Question
Download Solution PDFThe principle of operation of hot-wire instruments is:
This question was previously asked in
SSC JE EE Previous Paper 10 (Held on: 10 Dec 2020)
Answer (Detailed Solution Below)
Option 2 : thermal effect
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Download Solution PDF- The instruments which use the heating or thermal effect of the current for knowing their magnitude such type of instrument is known as the hot wire instrument.
- The hot wire instrument is used for both the AC and DC current.
- Hotwire instrument works on the principle of the thermal effect, that the length of the wire increases because of the heating effect of the current flow through it.
- When the current is passed through the fine platinum-iridium wire it gets heated up and expands.
- The sag of the wire is magnified, and the expansion is taken up by the spring.
- This expansion causes the pointer to deflect, indicating the value of the current.
- This expansion is directly proportional to the heating effect of the current and hence directly proportional to the square of the RMS value of the current.
- Therefore, the meter may be calibrated to read the rms value of the current.
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