Check the dimensional correctness of P = I²R
Power dissipated in a resistor. The heat produced per second when current I flows through a resistance R.
Equation checker
Matching dimensions are necessary, not sufficient. A check cannot see pure numbers such as 1/2 or 2π, so a consistent equation can still be wrong.
P = I2 RP[M L2 T-3]=I2 R[M L2 T-3]Step by step
1. What each symbol stands for
- P power [M L2 T-3]
- I electric current [A]
- R electrical resistance [M L2 T-3 A-2]
2. The dimensions of each term
- P [M L2 T-3] [M L2 T-3]
- I2 R [A]2 × [M L2 T-3 A-2] [M L2 T-3]
3. Compare
Every term has dimensions [M L2 T-3], so the equation is dimensionally consistent.
What it proves and what it does not
It can show
- Every term that is added or subtracted has the same dimensions, so the sum makes sense.
- Both sides of the equals sign have the same dimensions.
- Angles inside sin, cos and similar functions are pure numbers.
It cannot show
- A pure number such as 1/2 or 2π has no dimensions, so a check cannot see a missing or wrong one.
- Two quantities with the same dimensions, such as work and torque, cannot be told apart.
- A sign error or a wrong power that keeps the dimensions equal goes unnoticed.
Matching dimensions are necessary but not sufficient. Pure numbers such as 1/2 or 2π have no dimensions, so a check cannot see them, and an equation with matching dimensions can still be wrong.
Look up each quantity
P = I²R: quick answers
Is P = I²R dimensionally correct?
Yes. Every term has the same dimensions, [M L² T⁻³], so P = I²R is dimensionally consistent. That does not prove the equation itself is correct.
Does a dimension check prove P = I²R is right?
No. A check can show that an equation is wrong, but it cannot show that it is right. Pure numbers such as 1/2 and 2π have no dimensions, so the check cannot see them.