Which pre-use safety step should be performed before powering the microscope on?

• A. Turn on the light
• B. Turn the rheostat down
• C. Increase brightness
• D. Check the stage alignment

Answer: (B)

Starting illumination with caution is the safety principle here. The rheostat is the dimmer that controls light intensity. Turning it down before powering the microscope on prevents a sudden blast of bright light and heat as the lamp starts up. This protects your eyes from glare and reduces stress on the lamp and optics while you’re preparing to observe. Once the power is on, you can gradually increase brightness to the level you need as you focus and view the specimen.

The other actions aren’t pre-use safety steps: turning on the light or increasing brightness should follow power-up, and checking stage alignment is something you do once you’re ready to observe and locate the specimen.