Under what ideal condition the efficiency of a Carnot engine be 100%.

Explanation

To determine the ideal condition under which the efficiency of a Carnot engine can be 100%, we need to understand the relationship between the temperatures of the heat source and the heat sink.

### Step-by-Step Solution:

1. **Understanding the Carnot Engine**:
- A Carnot engine operates between two thermal reservoirs: a hot reservoir (source) at temperature \( T_1 \) and a cold reservoir (sink) at temperature \( T_2 \).
- The engine absorbs heat \( Q_1 \) from the hot reservoir and rejects heat \( Q_2 \) to the cold reservoir while performing work \( W \).

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