Use of Resistance

139

01:28:59

Use of resistance, For drop extra.

Example:
We need 3v from 5v battery.
Extra voltage drop down using resistance. .. 
And
using ohm's low formula ... V=IR

Content for experiment
Buttery - 5v
LED - 3V. 30ma
Resistance - 33.3ohm's

published 11 years ago

Sine_eyed

11 years ago

You're close, but incorrect. The resistor limits current, not dropping voltage. The LED does that. Your Ohm's Law calculation should be: ( Vsource - Vdrop ) / Iled= R .... So we have (5v-3V)/30mA .... Which is 2V/.03A=66.667Ohms so your resistor should have the value 66.7

Sine_eyed

11 years ago

Whoops- not you hurz, sorry I didn't see you'd already commented..

RahulJha

11 years ago

Sir (sine_eyed), Software showing in a corner, Resistor drop the voltage 5v to 3v. (What is this Sir...?) . Thank you for comment on my Circuit.

Sine_eyed

11 years ago

Actually it shows 3.1V and that is sure to the value of the Current Limiting Resistor, along with the Forward Voltage of the LED. Did you try a 66.7ohm resistor? Try that and you well see exactly 3V at the anode, and 30mA through the LED.

Sine_eyed

11 years ago

Or try changing the value of the LED back to 20mA, (or any other value) and see what happens to the voltage...

RahulJha

11 years ago

Thanks.. Sine_eyed...

RahulJha

11 years ago

Can you send me ... how to calculate ohm using vold and ampire. .. exactly.

Sine_eyed

11 years ago

Certainly. First I'd like to point out that Ohm's Law is not just a single equation that solves everything! Using algebra it can be transposed every which way when calculating voltage, resistance, amperage and power. So, you were not entirely incorrect, you just used the wrong part of the equation. I.e.- you needed to find 'R', but you calculated to find 'V'. But you already know V, as it comes from the source. You also know the LED wants to draw 30mA (.03A) ideally, so you needed to find the correct resistance to limit the current to the known value. Your equation should have been: R=V/I

wyoelk

11 years ago

See the Examples tab for more info on Ohms law and the App. Great job @sine on the explaney part

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