Physics · 7 min read

Ohm’s law: voltage, current, and resistance explained

Use V = IR confidently and understand the assumptions behind basic electrical calculations.

This MayeleCalc guide explains the concept in plain language so you can use the related calculator with better context and confidence. Work through each section, review the practical example, and check the common mistakes before applying the result.

01

Three quantities share one relationship

Voltage equals current multiplied by resistance. Rearranging the equation lets you calculate any quantity when the other two are known.

02

Units communicate meaning

Voltage is measured in volts, current in amperes, and resistance in ohms. Prefixes such as milli and kilo must be converted consistently.

03

Power adds another view

Electrical power can be calculated as voltage multiplied by current. Combining this with Ohm’s law helps estimate device energy use.

04

Real components may differ

Some components do not maintain constant resistance as temperature or voltage changes. Follow specifications and qualified safety guidance.

Practical example

See the idea in action

If a vehicle travels 120 kilometres in 2 hours, its average speed is 120 ÷ 2 = 60 km/h. This represents the full journey, including any slower sections or stops included in the time.

Common mistakes to avoid

  • ×Mixing metres with kilometres or seconds with hours
  • ×Confusing average speed with speed at one instant
  • ×Leaving out direction when the question asks for velocity

Key takeaways

  • Convert units before inserting values
  • Rearrange the equation to match the unknown
  • Check whether the question asks for an average or instantaneous value

Put the idea into practice

Open the calculator library, choose the relevant tool, and compare realistic scenarios using the method from this guide.

Explore calculators →

Continue reading

Related articles