Thunder and lightning

Why does a flash of lightning take only an instant, while the corresponding thunder can last for a few seconds? You might have expected that that the sound is caused by the flash, and that the thunder should therefore be audible also for an instant.

Voltage voodoo

In the figure, an electrical circuit is drawn. In the middle of the circuit a infinitely long metal bar is placed indicated with the grey circle. In this bar, an oscillating magnetic field is induced by a coil which is attached somewhere to the bar. Two resistors are located in the circuit with values R1 and R2. The alternating voltages V1 and V2 are being measured with two perfect alternating voltages meters. What is the relation between the two voltages V1 and V2? a) V1 : V2 = R2 : R1 b) V1 : V2 = 1 : 1 c) V1 : V2 = R1 : R2 d) V1 = V2 = 0 e) something different.

Einstein as a speed devil

How fast should you drive towards a red traffic light to see it appear as green?