An engineer is designing a device that requires a precise and constant temperature to incubate bacterial cultures. Which principle should primarily guide the choice of the heating element for this device, considering the applications of the heating effect of current?
Using a material with suitable resistance to produce sufficient heat
By Joule's law of heating, the heat produced in a conductor is \(H = I^{2}Rt\). For a fixed supply, the heat produced depends on the resistance of the heating element, so the element must be chosen with the right resistance.
An incubator needs a steady, controlled amount of heat, enough to hold the cultures at the required temperature but not more. A material with suitable resistance (for example nichrome, which also does not oxidise easily when hot) produces sufficient heat steadily, and the temperature can then be held constant with a thermostat.
Increasing the current continuously would make the heat keep rising, so the temperature would not stay constant and could damage the cultures. A low-resistance material, or one that prevents heat production, would not provide the heat the device needs.
Hence, Using a material with suitable resistance to produce sufficient heat.
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