State the effect of rise in temperature of the filament
Answers
It depends on what material the filament is made. Generally speaking, metals increase in resistance as they increase in temperature. Non conductors and semiconductors generally decrease in resistance as temperature increases. One of the reasons that metals are most often used for filaments is that very property, which makes them safer and last longer. As the filament gets hotter, its resistance increases, thus reducing the current and consequent wattage. The old carbon filament lamps would decrease in resistance as they got hotter, increasing their power consumption, and consequent wattage and temperature. Insulators are always non metallic, which makes it necessary that their insulating quality (resistance) is greater than needed by design, because as they heat up, their resistance drops.