What is the first thing you should do before turning a microscope on?

• A. Turn the rheostat down
• B. Check the oil
• C. Clean the lenses
• D. Turn on the light

Answer: (A)

Set the illumination to its lowest setting with the rheostat before powering the microscope. This protects the lamp and your eyes from a sudden burst of bright light and gives you a safe starting point to increase brightness gradually as you focus and view the slide. Once the light is on, you can raise the intensity as needed to get a clear field of view.

The other actions aren’t the first thing to do: oil is for certain high-magnification oil-immersion work and isn’t something you set before turning on, cleaning lenses is important if there’s visible dirt but not a mandatory first step, and turning on the light should follow setting the rheostat to a low level rather than precede it.