A precision copper coil is used as the sensing element of an industrial temperature probe
PHYSICS · Multi-part · CBSE · Physics · Current Electricity · Current Electricity
Problem
A precision copper coil is used as the sensing element of an industrial temperature probe. When the probe is first inserted into a hot fluid, the coil is at 25 °C and a digital ammeter reads an initial current of 145 mA supplied by an ideal 5.0 V dc source. After thermal equilibrium is reached, the current has dropped to 128 mA. The temperature coefficient of resistivity for copper is α=0.0039°C−1. Assume the geometry of the coil does not change with temperature and that the source voltage remains exactly 5.0 V.
(a) Determine the resistance of the coil at 25 °C.
(b) Using the final current reading, determine the resistance of the coil after equilibrium is reached.
(c) Estimate the final temperature of the coil.
(d) Compute the percentage change in the power dissipated by the coil between 25 °C and the final temperature. Briefly explain why this percentage differs from the percentage change in current.