# How to calculate percent error Physics

When you calculate results that are aiming for known values, the percent error formula is useful tool for determining the precision of your calculations. �The formula is given by:T

When you calculate results that are aiming for known values, the percent error formula is useful tool for determining the precision of your calculations. �The formula is given by:

The experimental value is your calculated value, and the theoretical value is your known value. �A percentage very close to zero means you are very close to your targeted value, which is good. �It is always necessary to understand the cause of the error, such as whether it is due to the imprecision of your equipment, your own estimations, or a mistake in your experiment.

**Example**: �

The 17th century Danish astronomer, Ole R�mer, observed that the periods of the satellites of Jupiter would appear to fluctuate depending on the distance of Jupiter from Earth. �The further away Jupiter was, the longer the satellites would take to appear from behind the planet. �In 1676, he determined that this phenomenon was due to the fact that the speed of light was finite, and subsequently estimated its velocity to be approximately 220,000 km/s. �The current accepted value of the speed of light is almost 299,800 km/s. �What was the percent error of�R�mer's estimate?

**Solution**:

experimental value = 220,000 km/s = 2.2 x 108 m/s

theoretical value = 299,800 km/s 2.998 x 108�m/s

So�R�mer was quite a bit off by our standards today, but considering he came up with this estimate at a time when a majority of respected astronomers, like Cassini, still believed that the speed of light was infinite, his conclusion was an outstanding contribution to the field of astronomy.