181A periscope commonly uses two plane mirrors or prisms mainly to let a person do what?
182A kaleidoscope creates colorful repeating patterns mainly through the use of what optical components?
183Thunder is generally heard a few seconds after lightning is seen mainly because what is true?
184What is the SI unit used to measure the strength of an electric current?
185The volt is the SI unit used to measure what electrical quantity?
186A short circuit occurs when electric current takes an unintended path of very low what?
187Electrical insulation around wires is mainly intended to prevent what safety hazard?
188An earthing or grounding wire in household wiring mainly provides a safe path for what?
189A fluorescent tube light produces visible light mainly using mercury vapor and what coating?
190A traditional incandescent light bulb produces light by heating a filament, commonly made of what metal, until it glows?
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