Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

This is an AMP page - Open full page! for all features.

Ohm's Law

Voltage, current and resistance

Sponsored Links

Ohm's law states that

"the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them".

Ohm's law can be expressed as 

I = U / R                     (1)

where 

I = current (ampere, A)

U = electrical potential (volts, V)

R = resistance (ohms, Ω)

Example - Ohm's law

A 12 volt battery supplies power to a resistance of 18 ohms. The current in the elctrical circuit can be calculated as

I = (12 volts) / (18 ohm)

    = 0.67 ampere

Equivalent Expressions of Ohm's Law

Ohm's law (1) can also be expressed as

U = R I                         (2)

or 

R = U / I                       (3)

Download and print the Ohm's Law diagram!

Example - Electric Circuit Resistance

A current of 1 ampere is flowing through a 230 V electric circuit. From the diagram above this indicates resistance 

R ≈ 220 Ω

This can alternatively be calculated with Ohm's law

R = (230 V) / (1 A)

   = 230 Ω

Example - Ohm's Law and Multiples and Submultiples

Currents, voltages and resistances in electric circuits may often be very small or very large - so multiples and submultiples are often used. 

The voltage required applied to a 3.3 kΩ resistor to generate a current of 20 mA can be calculated as

U = (3.3 kΩ) (1000 Ω/kΩ) (20 mA) (10-3 A/mA)

   = 66 V

Electric Resistance Nomogram

Download and print the Electric Resistance vs. volt and ampere nomogram!

The default values in the nomogram above indicates 230 volts, resistance 24 ohm and current 10 amps.

Power

Electric power can be expressed as 

P = U I

  = R I2 

  = U2 / R                     (4)

where 

P = electrical power (watts, W)

Example - Power Consumed

The power consumed in the 12V electrical circuit above can be calculated as

P = (12 volts)2 / (18 ohm)

   =  8 W

Example - Power and Electrical Resistance

A 100 W electric light bulb is connected to a 230 V supply. The current flowing can be calculated by reorganizing (4) to

I = P / U

  = (100 W) / (230 V)

  = 0.43 ampere

The resistance can be calculated by reorganizing (4) to

R = U2 / P

   = (230 V)2 / (100 W) 

   = 529 Ω

Electric Power Nomogram

This nomogram can be used to estimate power vs. voltage and ampere.

  Download and print the Electric Power vs. volt and ampere nomogram!

The default values in the nomogram above indicates 240 volts, resistance 10 amps and power 2.4 kW for DC or single phase AC - and 4 kW for three phase AC. 

Sponsored Links

Related Topics

Related Documents

Sponsored Links

Share

Search Engineering ToolBox

  • the most efficient way to navigate the Engineering ToolBox!

SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro .Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!

Privacy

We don't collect information from our users. Only emails and answers are saved in our archive. Cookies are only used in the browser to improve user experience.

Some of our calculators and applications let you save application data to your local computer. These applications will - due to browser restrictions - send data between your browser and our server. We don't save this data.

Google use cookies for serving our ads and handling visitor statistics. Please read Google Privacy & Terms for more information about how you can control adserving and the information collected.

AddThis use cookies for handling links to social media. Please read AddThis Privacy for more information.

Topics

Unit Converters

Temperature

oC
oF


Load Calculator!

Length

m
km
in
ft
yards
miles
naut miles


Load Calculator!

Area

m2
km2
in2
ft2
miles2
acres


Load Calculator!

Volume

m3
liters
in3
ft3
us gal


Load Calculator!

Weight

kgf
N
lbf


Load Calculator!

Velocity

m/s
km/h
ft/min
ft/s
mph
knots


Load Calculator!

Pressure

Pa (N/m2)
bar
mm H2O
kg/cm2
psi
inches H2O


Load Calculator!

Flow

m3/s
m3/h
US gpm
cfm


Load Calculator!

9 20

This website use cookies. By continuing to browse you are agreeing to our use of cookies! Learn more