What is the formula for efficiency in physics

The formula for efficiency ($\eta$) in physics is the ratio of useful output energy (or power) to the total input energy (or power). It is often expressed as a percentage.

$$\eta = \frac{\text{Useful Output Energy}}{\text{Total Input Energy}} \times 100\%$$

or

$$\eta = \frac{\text{Useful Output Power}}{\text{Total Input Power}} \times 100\%$$

In terms of symbols:

$$\boxed{\eta = \frac{E_{\text{out}}}{E_{\text{in}}} \times 100\% \quad \text{or} \quad \eta = \frac{P_{\text{out}}}{P_{\text{in}}} \times 100\%}$$

Where:

• $\eta$ is the efficiency.
• $E_{\text{out}}$ is the useful output energy.
• $E_{\text{in}}$ is the total input energy.
• $P_{\text{out}}$ is the useful output power.
• $P_{\text{in}}$ is the total input power.