Physics · Series and parallel combinations of resistors, temperature dependence of resistance
Two resistance thermometers are made, one of the platinum wire and the other of
Two resistance thermometers are made, one of the platinum wire and the other of germanium wire. The resistance of both the thermometers are equal at room temperatures. Now the two resistance wires are connected to a battery. The two resistance wire are heated to \( 100^{\circ} \mathrm{C} \). The potential drop in the two resistance is measured. Which of the following statements is correct?
- A. The potential drop across the platinum wire is equal to the potential drop across the germanium wire
- B. The potential drop across platinum wire is greater than that across germanium
- C. The potential drop across the platinum wire is less than that across germanium
- D. The nature of the potential drop can be ascertained unless the magnitude of the current is known
Step-by-step solution
Platinum has a positive temperature coefficient (resistance increases with temperature), while germanium has a negative temperature coefficient (resistance decreases with temperature). At room temperature, their resistances are equal. When heated to 100°C, the resistance of platinum becomes greater than that of germanium. If they are connected in series (common assumption for such comparisons), the same current flows through both, so the potential drop (V=IR) is larger across the higher resistance, i.e., platinum.
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