Applications of heating effect of electric current - class-VIII

According to heating effect of electric current, heat is produced in the materials that have resistance, thus electric immersion water heater, electric iron box and electric fuse are the applications of heating effect of electric current.

Bulbs are filled with chemically inactive Nitrogen or Argon gas to prevent the oxidation of tungsten filament used in the bulb.

An electric fuse in households works on the principle of Joule's heating that heat produced due to the excess current flowing through it melts the fuse wire which cut off the circuit and hence the appliance is prevented from damage.

For constant electric power, higher the voltage, lower is the current (as $P=IV$) through the wire. As power loss due to Joule's heating is proportional to $I^2$, for a small current, power loss is also small. So, power is transmitted over long distances at high voltage to minimize power loses due to Joule's heating.

Joule's Law of heating states that the heat produced in a conductor is H = I^2 * R * t, where I is current, R is resistance, and t is time.

Because, alloy of nickel and chromium has high resistivity,

The resistance of filament should be high so that it can produce heat and light and its melting point should also be high so that it does not melt at the high temperature at which it is producing light.

The resistance of the filament varies with temperature. At operating temperature (2000°C), R_hot = V²/P = 220²/100 = 484Ω. Using the temperature coefficient formula: R_cold = R_hot/(1 + α(2000-0)) = 484/(1 + 0.005×2000) = 484/11 = 44Ω. Initial current = V/R_cold = 220/44 = 5A. However, this is an approximation - the actual surge current depends on how quickly the filament heats up. Given the options, 4.5A is the closest reasonable estimate.

Answer is A.

Most heating elements use Nichrome 80/20 (80% nickel, 20% chromium) wire, ribbon, or strip. Nichrome 80/20 is an ideal material, because it has relatively high resistance and forms an adherent layer of chromium oxide when it is heated for the first time. Material beneath this layer will not oxidize, preventing the wire from breaking or burning out.
Hence, nichrome is used as heating elements.

An electric iron is based on the principle of heating effect of current that heat is produced in the nichrome wire used in the iron due to the current flowing through it.

The overheating of electrical wiring in any circuit due to the flow of large current through it is called overloading of electric current.

Electrical working is based on Joule's law, i.e. heating effect of electric current in a conductor.

Electric Fan works on the principle of motor.

Nichrome is used for making heating element of electrical appliances. Because nichrome does not oxidize and burn easily at high temperature i.e.it has higher melting and boiling point than metals. Thus it does not melt even when a large amount of heat is produced due to passage of current. Moreover, It has higher resisistivity and consequently a higher resistance.Therefore, it will resist the flow of charges more, and lead to development of heat faster.

Tungsten is used in electric bulb because it has high melting point and it does not oxidize. Thus tungsten filament does not melt even when a large amount of heat is produced due to passage of current through the filament (via heating effect of current).

A device which works on Joule's law of heating ;