The temperature coefficient of resistance of tungsten is 4.5 × 10^(-3)...
To determine the value of resistance \( R \) for the germanium wire such that the total resistance of the series combination remains constant with temperature, we can use the temperature coefficients of resistance.
Understanding Temperature Coefficients
- The temperature coefficient of resistance for tungsten ( \( \alpha_T \) ) is \( 4.5 \times 10^{-3} \, °C^{-1} \).
- The temperature coefficient of resistance for germanium ( \( \alpha_G \) ) is \( -5 \times 10^{-2} \, °C^{-1} \).
Resistance Change with Temperature
- The resistance of a conductor changes with temperature according to the formula:
\[ R(T) = R_0 (1 + \alpha (T - T_0)) \]
where \( R_0 \) is the initial resistance, \( \alpha \) is the temperature coefficient, and \( T \) is the temperature.
Finding the Condition for Constant Resistance
- For the tungsten wire, the change in resistance with temperature is:
\[ R_T(T) = 100 \, (1 + 4.5 \times 10^{-3} (T - T_0)) \]
- For the germanium wire, the change in resistance is:
\[ R_G(T) = R \, (1 - 5 \times 10^{-2} (T - T_0)) \]
- The total resistance \( R_{total} \) is:
\[ R_{total}(T) = R_T(T) + R_G(T) \]
- For the combination to remain constant, the change in resistance due to tungsten must equal the opposite change due to germanium:
\[ 100 \cdot 4.5 \times 10^{-3} = R \cdot 5 \times 10^{-2} \]
Calculating R
- Rearranging gives:
\[ R = \frac{100 \cdot 4.5 \times 10^{-3}}{5 \times 10^{-2}} \]
\[ R = \frac{0.45}{0.05} = 9 \, \Omega \]
Conclusion
- The value of resistance \( R \) for the germanium wire to ensure that the total resistance does not change with temperature is \( 9 \, \Omega \).
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