A Tungsten Wire Is $1.50 \mathrm {~m}$ Long and Has a Diameter Of

question 57

Short Answer

A tungsten wire is $1.50 \mathrm {~m}$ long and has a diameter of $1.00 \mathrm {~mm}$ . At $20 ^ { \circ } \mathrm { C }$ a current of $50 \mathrm {~mA}$ flows through this wire. The temperature coefficient of resistivity for this tungsten is $4.5 \times$ $10 ^ { - 3 } / \mathrm { C } ^ { \circ }$ , and its resistivity at $20 ^ { \circ } \mathrm { C }$ is $5.6 \times 10 ^ { - 8 } \Omega \cdot \mathrm { m }$ .
(a) What is the potential difference across the ends of this wire at $20 ^ { \circ } \mathrm { C }$ ?
(b) If the wire temperature increases by $100 \mathrm { C } ^ { \circ }$ , what potential difference across its ends is now required to produce a current of $50 \mathrm {~mA}$ ?