A wire is heated gradually as temperature rises, at first it appears :

Options

A. red
B. green
C. yellow
D. white

Answer

To solve the question about the color appearance of a wire as it is heated gradually, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Problem**:
The question asks what color a wire appears when it is gradually heated. We need to consider the relationship between temperature and the color emitted by the wire.

2. **Applying Wien's Displacement Law**:
We use Wien's Displacement Law, which states that the wavelength (λ) of the radiation emitted by a black body is inversely proportional to its absolute temperature (T). Mathematically, this can be expressed as:
\[ λ \propto \frac{1}{T} \]
This means that as the temperature increases, the wavelength of the emitted radiation decreases.

3. **Identifying the Color Corresponding to Wavelengths**:
Different colors correspond to different wavelengths:
- Red light has the longest wavelength.
- As the temperature increases, the emitted radiation shifts from longer wavelengths (red) to shorter wavelengths (green, yellow, white, etc.).

4. **Determining the Initial Color**:
When the wire is heated gradually, the first color that will be emitted corresponds to the longest wavelength, which is red. As the temperature continues to rise, the color will shift to green, yellow, and eventually white as the temperature increases further.

5. **Conclusion**:
Therefore, when the wire is heated gradually, it first appears red.

### Final Answer:
The wire first appears **red** when heated gradually.