A magnetometer is an instrument which measures magnetic field strength. Sometime

Question

A magnetometer is an instrument which measures magnetic field strength. Sometimes magnetometers are made using coils which generate an EMF in response to the magnetic fields according to Faraday's Law. Consider a magnetometer which is made as follows A large circular coil has an area of 0.2 m2. It contains N turns of wire. initial final In the initial orientation, the magnetic field is parallel to the plane of the coil. Then the coil is quickly rotated through 90 to the final orientation. The magnetic flux through the coil changes as the coil is flipped, with the change given by initial. (a) Write an expression which gives Apu in terms of B. (b) Suppose the coil is flipped during a time interval ? t-0.1 s. Use Faraday's Law to show that the EMF which is generated as the coil is flipped is equal to 2NB. (Ignore the minus sign in Faraday's Law.) (c) Finally, suppose that we want to use the coil to generate an EMF equal to 10 mV when we flip it in a magnetic field equal to 10 T. (This is approximately the earth's field.) Find the number of turns of wire in the coil.

Explanation / Answer

a.Flux is given by Phi= B A cos theta where B is magnetic field,A is cross sectional area, theta is the angle between B and the direction of Area(Perpendicular to the area)

b. Emf= - change in flux/time =- (0.2*NB cos 0-0.2NB cos 90)/0.1= 2 NB

c. 10*10-3=2*N*10-4

N=50

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