What are the common errors in measuring length with a metre ruler?

Common errors in measuring length with a metre ruler include parallax error, zero error, and incorrect positioning of the ruler.

Parallax error is a common mistake that occurs when the observer's eye is not directly above the measurement mark on the ruler. This can cause the measurement to appear shorter or longer than it actually is. To avoid this error, always ensure that your eye is directly above the point you are measuring. This is particularly important when measuring small lengths where a slight shift in viewing angle can significantly affect the measurement.

Zero error is another common mistake. This happens when the zero mark on the ruler is not exactly at the edge of the object being measured. For instance, if the zero mark is slightly worn out or not clearly visible, it can lead to inaccurate measurements. Always ensure that the zero mark on the ruler aligns perfectly with the edge of the object you are measuring.

Incorrect positioning of the ruler can also lead to measurement errors. This usually happens when the ruler is not perfectly aligned with the length being measured. For example, if you are measuring the length of a table, the ruler should be perfectly parallel to the edge of the table. If it is tilted or skewed, the measurement will be inaccurate.

Lastly, it's important to remember that a metre ruler has a certain level of uncertainty, usually up to half a millimetre. This is due to the finite width of the lines marking the measurements on the ruler. Therefore, even with perfect technique, there will always be a small level of uncertainty in any measurement made with a metre ruler.

IGCSE Physics Tutor Summary: When measuring length with a metre ruler, avoid common mistakes like parallax error by keeping your eye directly above the measurement, zero error by ensuring the zero mark aligns with the object's edge, and incorrect ruler positioning. Remember, due to the thickness of the measurement lines, there's always a slight uncertainty, usually up to half a millimetre, in any measurement.