Percent Error

a group of students in a science lab In a laboratory situation, you often compare a measurement that you take in an experimental situation with a theoretical value, a value that is calculated from equations or found in a reference guide. The measured value is called the experimental value. When you are comparing those two values, you use the percent error equation.

Percent Error

Percent Error = $\mathsf{ \frac{\vert\text{Experimental value - Theoretical value}\vert}{\vert\text{Theoretical value}\vert }}$ •100

See if you can answer the questions below using the percent error formula.

Question

Phillip knows that it should take a ball 0.64 seconds to fall 2 meters, but when he measured the fall, he got 0.66 seconds. What is the percent error in his experiment?

Percent Error = $\mathsf{ \frac{\vert\text{Experimental value - Theoretical value}\vert}{\vert\text{Theoretical value}\vert }}$ •100

Percent Error = $\mathsf{ \frac{\vert\text{0.66 - 0.64}\vert}{\vert\text{0.64}\vert }}$ •100

Percent Error = 3.13%

Question

Shanda measured the density of a block to be 4.56 g/cm³. The actual density of the block is 4.74 g/cm³. What is the percent error in her measurement?

Percent Error = $\mathsf{ \frac{\vert\text{Experimental value - Theoretical value}\vert}{\vert\text{Theoretical value}\vert }}$ •100

Percent Error = $\mathsf{ \frac{\vert\text{4.56 - 4.74}\vert}{\vert\text{4.74}\vert }}$ •100

Percent Error = 3.80%

How do you compare experimental and theoretical values of a measurement?

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