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NCERT Class XII Chapter
Current Electricity
Questions With Solutions

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Question : 4 of 24
Marks: +1, -0
(a) Three resistors 2 Ω, 4 Ω and 5 Ω are combined in parallel. What is the total resistance of the combination?
(b) If the combination is connected to a battery of emf 20 V and negligible internal resistance. Determine the current through each resistor, and the total current drawn from the battery.
Solution:  
(a) Total resistance of the combination in parallel
1Req\frac{1}{R_{eq}} = 1R1+1R2+1R3\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3} or 1Req\frac{1}{R_{eq}} = 12+14+15\frac{1}{2}+\frac{1}{4}+\frac{1}{5} or ReqR_{eq} = 2019\frac{20}{19} = 1.05 Ω
(b) Potential of 20 V will be same across each resistor, so current
I1I_1 = VR1\frac{V}{R_1} = 202\frac{20}{2} = 10 A
I2I_2 = VR2\frac{V}{R_2} = 204\frac{20}{4} = 5 A
I3I_3 = VR3\frac{V}{R_3} = 205\frac{20}{5} = 4 A
Total current drawn from the cell,
I = I1+I2+I3I_1+I_2+I_3 or I = 19 A
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