A thermos flask is polished well to reduce loss of heat by

Options

A. conduction
B. convection
C. radiation
D. none of these

Answer

To solve the question about why a thermos flask is polished well to reduce the loss of heat, we can analyze the different modes of heat transfer: conduction, convection, and radiation.

### Step-by-Step Solution:

1. **Understanding Heat Transfer Modes**:
- Heat can be transferred in three main ways: conduction, convection, and radiation.
- Conduction occurs when heat is transferred through direct contact between molecules.
- Convection occurs in fluids (liquids and gases) where warmer, less dense areas of fluid rise and cooler, denser areas sink, creating a circulation pattern.
- Radiation is the transfer of heat in the form of electromagnetic waves, which can occur in a vacuum.

2. **Role of Polishing in a Thermos Flask**:
- A thermos flask is designed to minimize heat loss. Polishing the outer surface of the flask helps to reduce heat loss primarily through radiation.
- A shiny, polished surface reflects radiant heat back into the flask, preventing it from escaping into the environment.

3. **Impact of Polishing on Conduction and Convection**:
- While polishing does not significantly affect conduction and convection (since these processes depend more on the materials and the design of the flask), it is primarily effective against radiation.
- The inner surfaces of a thermos flask are often coated with reflective materials (like silver) to further minimize heat loss through radiation.

4. **Conclusion**:
- Therefore, the main reason for polishing a thermos flask is to reduce heat loss by radiation. This is crucial for maintaining the temperature of the contents inside the flask, whether hot or cold.

### Final Answer:
A thermos flask is polished well to reduce the loss of heat primarily by minimizing heat loss through radiation.