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NCERT Class XII Chapter
Current Electricity
Questions With Solutions

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Question : 8
Total: 24
A heating element using nichrome connected to a 230 V supply draws an initial current of 3.2 A which settles after a few seconds to a steady value of 2.8 A. What is the steady temperature of the heating element if the room temperature is 27.0 °C ? Temperature coefficient of resistance of nichrome averaged over the temperature range involved is 1.70 × 10–4°C–1.
Solution:  
At room temperature 27 °C, the resistance of the heating element.
R27° =
230
3.2
 = 71.875 Ω
At the steady temperature t °C , the resistance.
Rt =
230
2.8
 = 82.143 Ω
Now , R2 = R1 [1 + α (t2−t1)]
or 82.143 = 71.875 [1 + 1.7 × 10–4 (t – 27)]
or 0.0840 × 104 = t – 27 or 840 = t – 27 or t = 867 °C.
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