Stars A and B appear to be blue and red in colour, respectively. Then one can infer that

Options

A. star A is hotter than B
B. star B is hotter than A
C. the colour has no relevance to temperature of the star
D. they may have equal temperature

Answer

To solve the question regarding the colors of stars A and B, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Colors of the Stars**:
- Star A appears blue.
- Star B appears red.

2. **Understand the Relationship Between Color and Temperature**:
- The color of a star is related to its temperature. Blue stars are typically hotter than red stars.

3. **Relate Color to Wavelength**:
- The wavelength of light emitted by an object is inversely related to its temperature. This means that shorter wavelengths correspond to higher temperatures.
- Blue light has a shorter wavelength compared to red light.

4. **Apply Wien's Displacement Law**:
- According to Wien's Displacement Law, the product of the wavelength (λ) and the absolute temperature (T) of a black body is a constant (b).
- Mathematically, this is expressed as:
\[ \lambda \cdot T = b \]
- From this relationship, we can infer that:
\[ T \propto \frac{1}{\lambda} \]
- This means that as the wavelength decreases (becomes shorter), the temperature increases.

5. **Compare the Wavelengths of Stars A and B**:
- Since Star A is blue, it has a shorter wavelength (λ_A) than Star B, which is red (λ_B).
- Therefore, we can write:
\[ \lambda_A < \lambda_B \]

6. **Infer the Temperatures of the Stars**:
- Since the temperature is inversely proportional to the wavelength, we can conclude:
\[ T_A > T_B \]
- This indicates that Star A is hotter than Star B.

7. **Final Conclusion**:
- Based on the analysis, we can infer that Star A is hotter than Star B.

### Final Answer:
Star A is hotter than Star B.