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You have seen that if a certain current flows in a circuit, it flows because a certain electromotive force & that the amount of current is limited by the resistance of the circuit. The amount of current depends upon the amount of electrical pressure & amount of resistance. This fact was discovered by a George S. Ohm & now it is famous as Ohm’s law which is the fundamental equation of an electrical science. Since it was first started in 1827. Ohm’s law is that the current flowing in a circuit is directly proportional to the applied voltage and inversely proportional to the resistance. Following formula’s used to find out current, resistance, voltage.
Where, I = Current, in ampere E = Voltage, in volt R = Resistance, in Ohm An aid to remembering the Ohm’s law relationship is shown in the divided triangle. If you know the voltage & resistance of the circuit, you can find out current, then by simply applying the following equation -
Ex - 1.
A 100 Ohms resistance is connected across 230 volts DC.Supply. Calculate the current flowing through the circuit? Ans- Given- E = 230 V. R = 100 Ohms ...Ans.
If you know resistance & current of the circuit, you can find out voltage, by applying the following equation - E = I ´ R
Ex - 2.
A current of 5 ampere of flowing through resistance, Calculate supply voltage? Ans- Given I = 5A R = 50 Ohms E = I ´ R = 5 ´ 50 = 250 Volts E = 250 Volts ...Ans. If you know the voltage & current of the circuit, you can find out resistance by applying the following equation -
Ex - 3.
A resistance is connected across 230 volts DC supply if current passing through the resistance is 12.5 ampere. Calculate the value of resistance? Ans- Given I = 12.5 ampere E = 230 Volts
R = 18.4 Ohms ...Ans. Intext Question 5.1
(A) Fill in the blanks:
1. Fuse is a device. 2. Lamp is a device which converts energy in to.........energy.
3. In simple circuit power source device & device & device are used. 4. A complete path of electrically current is circuit. (
B) State True or False:
1. The lamp is the power source. 2. Piano type switch are used as controlling device. 3. In a close circuit current flows from positive terminal of source to the negative terminal of source through given resistance. 4. The relationship between voltage, current, resistance is given ohm’s law. 5. To find out infinity value of current flowing through circuit then ohm’s law used.
(C) Match the pairs
a) Voltage 1) Switch b) Current 2) Volts c) Resistance 3) Fuse d) Controlling device 4) Ohm e) Safety device 5) Ampere
Law of Resistance
You have seen that the current flowing through the circuit depends upon voltage & current. Now we are going to see on which factors resistance depends, these factors are known as laws of resistance. 1. The resistance of the conductor to varies directly with its length. The longer length, greater the resistance, shorter the length, lower the resistance. 2. The resistance of the conductor is inversely proportional to its cross-sectional area. The larger cross sectional area of a conductor, smaller the resistance & the smaller cross-sectional area, higher the resistance. 3. The resistance of the conductor depends upon the material. Each material offers a different resistance to the movement of electrons. Silver, Copper, Gold, Aluminum material has low resistance, with respective its resistance. 4. The resistance of conductor depends on the temperature of the conductor. At higher or lower temperature, the resistances of all material changes. In most cases, the temperature of a material goes up, its resistance also goes up, but with some other material, increased heat causes the resistance to go down the amount that resistance is affected by each degree of temperature changed is called temperature co-efficient.
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