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To calculate the currents ir1 and ir2 in a parallel circuit of two resistors r1 and r2, consider the voltage across them. By Kirchoff's voltage law, the voltage across each resistor will be the same, so simply use Ohm's law to divide voltage by each resistor to get each resistor's current.
ir1 = v / r1
ir2 = v / r2
If you don't know voltage, but you do know total current, then determine the total resistance as RT = R1R2/(R1+R2), calculate voltage as ITRT and proceed from there.
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The voltage in a battery is 9 volts. The resistance is 3 ohms. What is the current?
There are a couple of ways to work this one. You can find the so-called branch currents (the current through each resistor) and then add them to get total current, or you can find the total effective resistance and then apply that information to the applied voltage to compute total current. Let's do this. I = E/R for each resistor. IR1 = E/6 = 9/6 = 3/2 = 1 1/2 amps IR2 = E/3 = 9/3 = 3 amps Itotal = IR1 + IR2 = (1 1/2) + (3) = 4 1/2 amps That's one way. Here's the other. Rtotal = 1 / [(1/R1) + (1/R2)] = 1 / [(1/6) + (1/3)] = 1 / [(1/6) + (2/6)] = 1 / [3/6] = 2 ohms Itotal = Eapplied / Rtotal = 9 volts / 2 ohms = 4 1/2 amps It checks. What a surprise. Ohm's law is correct.
Why is it economical to use high voltages for the transmission of electrical power?
Followings are few reasons. 1. At high voltage for the same power, value of current will be less. 2.If less current in line then less transmission loss(IR2) will occur,which will again save money. 3.If the current will be less then less size of conductor will be required and will save money. 4.If less size then less weight and less strength of poles will be required which will again save money. I hope will these reasons you can understand the fact.
