Heating Effect of Electric Current: Essential for Safe Energy Use

The heating effect of electric current is a phenomenon in which the passage of electric current through a conductor produces heat. Understanding the heating effect of electric current is crucial for designing efficient electrical devices and ensuring safe and controlled energy transformations in electronic systems.

Understanding the Heating Effect of Electric Current: Basics and Joule’s Law

• Concept: Flow of electric current in an electric device/wire produces heat. 
  • This is the heating effect of electric current. 
• Appliances: Electric heater used for cooking, electric iron, an electric bulb or room heater are some appliances which show the heating effect of electric current flows.
• Power Input: If a current is flowing through a resistor of resistance R and potential difference across it be V, t is the time during which a charge Q flows across and the work done in moving the charge Q through a potential difference V is VQ. 
  • Then the power input to the circuit by the source is –P =VQt  = VI  
  • Or the energy supplied to the circuit by the source in time t is P × t, that is, V x I x t. 

• This energy is dissipated in the resistor as heat. 
• Thus for a steady current I, the amount of heat H produced in time t is H = VIt.
• By Applying Ohm’s law, we get H = I2Rt. This is known as Joule’s law of heating.
• Joule’s law of heating: The law implies that heat produced in a resistor is

1. 1. directly proportional to the square of current for a given resistance,
   2. directly proportional to resistance for a given current, and
   3. directly proportional to the time for which the current flows through the resistor.

Elements and Their Heating: Material, Length, and Efficiency

• All electrical heating devices consist of a coil of wire called an element. 
• Part of Appliances: Electrical appliances, such as immersion heaters, hotplates, irons, geysers, electric kettles, hair dryers, have elements inside them. 
• Radiating Heat: When these appliances are connected to the electric supply, their elements become red hot and give out heat.
• Dependent Factors: The amount of heat produced in a wire depends on its material, length and thickness. 
  • Thus, for different requirements, the wires of different materials, lengths and thicknesses are used.

Practical Applications of Heating Effect of Electric Current: Appliances, Lighting, and Safety

• Heat Generation in Conductors: The generation of heat in a conductor is an inevitable consequence of electric current but in many cases, it is undesirable as it converts useful electrical energy into heat. 
• Altering Properties: In electric circuits, the unavoidable heating can increase the temperature of the components and alter their properties. 
• Useful Applications: The electric laundry iron, electric toaster, electric oven, electric kettle and electric heater are some of the familiar devices based on Joule’s heating.
• Produce Light: The electric heating is also used to produce light, as in an electric bulb. 
• Retention of Heat: Here, the filament must retain as much of the heat generated as is possible, so that it gets very hot without melting and emits light. 

• Bulb Filament: A strong metal with a high melting point such as tungsten (melting point 3380°C) is used for making bulb filaments.
• Thermal Isolation: The filament should be thermally isolated as much as possible, using insulating support, etc.
• Inert Gasses: The bulbs are usually filled with chemically inactive nitrogen and argon gases to prolong the life of filament.
• Radiated as Light: Most of the power consumed by the filament appears as heat, but a small part of it is in the form of light radiated.

• Making of Fuse: Another application of Joule’s heating is the fuse used in electric circuits. 

Fuse: Essential Safety Device for Preventing Electrical Fires

• Safety Device Overview: It  is a safety device that protects circuits and appliances by stopping the flow of any unduly high electric current and prevents electric fires. 
• Placement in Circuit: The fuse is placed in series with the device. 
  • It consists of a piece of wire made of a metal or an alloy of appropriate melting point.
  • Example:  Aluminium, copper, iron, lead etc. 
• Wires for Fuse: Wires used for making electric fuses are made from some special materials which melt quickly and break when large electric currents are passed through them.
  • The fuse wire is usually encased in a cartridge of porcelain or similar material with metal ends.

• Rating: The fuses used for domestic purposes are rated as 1 A, 2 A, 3 A, 5 A, 10 A, etc.
  • In all buildings fuses are inserted in all electrical circuits. 
  • Also, there is a maximum limit on the current which can safely flow through a circuit. 
    • If by accident the current exceeds this safe limit, the wires may become overheated and may cause fire. 
    • If a proper fuse is there in the circuit, it will blow off and break the circuit.
  • Fuses of different kinds are used for different purposes.
  • One must always use proper fuses which have been specified for particular applications, carrying an ISI mark.
  • One disadvantage of a fuse is that once the filament of the fuse is broken, it needs to be replaced. 
    • This is a time consuming process. 
    • This challenge can be overcome by Miniature Circuit Breaker (MCB).