Which of the following statements are true?

Options

A. Hole in the wall of a cavity radiator behaves like a black body
B. Hole in the wall of a cavity radiator does not act like a black body
C. When a body is kept in a surrounding of low temperature it does not absorb any energy from the surroundings
D. When a body is kept in surrounding of low temperature it simultaneously radiates heat to the surroundings and absorbs heat from the surroundings.

Explanation

To determine which statements are true regarding heat transfer, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement 1: The hole in the wall of a cavity radiator behaves like a black body.**
- A cavity radiator is designed to absorb all incoming radiation. When radiation enters through the small hole, it reflects multiple times within the cavity before either being absorbed or escaping. This behavior mimics that of a black body, which absorbs all incident radiation.
- **Conclusion:** This statement is **true**.

2. **Statement 2: (Not provided in the transcript, but let's assume it is false based on the context.)**
- Since the transcript indicates that the second option is incorrect, we conclude that this statement is **false**.

3. **Statement 3: When a body is kept in a surrounding of low temperature, it does not absorb any energy from the surrounding.**
- According to the principles of thermodynamics, any body at a temperature above absolute zero will absorb and emit radiation. A body in a cooler environment can still absorb energy, albeit less than it emits. Therefore, this statement is incorrect.
- **Conclusion:** This statement is **false**.

4. **Statement 4: When a body is kept in a surrounding of low temperature, it simultaneously radiates heat to the surrounding and absorbs heat.**
- This statement aligns with the laws of thermodynamics. A body in a cooler environment will indeed radiate heat away while also absorbing some heat from its surroundings. This process occurs continuously, depending on the temperature difference.
- **Conclusion:** This statement is **true**.

### Final Summary:
- **True Statements:** 1 and 4
- **False Statements:** 2 and 3