Skin effect: Metal sheet shielding varies with frequency.

• D+15+22

Skin effect: Metal sheet shielding varies with frequency. This apparatus demonstrates the 'Skin effect'. The signal generator supplies a sinusoidal voltage to the first coil of wire, creating an sinusoidal magnetic field. The magnetic field penetrates the aluminum sheet. In the aluminum, if the flux phi= ASin omega*t, then the induced voltage = dphi/dt =A*omegaCos omega*t. Thus, as omega gets larger, the induced voltage in the aluminum gets larger; the resultant eddy currents get larger; the repelling B-field from the eddy currents gets larger which helps to cancel out the B-field from the first coil. The net effect is that the B-field in the aluminum dies away exponentially as it leaves the front surface. This 'Skin effect' is minimal at low frequencies (10 Hz), and most of the B-field gets through the back surface to be picked up by the second coil. At high frequencies (10KHz and higher) little of the B-field gets through and the aluminum acts as a shield. Note: See set-up sheet in file cabinet in 72 Le Conte Hall FARADAY'S LAW.