Question

6. Mike Faraday folds 4 meters of copper wire (cross-section 10-7 m2) into a square and holds it in a uniform magnetic field of strength 2.0 Tesla. The field passes directly through the “circuit”—pointing towards Mike’s face as he looks down at his square. a) Over what time interval should Mike’s assistant crank up the field to 5.0 Tesla if Mike hopes to achieve a current of 0.5 A? b) Will Mike observe a clockwise current or a counterclockwise current?

Answer 1

PART A:

The length of one side of the square is

So, the area of the square loop is

The resistivity of copper is 1.68 x10^-8 Ohm.meter.

The cross-section area of the wire is

So, the resistance of the wire is

The induced emf is given by the rate of change of the magnetic flux through the loop. i.e

And the current through the circuit can be calculated using

Now putting the values in the equation in SI units.

So, the interval of change of the magnetic field is 8.93 s.

PART B:

Lenz's law states that the induced current will tend to oppose the cause of the induction.

Now, we know the magnetic field is increasing out of the page. So, to oppose this the induced current must be generated in such a manner the magnetic field produced by it must be directed inside the page. And by right-hand thumb rule, we come to conclude that the direction of induced current must be clockwise.