When focusing a specimen under a light microscope, you should always start with the _____________ objective.

• A. low-power
• B. high-power
• C. oil immersion
• D. scanning electron

Answer: (A)

Verified step by step guidance

1. Understand the purpose of different microscope objectives: The scanning objective (usually 4x) is used for initial scanning, low-power objective (usually 10x) provides a broader view with more detail, high-power objective (usually 40x) offers greater magnification, and oil immersion (usually 100x) is for the highest magnification with oil to improve resolution.
2. Recognize that when focusing a specimen, it is best to start with the objective that provides the widest field of view and the least magnification to easily locate the specimen on the slide.
3. Identify that the scanning objective (4x) is often used first to find the specimen, but the question asks specifically about the objective to start focusing with, which is typically the low-power objective (10x) because it balances magnification and ease of focusing.
4. Recall that starting with the high-power or oil immersion objectives first is not recommended because they have a narrow field of view and require precise focusing, which is difficult without first locating the specimen at lower magnification.
5. Conclude that the correct objective to start focusing with under a light microscope is the low-power objective.