October 5, 2011

Ohm’s Law

We all know that electrons flow through the circuit because of the electromotive force or voltage. Great amount of voltage applied in the circuit will cause more electrons to move from one point to another, or the greater the intensity of the current flowing in the circuit. Connecting resistor with high amount of resistance in the circuit will decrease the intensity of current flow. This relationship between voltage, current and resistance is stated in Ohm’s law.
Ohm’s law is formulated by a German physicist named Georg Simon Ohm. According to Ohm’s law, the electric current flowing through the circuit is directly proportional to the voltage applied in the circuit and inversely proportional to the resistance offered by the circuit. Ohm’s law can be expressed as an equation:

E = IR

  • E is the voltage expressed in volts (V)
  • I is the intensity of current flow expressed in ampere (A)
  • R is the resistance expressed in ohms (Ω)

E=IR can also be written as:

I = E/R  and  R = E/1


The Magic Triangle
The magic triangle can be used to obtain Ohm’s law formula. To get the voltage formula, just put your thumb over “E” on the triangle and you are left with “I” and “R”, which means that the E is the product of I and R (E = IR). For the current (I) formula, just put your thumb over the current symbol and you will have voltage over resistance (I = E/R ). To get the formula for resistance (R), just cover “R” and you are left with the formula voltage divided by current ( R = E/I ).


  1. A circuit has an effective resistance of 1000Ω and the applied voltage of 50V. How much current is flowing through the circuit?

    R = 1000Ω
    E = 50V
    I = ?

    I = E/R
    I = 50volts / 1000 ohms
    I = 0.05 ampere

  2. In a circuit containing a 500Ω resistor, about 0.5A of current is flowing through it. How much voltage is applied in the circuit?

    R = 500 ohms
    I = 0.5 ampere
    E = ?

    E = IR
    E = (0.5amp)(500 ohms)
    E = 250 volts

  3. 3. A circuit containing a 250V potential causes a 0.75A of current flow. What is the resistance of the circuit?

    E = 250 volts
    I = 0.75 amps
    R = ?

    R  =  E/I
    R = (250 volts)(0.75 amp)
    R = 333.33 ohms


GeriLen ELinessete said...

wow, you review me of one of my college subject :P
very informative :)
gah... i miss studying!
what course did/are you taking?

Farida of In Love With Sunflower said...

I think I was absent when this was taught to us :P

Anonymous said...

OMG this is too much for me! Hahahaa!

avagabondmom said...

your post reminded me of how i didn't listen to my teachers in college. shhh. :D i never thought i'd dislike the idea of studying again, but when I saw the equations, then I guess I'd rather go to cooking school!

kath said...

oh my!! that's why i took marketing in college! hehehe!!

Sheng Sheryl Apuhin said...

i'll go with ava na rin...cooking school na lang kami..hahaha..
ayaw ko ng basahin mga pinag susulat mo..hindi ko rin maintindihan..

Luna Longfellow said...

Hahaha! Nice! back to basics.. Im a graduate of ECE so, yeah.. lol!

Mom Michelle said...

Ansabe?! lol! But seriously, what's the Ohm's Law for? ;-)

miekee_18 said...

Just looking at it my brain squeezed hehe..I'll stick to my Nursing career than to compute using those formula.

CC said...

I have no idea how this works... But I'm sure college students will find this post very useful!

Lady Spring said...

*toinks* anu daw?!
Somebody somewhere will probably find this informative. Go go go! :)

Rochelle O. said...

hahaha! I'm not into mathematics! but somehow it may help some :)

verabear said...

I wish I could say I still remember these things, but the truth is, I probably forgot everything after high school!

Oliver Ramos said...

This is really a refresher from our Physics Class way back 5 years ago.. Hehe yeah most of us forgot these things already because sometimes it is not used for our daily lives and we care nowadays on savings and work . Thanks for refreshing this up it brings back old memories of my highschool.

Mae Codizal said...

Haven't forgotten this since highschool :)

Taylor Gilmore said...

OMG, this post took me way back!

Geca Franco said...

I'm sure this will be very helpful to some.

shadz said...

Awesome. That involved a lot of numbers. :(

Allan said...

I used to know this when I was studying my physics. hehehe

Bee said...

This just gave me a headache. @.@

filmansantiago said...

Hmmmm.... yeah, okay?! I see... reactions to a failing physics stud like me?! LOL! kidding, I didn't fail, but almost! :)


Chin chin said...

This is very techie stuff. I used to like this subject but was never my major, so...