Which of the following is/are not always necessary to observe a shadow?

Options

A. Sun
B. Screen
C. Source of light
D. Opaque object

Answer

To solve the question "Which of the following is/are not always necessary to observe a shadow?", we will follow these steps:

### Step 1: Understand the concept of a shadow
A shadow is formed when an opaque object blocks the path of light from a light source. To observe a shadow, we need three main components: a light source, an opaque object, and a surface (screen) where the shadow can be cast.

### Step 2: Identify the components necessary for a shadow
1. **Light Source**: This can be natural (like the sun) or artificial (like a bulb).
2. **Opaque Object**: This is the object that blocks the light.
3. **Surface (Screen)**: This is where the shadow is formed.

### Step 3: Analyze the options provided
The question asks which of the following is not always necessary to observe a shadow. The options likely include:
- Sun (natural light source)
- Source of light (can be any light source)
- Opaque object
- Screen (surface for the shadow)

### Step 4: Determine which option is not always necessary
- **Sun**: While the sun is a natural light source, it is not the only light source. Any light source can create a shadow, so the sun is not always necessary.
- **Source of Light**: A light source is always necessary to create a shadow.
- **Opaque Object**: An opaque object is essential to block the light and create a shadow.
- **Screen**: A screen is necessary to observe the shadow, as the shadow needs a surface to be visible.

### Conclusion
The correct answer is that the **sun** is not always necessary to observe a shadow, as any light source can replace it.

### Final Answer
The sun is not always necessary to observe a shadow.

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