In the context of Doppler effect in light, the term red shift signifies

Options

A. Decrease in frequency
B. Increase in frequency
C. Decrease in intensity
D. Increase in intensity

Answer

To solve the question regarding the term "red shift" in the context of the Doppler effect in light, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Doppler Effect**:
- The Doppler effect refers to the change in frequency (and wavelength) of a wave in relation to an observer who is moving relative to the wave source. When the source of light moves away from the observer, the light appears to shift in wavelength.

**Hint**: Recall that the Doppler effect can occur with all types of waves, including sound and light.

2. **Identifying Red Shift**:
- In the context of light, "red shift" occurs when the source of light is moving away from the observer. This results in an increase in the wavelength of the light observed.

**Hint**: Remember that red light has the longest wavelength in the visible spectrum.

3. **Effect on Wavelength and Frequency**:
- As the wavelength increases (shifts towards red), the frequency of the light must decrease. This is because the speed of light (c) is constant, and the relationship between speed, wavelength (λ), and frequency (ν) is given by the equation:
\[ c = \lambda \cdot \nu \]
- If λ increases, then ν must decrease to keep the equation balanced.

**Hint**: Think about how frequency and wavelength are inversely related when the speed of light is constant.

4. **Conclusion**:
- Therefore, in the context of the Doppler effect, red shift signifies a decrease in frequency of the light observed as the source moves away from the observer.

**Final Answer**: Red shift signifies a decrease in frequency.