GPL - Measurement - Terminologies and Methods

 

MEASUREMENT OF PHYSICAL QUANTITIES

Ways to measure:

  • Direct measurement: read directly from the device
  • Indirect measurement: value is determined by formula or relation among it and other quantities.

Measuring units in SI: 

Include: length, mass, time, temperature, electric current, amount of substance, luminous intensity (độ sáng)
Subsidiary quantities and unit: plane angle and solid angle
Derived quantities and unit: quantities which are derived since their dimensions are derived from base quantities by multiplication and division.
Prefix: tiền tố đặt trước đơn vị nhằm xác định độ nhỏ hay độ to của đơn vị cơ bản
Dimensionless quantities: đại lượng không có đơn vị khi ta thực hiện phép chia của hai đại lượng có một đơn vị (hằng số hoặc tỉ lệ)

Errors occuring during the measurement:

Fact: no measurement is free of uncertainties.
Error of the measured quantity $x$ is denoted by $\triangle x$: $\triangle x = x_{true} - x$
Accuracy: tính đúng của sự đo đạc
Precision: sự lặp lại nhiều lần đo đạc
Uncertainty: interval around the true value
Bias: the difference between the avarage value and the accepted true. $\overline{x}$ and $x$
Blunders: sai sót thực tế (đo sai thang)

Types of errors:

  1. Coarse error: lỗi chủ quan
  2. Systematic error: lỗi đo đạc từ các đại lượng
  3. Random error: như tên của nó :) 

Methods of data processing:

Single measurement
Multiple measurement: repeat measuring of a quantity and then collect the data

Rules to present the final result:

  1. If the result is very small or very big, present it in scientific notation.
  2. Keep three digits after the decimal point
  3. The absolute error must be presented in the same notation as measured quantity.
  4. The absolute error must be rounded to the first significant figure
  5. The result must be in the form $(x + \triangle x)$ [units] (if the absolute value is less than the result, left the zeros behind the value)

Graphical representation of data:

  1. Decide which quantity to be plotted
  2. Use a Cartesian coordinate system (hệ trục tọa độ Đề cát)
  3. Decide which origin to appear on the graph
  4. Choose a scale
  5. Write a label in the margin next to each axis which indicates the quantity
  6. Write a label in the margin at the top of the graph that indicates the nature of the graph
  7. Plot points
  8. Draw a smooth curve that comes close to all of the points