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Which instrument has a necessarily the "square law" type scale?

  • Hotwire instruments has a necessarily the "square law" type scale.
  • A hot-wire instrument is a type of instrument used for measuring the flow of gases or fluids.
  • It works based on the principle that the rate of flow of a gas is directly proportional to the cooling effect on a heated wire placed in the flow path of the gas.
  • The amount of cooling produced by the gas flow is measured by the change in resistance of the wire.
  • The scale of a hot-wire instrument is typically a square law scale.
  • This means that the deflection of the instrument is proportional to the square of the current flowing through the instrument.
  • This is because the resistance of the wire is directly proportional to the temperature, which is in turn proportional to the square of the current.
  • The square law scale is necessary for hot-wire instruments because the cooling effect on the wire is not directly proportional to the flow rate of the gas.
  • Instead, it is proportional to the square of the flow rate. Therefore, to produce a linear scale for flow measurement, the instrument must have a square law scale.