--- title: "Methods of electric heating" subject: "Utilization of Electrical Energy" chapter: 5 key: "semester_7/utilization_of_electrical_energy:methods-electric-heating" source: https://www.bctengineer.com/q/semester_7/utilization_of_electrical_energy/methods-electric-heating site: BCT Engineering --- # Methods of electric heating Utilization of Electrical Energy · Chapter 5: Electric Heating - Asked in: 2069 Chaitra - Video: [Electric heating | Utilization of electrical energy |UEE 6th semester | Heating methods |polytechnic](https://www.youtube.com/watch?v=Na8gJWExeq8) — Careers for Engineers - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/utilization_of_electrical_energy/methods-electric-heating - Whole chapter: https://www.bctengineer.com/md/semester_7/utilization_of_electrical_energy/chapter-5 ## Question Explain in brief the various methods of electric heating used in industrial and domestic purpose. ## Short answer Electric heating methods are classified as power-frequency (resistance, arc, core-type induction) and high-frequency (coreless induction, dielectric, microwave). Resistance heating uses I²R loss directly or indirectly; arc heating uses an electric arc; induction heating induces eddy currents; dielectric heating heats insulators; infrared and microwave are also employed. ## Answer **Electric heating** converts electrical energy into heat. The main methods are classified as power-frequency and high-frequency heating. ```text Electric heating +-------------+-------------+ Power frequency High frequency |-- Resistance |-- Induction (coreless) | direct / indirect |-- Dielectric | (incl. infrared) |-- Microwave |-- Arc | direct / indirect |-- Induction (core type) ``` #### 1. Resistance heating Heat is produced by $I^2R$ loss. - **Direct:** current passes through the charge itself (e.g. salt-bath furnace, electrode boiler, resistance welding). - **Indirect:** current passes through a heating element (nichrome, Kanthal) and heat reaches the charge by radiation and convection. Examples: **room heaters, electric irons, kettles, water heaters, cooking ranges, ovens** (domestic) and resistance ovens for annealing and drying (industrial). #### 2. Arc heating An electric arc between electrodes produces about 3000–3500°C. - **Direct arc:** arc between electrodes and charge; current flows through the charge (steel-making arc furnace). - **Indirect arc:** arc between two electrodes above the charge; heat reaches it by radiation (melting of brass, copper). - Also used in arc welding. #### 3. Induction heating Eddy currents (and hysteresis loss) are induced in a conducting charge by an alternating field. - **Core type (low frequency):** Ajax-Wyatt furnace for melting brass and non-ferrous metals. - **Coreless (high frequency):** steel and alloy melting, surface hardening, brazing; **induction cooktops** in homes. #### 4. Dielectric heating Non-conducting materials between electrodes at 10–50 MHz are heated by dielectric loss, uniformly through the volume. Used for gluing plywood, welding plastics, drying textiles and food processing. #### 5. Infrared heating A form of indirect resistance heating: tungsten-filament (infrared) lamps radiate heat onto a surface. Used for drying paints and varnishes, and in some domestic heaters. #### 6. Microwave heating A magnetron (2.45 GHz) heats water-containing material from inside. Used in **microwave ovens** at home and for industrial food drying. | Method | Domestic use | Industrial use | |---|---|---| | Resistance | Iron, kettle, heater, oven | Annealing, drying ovens | | Arc | — | Steel melting, welding | | Induction | Induction cooktop | Melting, hardening | | Dielectric | — | Plywood, plastics | | Microwave | Microwave oven | Food processing | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In direct resistance heating, how is the charge heated? A. Current passes through the charge itself, producing I^2R loss B. Current flows in a separate element and heat reaches the charge by radiation only C. Eddy currents are induced in the charge by an alternating field D. An arc is struck between two electrodes above the charge Answer: A. In direct resistance heating the charge is part of the circuit and heats by I^2R; in indirect heating a separate element is used. (Key point: Resistance heating principle) 2. In an indirect arc furnace (e.g. melting brass or copper), how does heat reach the charge? A. Current from the arc flows through the charge B. By radiation from an arc struck between two electrodes above the charge C. By eddy currents induced in the charge D. By dielectric loss in the charge Answer: B. In indirect arc heating the arc is between electrodes and the charge is heated by radiation; in direct arc heating current flows through the charge. (Key point: Arc heating types) 3. Which feature describes dielectric heating? A. Conducting material is heated at the surface by eddy currents B. A magnetron at 2.45 GHz heats the surface only C. Non-conducting material between electrodes at 10-50 MHz is heated uniformly through its volume by dielectric loss D. Infrared lamps heat the material by conduction Answer: C. Dielectric heating works on insulators in a high-frequency field and heats the whole volume, e.g. for gluing plywood. (Key point: Dielectric heating) 4. Which is the correct pairing for induction furnaces? A. Core type is high frequency; coreless is low frequency B. Both types use dc supply C. Core type is used for induction cooktops; coreless for brass only D. Core type is low frequency (Ajax-Wyatt); coreless is high frequency (steel melting, surface hardening) Answer: D. The core-type furnace runs at low frequency for non-ferrous metals; coreless furnaces use high frequency for steel, hardening and cooktops. 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