Ohm's Law

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This is a very important thing to know if you're looking to get into electronics.
 Ohms is the measurement used for the amount of resistance of a resistor.

Step 1: The Formula


Is the formula which is Ohm's law. According to this formula, V=IR, I=V/R, and R=V/I.
V means voltage, I means current, and R means resistance. So, Voltage equals Current times Resistance. To remember this, here is Ohm's Pyramid

Step 2: To Make It Easier

In case you don't understand yet, here is an example:

You want to find the amount of ohms of resistance you need to power a device that uses
40mA (Milliamps) with a nine volt battery.

All you have to do is divide voltage(9) by Amps (in this case, milliamps(40(in amps it's 0.04))) So, it would be like this:


Step 3: Bonus

Here is a cool thing i seen on you tube.
You can make your own resistor just by drawing a rectangle on paper!
This is true, and you can do it too!(lol nice slogan huh?)

Just draw a really, REALLY dark rectangle on a piece of paper about two centimetres long(with a HB2 pencil). Then take a nine volt batery with a battery clip, hook the red wire(+) to the longer lead of an led(+) and touch the shorter lead of the led(-) to one end of the rectangle, and the black wire of the clip(-) to the other end of the rectangle.

The led should light up. Also, what's even cooler is, the closer the black wire and the led, the brighter it is!

***Do NOT touch the battery directly to the led. It will burn out, and possibly explode.

For people making synthesizers and piano thing with 500k pots, a dark hairline(~0.5mm thick) ~4.5cm long is 500k



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    12 Discussions


    3 years ago

    THANK YOU !!!!!!!


    7 years ago on Step 3

    LED's do not explode.. Atleast not from my experience of blowing LED's out....
    If you are running a high-joule capacitor bank through a tiny LED, yes, good chance that it will explode.

    If LED's were able to explode, I would have made LED bombs long ago. :) Thanks for the tutorial.

    5 replies

    Reply 7 years ago on Step 3

    Ahah glad you liked it, but I guess I was kind of over-exaggerating about the "explode" part ;P


    Reply 7 years ago on Step 3

    Actually, you did do a good job explaining it! Thanks for the instructable! :P


    Reply 7 years ago on Introduction

    It's good. I'm 16, congratulations, and keep writing instructables... Im actually researching the mathematics and construction of electromagnetic coils. I am trying to accomplish a 2-3 tesla magnet.. The biggest magnet in the world is over 50 tesla.. To see how much one tesla is, compare the strongest neodemium magnet you can find. That's one tesla in strength.

    Just think. Mine will be over 1 tesla. (Preferably 2 tesla)

    Anyway. I learned something.


    8 years ago on Introduction

    This is an amazing thing that I learnt about 3 months ago, but I learnt even more when I had a look at this ible!


    8 years ago on Introduction

    I'm 72 years old & I find this very interesting but wonder why so few people know how to spell. (The word remember in the formula is incorrectly spelled).

    1 reply

    8 years ago on Introduction

    the r=v/i can be used in all areas of math and is a VERY useful tool to understand