# Quiz 20: Induced Voltages and Inductance

Faraday's law of induction states that the instantaneous electromotive force (emf) induced in the circuit is equal to the negative rate of the change in the magnetic flux through the coil. Here, is the number of coils, is the rate of change of the magnetic flux. Use the Faradays law of induction, then the change in the magnetic flux in the coil will produce an emf. When the spacecraft orbiting earth, then it will moves from one region of magnetic field strength to another region of magnetic field strength. Hence, the changing the magnetic field through the coil in the spacecraft induces as emf. Due to this reason, there is a current in the coil.

The expression for the magnetic flux through the loop which is placed in the magnetic field is, Here, B is the strength of the magnetic field, A is the area of cross-section of the loop, and is the angle between the magnetic field and the normal to the plane of the loop. The expression for the area of the rectangular loop is, Here, l is the length of the loop, and b is the breadth of the loop. Substitute 12 cm for l , and 8.0 cm for b in . Thus, the area of the rectangular loop is Substitute 0.50 T for B , for A , and in . Therefore, the flux through the loop whose plane is perpendicular to the magnetic field is .

Lenz's law says that the induced magnetic field should be directed in such a way that it opposes the original cause that produces it. If the bar magnet approaches the coil, there will be change in the magnetic flux through the coil. Thus, the induced current in the coil will be directed in such a way that the magnetic field produced due to the induced current opposes the cause that produces it. Assume the copper tube as a set of coils which are stacked together. If the bar magnet approaches the tube, there will be change in magnetic flux through the tube due to which the current is induced in it. This current will be directed along the circumference of the tube.