The heating element in an electric iron is usually made of
- A.Constantan
- B.Tungsten
- C.Nichrome
- D.Copper
Correct answer
Explanation
The correct answer is C, Nichrome. Nichrome has a high resistivity and does not oxidise easily when red hot, so it is the standard heating element.
Nichrome is an alloy of nickel and chromium (often with some iron). A heating element must turn electrical energy into heat, which needs a high resistance, and it must survive long hours at high temperature in air. Nichrome has a high melting point and forms a protective layer of chromium oxide instead of burning away, which is why it is used in electric irons, toasters, room heaters and hair dryers.
A is wrong: constantan, a copper-nickel alloy, is chosen for standard resistors and thermocouples because its resistance hardly changes with temperature.
B is wrong: tungsten is used for bulb filaments, but it oxidises quickly in air and needs an inert gas or vacuum.
D is wrong: copper has very low resistance, so it is used for connecting wires, not for producing heat.
Exam tip: heating element, Nichrome; bulb filament, Tungsten; fuse wire, tin-lead alloy; connecting wires, Copper.
Practice Questions
View allWhich one of the following frequency ranges is sensitive to human ears ?
- A.0-200 Hz
- B.20-20,000 Hz
- C.200-20,000 Hz only
- D.2,000-20,000 Hz only
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- B.between 20 Hz and 2 kHz
- C.between 2 kHz and 20 kHz
- D.greater than 20 kHz
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- B.Propane
- C.Petrol
- D.Wax
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- A.Caesium
- B.Potassium
- C.Calcium
- D.Magnesium
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- A.Na, Mg, Ca
- B.Na, Mg, Al
- C.Mg, Ca, K
- D.Mg, Ca, Ba
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