Tilley’s Circuit

This electrical circuit near the permanent magnet has two ideal switches and a galvanometer. When switch A is closed and switch B, on the right, is opened, there is a large change in the magnetic flux in the galvanometer circuit. What do you predict the galvanometer response will be?

Answer

The galvanometer does nothing! There is no induced potential because no work was done (assuming frictionless switches). This result appears to violate Faraday’s law V = dΦ/dt, where V is the potential difference induced by the rate of change of magnetic flux Φ. But work must be done for V to be generated because the change in the work dWork = V dt.