# does resistance reduce voltage or just amperage?



## raggie33 (Jul 11, 2004)

i been takeing apart old stuff i have grabing out resisters trying to reduce my voltage to a led but on my meter itt dont show lower voltage is that normal note i have no idea what ohm rateing thease are


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## gadget_lover (Jul 11, 2004)

*Re: does resistance reduce voltage or just ampera*

Rag;

Put the voltmeter leads on each battery. Then put them on either side of the resistor. Now try on each side of the LED.

Given;

3 D cells, 

The first reading will be around 4.5 volts.


The sum (added together) of the last two readings will equal the first.


Resistors "use up" part of the voltage, making less available for the other components. Make the resistance higher and it will comsume a larger portion of the available voltage. 

Resistors also limit the total current that can flow. when in series with the load.

Daniel


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## raggie33 (Jul 11, 2004)

*Re: does resistance reduce voltage or just ampera*

cool thank you gadget


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## Jackal (Jul 11, 2004)

*Re: does resistance reduce voltage or just ampera*

Just remember the formula E=IR (E)Voltage = (I)Current X(R)Resistance ....Therefore.... Resistance and Voltage are inversely proportional and the higher the resistance the lower the current to obtain the same voltage...... or......Use algebra to rearrange the equation and you get E/R=I where you can see the direct inverse relationship between (E)voltage and (R)resistance..... simple OHMS Law /ubbthreads/images/graemlins/thumbsup.gif


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## idleprocess (Jul 12, 2004)

*Re: does resistance reduce voltage or just ampera*

V is used for voltage in most places.


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## Christoph (Jul 12, 2004)

*Re: does resistance reduce voltage or just ampera*

except in ohms law
Chris /ubbthreads/images/graemlins/grin.gif


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## andrewwynn (Jul 12, 2004)

*Re: does resistance reduce voltage or just ampera*

E= 'electromotive force'... the 'v' stands for volt which is the unit used to measure EMF... the formula isn't V = A • ? even though it would make 'sense' from a direct reading 'volts = amps • ohms'. I forget why current is 'i', probably after the guy who discovered it /ubbthreads/images/graemlins/wink.gif

back to topic... in a series circuit the voltage on all the components adds up to the voltage of the source so adding things in will reduce the voltage on all the other parts (even if it's just one.... led)... the higher the resistance the more voltage will be dropped on that particular component... inserting a series resistance will increase the 'total' resistance which will reduce the 'total' current going through the resistor and the led, which is the goal.

another forumula that is key is P=IE... power = current • voltage... once you have a resistor figured out... run that formula to figure out how much power is being consumed by the resistor (turned into heat) because you need a resistor tough enough not to melt... (example: 1/4W, 1/2W, 1W(very big).

have fun, most importantly.

-awr


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