define heating effect chapter electricity class 10th NCERT
Answers
Heating effect of electricity is one of the widely used effects in the world. When electric current is passed through a conductor, it generates heat due to the resistance it offers to the current flow. The work done in overcoming the resistance is generated as heat.
This is studied by James Prescott Joule and he enunciated various factors that affect the heat generated. The heat produced by a heating element is directly proportional to the square of the electric current (I) passing through the conductor, directly proportional to the resistance (R) of the conductor, time (t) for which current passes through the conductor. It is given by the expression
H = I2Rt and is well known as Joule’s Law.
Applications of the heating effect of electric current include appliances like electric immersion water heater, electric iron box, etc. All of these have a heating element in it. Heating elements are generally made of specific alloys like, nichrome, manganin, constantan etc.
A good heating element has high resistivity and high melting point. An electric fuse is an example for the application of heating effect of electric current. The rating of 3 A of an electric fuse implies the maximum current it can sustain is three ampere.
The chemical reaction within the cell generates the potential difference between its two terminals that sets the electrons in motion to flow the current through a resistor or a system of resistors connected to the battery. To maintain the current, the source has to keep expending its energy.
A part of the source energy in maintaining the current may be consumed into useful work (like in rotating the blades of an electric fan). Rest of the source energy may be expended in heat to raise the temperature of gadget. For example, an electric fan becomes warm if used continuously for longer time, etc.
If the electric circuit is purely resistive, that is, a configuration of resistors only connected to a battery, the source energy continually gets dissipated entirely in the form of heat. This is known as the heating effect of electric current. When a conductor offers resistance to the flow of current the work done by the electric current in overcoming this resistance is converted into heat energy.
The generation of heat in a conductor is an inevitable consequence of electric current. In many cases, it is undesirable as it converts useful electrical energy into heat. In electric circuits, the unavoidable heating can increase the temperature of the components and alter their properties.
The electric heating is also used to produce light, as in an electric bulb. Here, the filament must retain as much of the heat generated as is possible, so that it gets very hot and emits light. It must not melt at such high temperature. A strong metal with high melting point such as tungsten (melting point 3380°C) is used for making the filaments of the bulb. The filament should be thermally isolated as much as possible, using insulating support, etc. The bulbs are usually filled with chemically inactive nitrogen and argon gases to prolong the life of filament. Most of the power consumed by the filament appears as heat, but a small part of it is in the form of light radiated.
Devices which work on the heating effect of electric current have a heating element or filament. Good heating elements have high resistivity, high melting point and negligible variation in resistance due to temperature changes.
The three metal alloys most commonly used as heating elements are: Nichrome (80% Ni + 20% Cr); Manganin (86% Cu + 12% Mn + 2% Ni); Constantan (60% Cu + 40% Ni).
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