Final Answer:
The provided options for the time constant (τ) in Example 20.3 are not consistent with the given values. Therefore, I cannot determine the correct answer based on the information provided.
Step-by-step explanation:
The question refers to Example 20.3, but the options provided for the time constant (τ) do not match the format used in the original example. In the absence of the specific details from Example 20.3 and with inconsistent options, it is not possible to provide a meaningful calculation or choose the correct answer.
If you can provide the relevant details or clarify the discrepancy in the options, I would be happy to assist in solving the problem. Please ensure that the values and units are consistent with the context of the original example.