Ques-1 How much current will an electric bulb draw from 220 V source if the resistance of the bulb is 1200 ohm ? If in place of bulb, a heater of resistance 100 is connected to the sources calculate the current drawn by it?
Ans-1 According to ohm's law we know that I=VR: I=220*1200= 264000 ampere.
(2)If heater is placed instead of bulb then current will be: I=VR,I=220*100=22000 ampere.
Ques-2 Define electric power.
(b) An electric bulb is connected to a 200 V generator. The current is 0.5 A. What is the power of the bulb ?
Ans-2 (a) ELECTRIC POWER--- Electric power is defind as the amount of electric energy consumed in a circuit per unit time.
(b)we know P=V/I=200/0.5=400 watt.
Ques-3 A resistance wire is stretched to double its length . How will its resistance change ?
Ans-3 we know, R=pl/a (1)
When wire is pulled, its lenth increases and area of cross-section decreases i.e,wire becomes thin but volume of wire remains the same.
new lenth, l'=2l
new area, A=A'
since original volume of wire=new volume
Al=A'l' orAl=A'*2l
or A'=A/2
New resistance, R'=pl'/A'=p82l/A/2=4pl/A (2) Dividing (1) and (2). we get R'=4R
Thus the new resistance of wire = 4 times its original resistance.
Ques-4 Explain the function of fuse in a domestic electric circuit ? An electric oven having power rating 2000 W, 220V is used in an electric circuit, having a fuse of 5A rating. What is likely to happen when the oven is switched on ? Explain.
Ans-4 Fuse is a safety devicee connected in series with the electric circuit.Electric fuse is a wire made of a material whose melting point is very low. For example-of the material of making fuse wire are copper or tin-lead alloy.
A current flows in the circuit and hence through the fuse wire, a large amount of heat is producced due to this large amount of heat, the fuse wire melts and the circuit will break so that current stops flowing in the circuit. this saves the electric circuit from burning.
Ques-5 An electric heater rated 800 W operates 6 h/day. Find the cost of energy to operate it for 30 days at ` 3.00 per unit.
Ans-5 Energy consumed by electric heater in one day: 800w*6h=4800wh=4.8kwh
Energy consumed in 30 days=4.8*30=144units
cost of one unt = rs3.00
cost of 144units=144*Rs3.00=432
So electricity bill of 30 days is Rs 432
Ques-6 Why element of electrical heating devices are made up of alloys?
Ans-6 They are made up of alloys because alloys have more melting point .since wires are made up of nichrome which is the alloy of metal.the resistivity of nichrome is more than the resistivities of metal used to make it. hence nichrome does not burneven at high temperature.the melting point of nichrome is 1500`c.That is why heating elements are made up of an alloy that is an alloy.
Ans-1 According to ohm's law we know that I=VR: I=220*1200= 264000 ampere.
(2)If heater is placed instead of bulb then current will be: I=VR,I=220*100=22000 ampere.
Ques-2 Define electric power.
(b) An electric bulb is connected to a 200 V generator. The current is 0.5 A. What is the power of the bulb ?
Ans-2 (a) ELECTRIC POWER--- Electric power is defind as the amount of electric energy consumed in a circuit per unit time.
(b)we know P=V/I=200/0.5=400 watt.
Ques-3 A resistance wire is stretched to double its length . How will its resistance change ?
Ans-3 we know, R=pl/a (1)
When wire is pulled, its lenth increases and area of cross-section decreases i.e,wire becomes thin but volume of wire remains the same.
new lenth, l'=2l
new area, A=A'
since original volume of wire=new volume
Al=A'l' orAl=A'*2l
or A'=A/2
New resistance, R'=pl'/A'=p82l/A/2=4pl/A (2) Dividing (1) and (2). we get R'=4R
Thus the new resistance of wire = 4 times its original resistance.
Ques-4 Explain the function of fuse in a domestic electric circuit ? An electric oven having power rating 2000 W, 220V is used in an electric circuit, having a fuse of 5A rating. What is likely to happen when the oven is switched on ? Explain.
Ans-4 Fuse is a safety devicee connected in series with the electric circuit.Electric fuse is a wire made of a material whose melting point is very low. For example-of the material of making fuse wire are copper or tin-lead alloy.
A current flows in the circuit and hence through the fuse wire, a large amount of heat is producced due to this large amount of heat, the fuse wire melts and the circuit will break so that current stops flowing in the circuit. this saves the electric circuit from burning.
Ques-5 An electric heater rated 800 W operates 6 h/day. Find the cost of energy to operate it for 30 days at ` 3.00 per unit.
Ans-5 Energy consumed by electric heater in one day: 800w*6h=4800wh=4.8kwh
Energy consumed in 30 days=4.8*30=144units
cost of one unt = rs3.00
cost of 144units=144*Rs3.00=432
So electricity bill of 30 days is Rs 432
Ques-6 Why element of electrical heating devices are made up of alloys?
Ans-6 They are made up of alloys because alloys have more melting point .since wires are made up of nichrome which is the alloy of metal.the resistivity of nichrome is more than the resistivities of metal used to make it. hence nichrome does not burneven at high temperature.the melting point of nichrome is 1500`c.That is why heating elements are made up of an alloy that is an alloy.
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