Study Guides/Physics/Accuracy vs Precision
Study Guide · Physics

Distinguish Between Accuracy and Precision

In everyday language, 'accuracy' and 'precision' mean the same thing. But in science and Physics (Class 11 Units and Measurements), they have very different and specific meanings when taking measurements.

Question (Click to Flip)

Distinguish between accuracy and precision.

Answer

Accuracy is how close a measurement is to the true or accepted value. Precision is how close repeated measurements are to each other, showing the consistency or exactness of the instrument.

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Key Facts

Accuracy: Closeness to the True Value.

Precision: Closeness of multiple measurements to each other (consistency).

High Precision doesn't mean High Accuracy: You can consistently measure the wrong value!

Precision is linked to the resolution/least count of the measuring tool.

1. Accuracy

  • Definition: Accuracy refers to how close a measured value is to the actual (true) value.
  • Meaning: If a textbook weighs exactly 2.0 kg, and your weighing scale says 2.01 kg, your scale is highly accurate. If it says 3.5 kg, it is inaccurate.
  • Depends on: Calibration of the instrument. Systematic errors reduce accuracy.

2. Precision

  • Definition: Precision refers to how close multiple measurements are to each other, regardless of whether they are close to the true value.
  • Meaning: It describes the exactness or resolution of the instrument. A scale that measures up to 3 decimal places (2.015 kg) is more precise than one measuring 1 decimal place (2.0 kg).
  • Depends on: The least count of the instrument. Random errors reduce precision.

The Dartboard Analogy

Imagine throwing darts at a dartboard (the bullseye is the 'true value'):

  1. Accurate & Precise: All darts hit right in the bullseye.
  2. Precise but NOT Accurate: All darts hit closely together, but far away from the bullseye (e.g., in the top right corner).
  3. Accurate but NOT Precise: Darts are scattered widely around the board, but their average centre is the bullseye.
  4. Neither: Darts are scattered widely and far from the bullseye.

Questions and Answers

Distinguish between accuracy and precision.+

Accuracy is how close a measurement is to the true or accepted value. Precision is how close repeated measurements are to each other, showing the consistency or exactness of the instrument.

If all arrows hit the edge of the target tightly grouped together, is it accurate or precise?+

It is precise (because they are grouped tightly together), but it is NOT accurate (because they missed the bullseye/true value).

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