Register to reply

Electricity- Power dissipation formula question

by cambalacus
Tags: dissipation, electricity, formula, power
Share this thread:
cambalacus
#1
Jun20-09, 10:43 AM
P: 1
1. The problem statement, all variables and given/known data
while surfing the internet i stumbled upon the following question:
Why ac(alternating current) is used to power houses instead of DC?

Answer:The answer lies in the transmission lines for the electricity. The wires have a defined resistance, and when current passes through them there is a power loss given by
W (power) = I (current) squared x R (resistance)

Clearly, lowering the current reduces the power loss considerably. The power transmitted is given by
W = V (voltage) x I, so we could multiply the voltage by 100, reduce the current by 100, transmit the same power, and reduce the loss in the wires by 10000.
This high voltage is desperately unsafe in the domestic situation, so it must be reduced. Reducing DC is very difficult, so it is much easier to use AC.

2. Relevant equations
How can one lower the current without lowering the voltages and, at the same time,without changing the resistance of the wires?
Phys.Org News Partner Science news on Phys.org
Mysterious source of ozone-depleting chemical baffles NASA
Water leads to chemical that gunks up biofuels production
How lizards regenerate their tails: Researchers discover genetic 'recipe'
rl.bhat
#2
Jun20-09, 11:09 AM
HW Helper
P: 4,433
Please go through the principle of step up and step down transformer.
negitron
#3
Jun20-09, 11:55 AM
Sci Advisor
negitron's Avatar
P: 842
Power must be conserved so that power in must equal power out (taking into account losses). Since power, in its simplest form, equals current multiplied by voltage you can readily see what must necessarily happen to the voltage when the current is reduced.

There's your answer.


Register to reply

Related Discussions
Dissipation, resistance, and power. Introductory Physics Homework 1
Dissipation of Power by Resistors Introductory Physics Homework 3
Power dissipation Introductory Physics Homework 3
Power dissipation Introductory Physics Homework 1
Power Dissipation Introductory Physics Homework 1