In which instrument following are essential ?
(i) Internal vacuum
(ii) Use of electromagnets
(iii) Use of beam of electrons.

Answer

**Step-by-Step Solution:**

1. **Identify the requirements listed in the question:**
- Internal vacuum
- Use of electromagnets
- Use of a beam of electrons

2. **Determine the instrument that utilizes these requirements:**
- The instrument that requires an internal vacuum is typically an electron microscope. This is because the presence of air can scatter the electrons, which would interfere with the imaging process.

3. **Explain the role of each requirement in the instrument:**
- **Internal Vacuum:** The vacuum is essential to prevent electrons from colliding with air molecules, which would degrade the quality of the image.
- **Use of Electromagnets:** Electromagnets are used in electron microscopes to focus and direct the beam of electrons onto the specimen. They act as lenses that manipulate the path of the electrons.
- **Use of Beam of Electrons:** The electron beam is the primary source of illumination in an electron microscope. It allows for the visualization of the specimen at a much higher resolution than light microscopes.

4. **Conclude with the capabilities of the instrument:**
- An electron microscope can magnify objects up to 200,000 times, allowing scientists to observe structures at the cellular and molecular levels.

**Final Answer:**
The instrument that requires an internal vacuum, uses electromagnets, and employs a beam of electrons is the **Electron Microscope**.

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