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.

The pzzls eye test

Close one of your two eyes. Move your head close to the monitor and watch concentratedly to the left circle if you closed your left eye. You should look to the right circle if you closed your right eye. Keep watching and move your head slowly backwards while checking the other circle. What happens? And how is that possible?