Electrical Work Power and Energy - Short Question and Answer

Electrical Work Power and Energy - Short Question and Answer Points : electrical work power and energy short question and answer Q. 1. The element of heater is very hot as the wires carrying current are cold. Why? Ans : Element of heater is made of nichrome as wires carrying current are prepared of aluminium/copper. The resistance of nichrome is extremely high as compare to that of copper/aluminium. While it is a series circuit, heat produced (H = I² Rt) depends only upon resistance of conductor in this case. Thus the element of heater is extremely hot due to its high resistance as the lead wires are cold due to their short resistance. Q. 2. What do you signify by safe value of fuse wire current? Ans : It is highest value of current that a fuse wire can carry with no getting melted. Under such conditions, rate of production of heat in fuse wire is equivalent to rate of failure of heat. Q. 3. What is difference between heating-wire and fuse wire? Ans : A heating-wire is use in heating use while a fuse wire is use in a circuit to protect it as of an overload. Thus, melting point of material of heating-wire is high as melting point of a fuse wire is low. Q. 4. Two bulbs, one of 60 W and other of 100 W, have similar voltage rating are linked in series across supply in a room. Which bulb will glow brighter? if one of bulbs is switched off what will be the cause on illumination? Ans : The 60 W bulb has additional resistance (R = V²IP) than that of 100 W bulb. Thus, when two bulbs are linked in series, rate of dissipation of energy P(= 1²R; I is same) is more in that bulb which has larger resistance. Thus, 60 W bulb will burn brighter. When one of the bulbs is switched off the circuit resistance decreases and hence current increases. As a result, rate of debauchery of energy P (= I²R) increases. Therefore, total light in the room will amplify. Q. 5. The nichrome heater consumes 1.5 kW and heats up to a temperature of 750° C. A tungsten bulb working at similar voltage operates at a much higher temperature of 1600° C in order to emanate light. Does it mean that tungsten bulb consume more power? Ans : Not inevitably. The stable temperature attain through a resistor depends not only on power consumed but moreover on its characteristics (e.g., surface area, emissivity, etc.) which decides heat loss due to radiation. Q. 6. The wires supply current to an electric bulb are not hew while the filament of bulb becomes as hot. Explain. Ans : Resistance of wires per unit length is small as compare to that of filament of bulb. As a result, the rate of production of heat in wires is so small to source any visible cable rise of temperature. On the other hand, rate of heat production in bulb is extremely high. Thus, the filament becomes white hot. Q. 7. What are important characteristics of a fuse? Ans : A fuse has four important characteristics viz
(i) physical size (ii) current rating (iii) voltage rating and (iv) fusing characteristic
Current rating of a fuse must be more than maximum normal circuit current by 25%.
Voltage rating of fuse must be at least equivalent to circuit voltage. The fusing characteristic is resolute by blowing-time versus current flow graph. Q. 8. What are special characteristics of a heating element? Ans : Heating element has to have high resistance and high melting point. Q. 9. What is require of an electric fuse? Ans : An electric circuit require a fuse for overcurrent protection. While short circuit occurs in a circuit an unusually high current flows which can make high power dissipation and elevated temperature. This can reason severe equipment damage and might even start a fire. The wire in a building can get hot sufficient to ignite structural materials. Note that wires do contain a few resistance and power dissipated in resistance (P = I² R) varies as the square of current. If current doubles, the power dissipation increases four times. A fuse is a weak circuit component that opens when he current reaches a dangerous level.