3 a Explain why many times lightning bolts appear to flicker

3.

a. Explain why many times lightning bolts appear to flicker.

b. You see a flash of lightning, and then hear a boom of thunder 3 seconds later. How far away is the lightning in meters (or kilometers)? Should you implement lightning safety procedures?

c. Identify and describe what red sprites and blue jets are.

4. Lightning

Solution

3a)

According to Uman, the German scientist Pockels discovered that basalt rock in the vicinity of lightning strikes was magnetized and deduced currents on the order of 10,000 amps in 1897. Ampere\'s law allows you to deduce the current in a wire from the measurement of the magnetic field at some radius from the wire. Pockels presumably had measured the magnetizing effects of large currents on basalt and was able to scale those experiments to estimate the current associated with the lightning. Based on that principle, magnetic links are widely used for the measurement of the lightning currents. Most measurements have been in the range 5,000 to 20,000 amps but a famous strike just before the Apollo 15 launch in 1971 was measured at 100,000 amperes by magnetic links attached to the umbilical tower. Currents over 200,000 amps have been reported.

One could envision a magnetic detector based on both Ampere\'s law andFaraday\'s law which could give you an estimate of lightning current provided you had a measurement of the distance from the detector to the lightning strike point. If you set up a coil of wire in a vertical plane, then the rate of change of magnetic field through the coil would generate a voltage. If you could sum (integrate) the current generated by that voltage, you could calculate the charge transferred in the lightning strike. With several such detectors in an area, you could model the location as well as the charge associated with the strike.

Most commonly, the lightning current ceases in about a millisecond for a given stroke, but sometimes there is a continuing current on the order of 100 amps following one or more of the strokes. This is called \"hot lightning\" and it is the cause of lightning fires according to Uman. The temperatures of lightning are 15,000-60,000