Short Answer:

Parallax error is a type of observational error that occurs when the position of the observer’s eye is not aligned properly with the scale of a measuring instrument. This causes the reading to appear higher or lower than the actual value. It usually happens in instruments with pointer-type scales like analog voltmeters or ammeters.

To avoid parallax error, the observer should always look straight at the pointer from the front, not from an angle. Some instruments have a mirror behind the pointer to help align the eye correctly. When the pointer and its reflection line up, the reading is accurate.

Detailed Explanation:

Parallax Error

In electrical and physical measurements, correct observation of readings is very important. One common source of mistake in analog instruments is parallax error. This happens when the reading on the scale appears to change depending on the angle from which it is viewed. Understanding and avoiding this error helps ensure accurate and reliable measurements.

Meaning of Parallax Error

Parallax error occurs when the observer’s eye is not directly in line with the pointer and the scale of a measuring device. Because of this misalignment, the pointer seems to be at a different position on the scale than it actually is. This error is caused by the gap between the pointer (needle) and the scale, especially in analog instruments.

For example, if you look at a voltmeter from the side instead of from the front, the pointer might appear to show 220V when it is actually at 215V. This small mistake can affect calculations and outcomes, especially in sensitive circuits.

Causes of Parallax Error

1. Viewing from an angle
   When the observer’s eye is not perpendicular to the scale, the pointer appears displaced.
2. Lack of mirror scale
   Instruments without mirrors behind the pointer make it harder to judge the correct position.
3. Wide gap between pointer and scale
   The larger the distance between the pointer and the scale surface, the greater the parallax effect.

Where Parallax Error Commonly Occurs

• Analog voltmeters and ammeters
• Pressure gauges
• Analog thermometers
• Laboratory measurement devices with dial or pointer scales

These types of instruments are prone to reading errors if not viewed correctly.

How to Avoid Parallax Error

1. View the scale straight-on
   Always position your eyes directly in front of the pointer. The line of sight should be perpendicular to the scale.
2. Use instruments with mirror scales
   Many analog instruments have a mirror strip behind the pointer. When you align the pointer and its reflection, you are at the correct angle.
3. Digital Instruments
   Using digital measuring devices eliminates parallax error completely since there is no pointer or scale.
4. Practice correct observation
   Train users and students to develop the habit of checking their eye position while taking readings.
5. Design improvements
   Instruments should be built with small distances between the pointer and the scale to reduce the chance of error.

Importance of Avoiding Parallax Error

Avoiding parallax error is essential in:

• Electrical measurements, where small errors affect circuit performance.
• Laboratory experiments, where precision is needed.
• Calibration processes, where accuracy must match standards.
• Educational settings, where students are learning to take readings properly.

Small parallax errors may not seem big, but repeated mistakes can lead to major faults in calculations or system performance. In safety-related systems, even slight errors can be harmful.

Conclusion

Parallax error is a simple but common measurement mistake that occurs when the scale is not viewed from the correct angle. It can lead to inaccurate readings, especially in analog instruments. To avoid it, one should always view the scale head-on and use mirror scales if available. With careful observation and proper instrument design, parallax error can be completely avoided, ensuring more accurate and trustworthy measurements in electrical engineering and other fields.