What are two essential features of Carnot’s ideal heat engine ?

Explanation

To answer the question about the two essential features of Carnot's ideal heat engine, we can break it down into the following steps:

### Step-by-Step Solution

1. **Understanding the Carnot Engine**: The Carnot engine is a theoretical construct that represents the most efficient heat engine possible. It operates between two thermal reservoirs: a hot reservoir (source) at temperature \( T_1 \) and a cold reservoir (sink) at temperature \( T_2 \).

2. **Feature 1 - Infinite Heat Capacity**: One of the essential features of the Carnot engine is that both the hot and cold reservoirs have infinite heat capacity. This means that the temperature of the reservoirs does not change, regardless of the amount of heat transferred to or from them. Thus, the heat source can provide heat \( Q_1 \) without its temperature decreasing, and the heat sink can absorb heat \( Q_2 \) without its temperature increasing.

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