The current induced in the coil creates another field, in the opposite direction of the bar magnet’s to oppose the increase. Lenz’ Law: (a) When this bar magnet is thrust into the coil, the strength of the magnetic field increases in the coil. Faraday was aware of the direction, but Lenz stated it, so he is credited for its discovery. The direction (given by the minus sign) of the EMF is so important that it is called Lenz’ law after the Russian Heinrich Lenz (1804–1865), who, like Faraday and Henry, independently investigated aspects of induction. Now let’s explain the flux through each one of those open areas. In fact, these rectangles represent one rectangle with different orientations. To use Gauss’s law effectively, you must have a clear understanding of what each term in the equation represents. To get a better understanding of what electric flux is, I’ll bring into this electric field three rectangles. The flux of the electric field E through any closed surface S (a Gaussian surface) is equal to the net charge enclosed (qenc) divided by the permittivity of free space (0): SE ndA qenc 0. The minus means that the EMF creates a current I and magnetic field B that oppose the change in flux Δthis is known as Lenz’ law. The unit of electric flux is Newton meters squared per Coulomb (Nm2/C). Example 2: A solenoid of diameter 40 cm has a magnetic field of 2.9 × 105 N/Amps m. This is equal to Q enclosed divided by E 0, or A divided by E 0. The magnetic field generated by the solenoid is 8.505 × 10 4 N/Amps m. The minus sign in Faraday’s law of induction is very important. The magnetic field in a solenoid formula is given by, B oIN / L. The units for EMF are volts, as is usual. The Coulombs law equation was usually correctly recalled at the start of candidates answers to part (b) (i), and was often followed by an acceptable value for. This relationship is known as Faraday’s law of induction.
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