Re: Alternating Current



"Lorraine" <lorrainewinters80@xxxxxxxxx> wrote in message
news:1116858671.276400.165860@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

> Suppose in a DC (Direct Current) circuit with 10 volts source
>and 1 ampere. Is there a difference in the current in the wires
>if you use a resistor of 10 ohm vs a 10 ohm load (such as a
> light bulb)?

There would be very little difference (10 Ohms is 10 Ohms). However light
bulbs aren't perfect resistors. The resistance varies with temperature so as
the bulb heats up the current falls.

>Does the value of the resistor stand for the amount
>of current the load needs??

Essentially yes.

> Does this mean heavier
>load such as dc motors has lesser resistance and
>more current?

I would forget motors for the moment. Just think about resistors... What you
say is a very good way to think of a load/resistor. I like to think of the
load "sucking" the current out of the supply. The lower the resistance the
more current it sucks out of the supply. The equation is I = V/R so the
smaller R is the bigger I gets. It's interesting to work out what happens if
you replace a resistor with a big fat wire which has nearly zero resistance.

On the other hand I like to think of voltage sources (batteries, power
supplies etc) "pushing" current into the load. eg the higher the voltage the
more current is pushed through the load. The same equation I = V/R .... Now
think what happens if V is made large, very large.

DC Motors are much more complicated than they look and don't make good
examples for beginners. A motor converts electrical energy into mechanical
energy. The current/energy drawn (sucked) from the power supply depends on
the mechanical load connected to the motor. Think about a food mixer. Put
water in it and very little energy is needed. Put bread dough in it and it
tries hard to go at the same speed but draw more current. A perfect motor
would convert ALL the electrical energy into mechanical energy but real
motors aren't perfect. The copper windings have some resistance and this
causes energy to be lost as heat.




.

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