MadSci Network: Engineering

Re: How much power is supplied in a home socket

Date: Tue Jul 25 05:32:01 2000
Posted By: Jonathan Feldman, Undergraduate, Applied Chemistry, University of Technology, Sydney
Area of science: Engineering
ID: 961091765.Eg

I think you have slightly confused the use of the word "POWER".

POWER is the product of the voltage across a component (say, the television), 
and the current (measured in amps) flowing through that component.

The voltage supply to our houses is usually constant (here in Australia, it is 
240V, it may be different where you are).  Hence, the POWER usage of the TV is 
proportional to the CURRENT 
drawn by the TV.

The CURRENT drawn by a component my vary, for example, the TV might draw 2 amps, 
whilst the video player might only draw 0.5 amps.  The TV uses 4 times more 
CURRENT than the video, and hence uses 4 times more POWER.

Now, let's go back to the battery for a moment.  When you attach a bulb, then 
attach a second bulb in parallel, the bulbs don't go dimmer.  But start to 
attach 3, 4 or more bulbs in parallel, and they start to dim a bit.  This is 
because each bulb is trying to draw, say, 100 mA, so the total current 
requirement of 4 bulbs is 400 mA.  But the battery can only supply 200 mA (say) 
at its rated voltage.  After this, a property of the battery called INTERNAL 
RESISTANCE comes into effect, and the voltage of the battery starts 

Your home power socket does not exhibit this effect (or at least, you would have 
to draw a HUGE amount of current to see it - several thousand amps, probably).  
When you use an adaptor, the sockets on the adaptor are also in parallel, so 
this is why you can plug lots of devices into an adaptor, and the socket can 
supply enough power.

Jonathan Feldman
University of Technology, Sydney

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