dQ

Integral of dQ = Q = -1/R (int from ф0 to фf) dф

= -1/R(фf-ф0) = -(delta)ф/R

ф0 (field goes inside, n vector goes inside) = NBAcos() = +NBA
фf (field goes outside, n vector goes inside) = NBAcos() = -NBA

So Q = - (-NBA-(NBA))/R = 2NBA/R = .001256C

(b) I = dQ/dt and dt= .1s
= .01256A (since dQ = Q because Q0= 0 )

(c) E=IR = 0.626V

Am I correct? If not can you please point out any mistakes I have made... thanks i very much appreciate it =)

This looks completely right to me.