Analogue Apparatus & Interpolation (OCR A Level Physics)

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Analogue Apparatus & Interpolation

Analogue Apparatus

  • The type of analogue apparatus needed depends on the measurements to be made:

Analogue Apparatus Table

Analogue Apparatus Table, downloadable AS & A Level Physics revision notes

  • A large disadvantage of analogue instruments is parallax error
  •  This occurs when a scale reading is not read directly from the needle, but at an angle, therefore, seeming like a slight difference in reading
    • This can be fixed by a mirror behind the needle. When the needle and its mirror image are aligned, then the reading is correct

  • Parallax error is minimised by reading the value on a scale only when the line of sight is perpendicular to the scale readings (ie. at eye level)
  • Examples of where parallax error is common are:
    • Determining the volume of liquid
    • Making sure two objects are aligned
    • Reading the temperature from a thermometer

Parallax Error, downloadable AS & A Level Physics revision notes

Reading the value of the needle head-on (left image) looks different to reading it from the right (right image). This is parallax error 

Interpolation

  • Sometimes a pointer on an analogue meter can fall between two scale markings
    • In which case, interpolation between the scale markings is needed

  • Interpolation is the processes of estimating unknown values that fall between known values
    • For example, if a straight line passes through two points of known value, the point midway between them can be estimated

  • This is why calibration is very important
  • For example, a vernier caliper includes the main scale with certain scale markings
    • To then read between these markings, a vernier scale is used for accurate interpolation between the smallest divisions on the main scale
    • This means a reading can be obtained to a greater number of decimal places

Interpolation Between Scale Markings, downloadable AS & A Level Physics revision notes

The length of the wire falls between two scale markings

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Ashika

Author: Ashika

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Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.