Electrical power loss as heat

[Colin Bell]

Hi John

 

Current can be calculated directly from input voltage and total
resistance (load plus transmission wire)

 

Using I^2xR gives power loss immediately. 

 

To use V^2/R we first need to calculate voltage loss.

Voltage loss can't be calculated initially, since we don't know current
initially, so we have to do that anyway.

Once current is calculated, voltage loss is calculated from Ohm's
Equation, V= IxR(line)

Using V^2/R now gives the power loss.

Takes longer!

 

Cheers

 

Colin

Colin Bell

Futureintech Facilitator Christchurch


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________________________________

From: phys-teach-talk-bounces at nzip.org.nz
[mailto:phys-teach-talk-bounces at nzip.org.nz] On Behalf Of John Watson
Sent: Monday, 11 August 2008 10:24 a.m.
To: Physics discussion group
Subject: Electrical power loss as heat

 

Hi

 

When looking at power lost as heat in transmission lines, can someone
please explain why we use P=i^2R but cannot use P=V^2/R? Aren't they
equivalent expressions?

 

thanks

_________________________________________
John Watson
St Bede's College
Christchurch

 

E-Mail: jwatson at stbedes.school.nz

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