Back burning, starting fires infront of the main fire to prevent the fire from spreading and depleting fuel for the fire, digging trenches so the fire has no where to go, dropping water from planes or helicopters.
1.) A semiconductor is a device whose conductivity lies between the conductivity of the conductors and the insulators.
2.) A Zener diode is a semiconductor device made of silicon that allows current to flow in both directions.
<h3>What is a semiconductor?</h3>
A semiconductor is a device whose conductivity lies between the conductivity of the conductors and the insulators.
Due to the inclusion of an impurity or temperature effects, a solid substance with conductivity between that of an insulator and that of most metals. Semiconductor devices, particularly silicon devices, are key components of most electronic circuits.
Zener diode:-
A Zener diode is a semiconductor device made of silicon that allows current to flow in both directions.
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Explanation:
The two types of furnaces used in steel production are:
<u>Basic oxygen furnace </u>
In basic oxygen furnace, iron is combined with the varying amounts of the steel scrap and also small amounts of the flux in the Blast Furnace. Lance is introduced in vessel and blows about 99% of the pure oxygen causing rise in temperature to about 1700°C. This temperature melts scrap and the impurities are oxidized and results in the liquid steel.
<u>Electric arc furnace</u>
Electric arc furnace reuses existing steel. Furnace is charged with the steel scrap. It operates on basis of electrical charge between the two electrodes providing heat for process. Power is supplied through electrodes placed in furnace, which produce arc of the electricity through scrap steel which raises temperature to about 1600˚C. This temperature melts scrap and the impurities can be removed through use of the fluxes and results in the liquid steel.
Answer:
D. a measure of how fast a machine performs work
Explanation:
Power can be defined as the energy required to do work per unit time.
Mathematically, it is given by the formula;
Hence, the best description of power is that, it is a measure of how fast a machine performs work.
This can be calculated by using the mathematical expression below;
But we know that, 
