Electric Heating MCQs

21. Which of the following does not uses heating effect of electric current?

1. Electric furnace
2. Geyser
3. Electric iron 
4. Vacuum cleaner

22. A nichrome wire used as a heater coil has the resistance of 1 ohm meter for a heater of 1000 W at 200V. The length of wire required will be

1. 5 m
2. 20 m
3. 40 m
4. 50 m

23. In which type of water heater the heat rays from an element brought up to red heat by the passage of electric current travel through the air rapidly and raise the temperature of the solid substance in the surroundings which falls is its range. 

1. Three heat switch
2. Electric iron
3. Electric oven heating
4. Electric radiator

24. Power-factor of industrial arc and induction furnace is

1. High lagging
2. High leading
3. Low lagging
4. Very low lagging

25. Two individual heater coils are connected to parallel across the mains. If one of the coil break, the other coil 

1. Develops lower temperature
2. Develops same temperature before
3. Develops higher temperature
4. Will also not be heated

26. Furnaces used for cremation use

1. Resistance heating
2. Induction heating
3. Dielectric heating
4. All of the above

27. For heating magnetic materials using induction heating, eddy current and hysteresis losses are respectively proportional to

1. f² and f
2. f and f²
3. f² and f²
4. None of the above

28. The normal voltage used for dielectric heating is

1. 1500 V
2. 15 kV
3. 30 kV
4. 33 kV

29. When a hot-plate is connected to the mains, its element becomes red hot, but the copper wire in the leads remain cool. This is due to

1. The element is coiled, but the copper wire is not
2. Length of the element is more than the copper wire
3. Copper wire is thinner than the element
4. The element has a high resistance than the copper wire

30. A body at temperature T K radiates heat in proportion to

1. T²
2. 1/T²
3. T⁴
4. 1/T⁴