This apparatus shows the effect of temperature on resistance of a common metal, such as copper. The idea is simple. A 0.5 mm diameter, 100 feet copper wire of resistance 13Ω is connected in series with 12V bulb and a DC power supply. The voltage is adjusted to 7V so the bulb glows dimly. When the coil is immersed in liquid nitrogen, the resistance drops, causing the bulb to glow brightly because the current has now gone up. This is a nice, simple demonstration liked by students, especially with the fun of watching of liquid nitrogen.