7. A 34.5 m length of copper wire has a radius of 0.25 mm. If a potential difference of 9.00 V I applied to the wire when the temperature is 20" C. (a) what is the current in the wire? If the temperature is raised to 30 C, while the 9.00 V potential difference is maintained, (b) what is the resulting current in the wire? (Resistivity of copper is 1.7 x 10 0m, temperature coefficient of resistivity for copper is 3.9 x 103 .C.1] 8. A platinum resistance thermometer has a resistance of 200.0 Q when placed in an ice bath at -5.0 C. The resistance increases to 253.8 Q when the thermometer is immersed in a crucible of melted potassium. What is the melting point of potassium? (Resistivity of platinum is 11.0 x 10# Qm, temperature coefficient of resistivity for platinum is 3.92 x 103 "C.1)