Question
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At 43.8 degree C, the resistance of a segment of gold wire is 130.1 ohm. When the wire is placed in a liquid bath, the resistance decreases to 96 ohm. What is the temperature of the bath? The temperature coefficient of resistivity for gold is 0.0034 ( degree C)-1 at 20 degree C. Answer in units of degree C A platinum resistance thermometer has a resistance of 200 when placed in an ice 0 degree C bath and 221.2 ohm when immersed in a crucible containing a melting substance. What is the melting point of the substance? The temperature coefficient of the platinum is 0.00392 ( degree C)-1. The resistor was calibrated at a temperature of 20 degree C.
Explanation / Answer
1)
Resistance = R(initial)[1+ alpha (T(final) - T(initial)]
96= 130.1 [1+ 0.0034(T(final) - 43.8]
T(final)= -33.89 C
2)
Resistance of metals reduces with temperature.
R(T) = R? [ 1 + ? T ]
221.2 = 200 [ 1 +0.00392 T ]
T ( melting point) = 26.91 C