This set of 20 multiple choice questions (MCQs) covers key concepts like resistance heating, induction heating, dielectric heating, heating elements, and efficiency — with detailed explanations to boost your understanding. Ideal for quick revision and concept clarity!
1. Which of the following is an advantage of electric heating?
A) Quicker operation
B) Higher efficiency
C) Absence of flue gases
D) All of the above
Answer: D
Explanation: Electric heating offers faster operation, higher efficiency, and cleaner operation without flue gases.
2. In a domestic electric iron, temperature is controlled by:
A) Controlling current
B) Controlling voltage
C) Using thermostat
D) Adding resistance in series with heating element
Answer: C
Explanation: Thermostats regulate the temperature by switching the heating element on and off to maintain the desired heat level.
3. Which of the following heating elements has the lowest operating temperature?
A) Graphite
B) Kanthal
C) Eureka
D) Nichrome
Answer: C
Explanation: Eureka, an alloy of nickel and copper, operates at lower temperatures compared to other heating elements.
4. Which method of electric heating involves passing electrical energy through a heating element to generate heat?
A) Resistance heating
B) Induction heating
C) Dielectric heating
D) Infrared heating
Answer: A
Explanation: In resistance heating, electrical energy is converted into heat energy by passing current through a resistive material.
5. Dielectric loss in dielectric heating is proportional to:
A) Frequency
B) Square of frequency
C) Square root of frequency
D) Cube of frequency
Answer: B
Explanation: Dielectric loss increases with the square of the applied frequency.
6. Which of the following advantages of electric heating is represented by no irritating noise and low radiation losses?
A) Cleanliness
B) Ease of control
C) Better working conditions
D) High efficiency
Answer: C
Explanation: Electric heating provides a quieter and more comfortable environment with minimal radiation losses.
7. In resistance heating, the highest working temperature is obtained from heating elements made of:
A) Nickel-copper
B) Nichrome
C) Silicon carbide
D) Silver
Answer: C
Explanation: Silicon carbide heating elements can withstand higher temperatures.
8. Which of the following methods of heating is independent of supply frequency?
A) Induction heating
B) Dielectric heating
C) Electric resistance heating
D) All of the above
Answer: C
Explanation: Electric resistance heating relies on the material's resistance and is not affected by supply frequency.
9. A good heating element should have:
A) High resistivity and low melting point
B) Low resistivity and high melting point
C) High resistivity and high melting point
D) Low resistivity and low melting point
Answer: C
Explanation: High resistivity ensures effective heat generation, and a high melting point allows operation at elevated temperatures.
10. In salt bath heating, the current is allowed to flow only through the:
A) Electrodes
B) Workpiece
C) Molten salt
D) Heating element
Answer: C
Explanation: Electrical current passes through molten salt, generating heat that uniformly heats the workpiece.
11. Which heating method uses high-frequency electromagnetic waves to heat non-conductive materials?
A) Resistance heating
B) Induction heating
C) Dielectric heating
D) Infrared heating
Answer: C
Explanation: Dielectric heating uses high-frequency electromagnetic fields to heat insulating materials by molecular vibration.
12. In induction heating, heat is produced in the material due to:
A) Resistance of the material
B) Hysteresis and eddy current losses
C) Dielectric losses
D) Conduction losses
Answer: B
Explanation: Induction heating generates heat through hysteresis and eddy current losses in the material subjected to an alternating magnetic field.
13. Which of the following is not a characteristic of a good heating element?
A) High resistivity
B) Low temperature coefficient of resistance
C) Low melting point
D) High oxidation resistance
Answer: C
Explanation: A good heating element should have a high melting point to withstand high operating temperatures.
14. The efficiency of electric heating is generally:
A) 30-40%
B) 50-60%
C) 75-80%
D) 90-100%
Answer: D
Explanation: Electric heating systems can achieve efficiencies close to 100% as nearly all the electrical energy is converted into heat.
15. Which material is commonly used for the filament in incandescent lamps?
A) Copper
B) Aluminum
C) Tungsten
D) Nickel
Answer: C
Explanation: Tungsten has a high melting point and low vapor pressure, making it suitable for use as a filament in incandescent lamps.
16. Which of the following materials is used as a heating element in electric kettles and toasters?
A) Copper
B) Nichrome
C) Silver
D) Aluminum
Answer: B
Explanation: Nichrome is widely used due to its high resistivity, high melting point, and good oxidation resistance.
17. In induction heating, the depth of penetration of heat is:
A) Inversely proportional to frequency
B) Directly proportional to frequency
C) Independent of frequency
D) Constant for all materials
Answer: A
Explanation: As frequency increases, the depth of heat penetration decreases, which is ideal for surface hardening.
18. Which method of electric heating is best suited for surface hardening of steel?
A) Dielectric heating
B) Infrared heating
C) Resistance heating
D) Induction heating
Answer: D
Explanation: Induction heating is ideal for surface hardening as it heats only the surface quickly and efficiently.
19. The process of heating the entire volume of non-metallic materials like plastics using high-frequency electric fields is known as:
A) Infrared heating
B) Arc heating
C) Dielectric heating
D) Resistance heating
Answer: C
Explanation: Dielectric heating heats the entire volume of insulating materials by molecular friction caused by high-frequency electric fields.
20. Which of the following is not a type of resistance heating?
A) Direct resistance heating
B) Indirect resistance heating
C) Arc heating
D) Infrared heating
Answer: C
Explanation: Arc heating involves electric arcs and is a separate method, not a type of resistance heating.