What Is the photoelectric Effect?

The photoelectric effect *occurs when light (or similar radiation such as X-rays) falls on a material such as a metal plate and causes it to emit electrons. The discovery of the photoelectric effect led to important new theories about matter (and to a Nobel Prize for Albert Einstein). *Photoelectric cells, *or *photocells, are used in burglar-alarm light detectors and garage-door openers (both employ a beam of light that is broken when something moves across it), and also to play soundtracks on movie film (where a light beam shines through the soundtrack encoded on the film and is "read" by the photocells).

Examples of photoelectric in a Sentence

Recent Examples on the Web One is whether to get a dual-sensing detector, with both a photoelectric eye to quickly detect smoke and an ionization sensor, often called a heat detector, to quickly detect flames. — Washington Post, 27 Sep. 2021 For the best protection, photoelectric smoke alarms are the new standard. — Shirley Macfarland, cleveland, 5 Nov. 2021 Examples include First Alert’s hard-wired smoke alarm with photoelectric sensor ($35.74 on Amazon) and Kidde’s 10-year worry-free hard-wired smoke detector with intelligent wire-free voice ($49.97 at Home Depot). — Washington Post, 27 Sep. 2021 Increase safety by using a dual-sensor smoke alarm, which detects smoldering and flaming fires by using both a photoelectric and an ionization sensor in one unit. — Nicole Bradley, Better Homes & Gardens, 2 June 2020 Its photoelectric sensor alerts you when the unit needs cleaning of dust and buildup, which can trigger the alarm. — Nicole Bradley, Better Homes & Gardens, 2 June 2020 Employees relied on the operation of a photoelectric switch to de-energize street lights before installing the camera. — Madeline Mitchell, Cincinnati.com, 11 Dec. 2019 In other business, council authorized Fire Chief Patrick Sweeney to apply to the Federal Emergency Management Agency for a $25,000 Fire Prevention and Safety Grant to purchase optical or photoelectric smoke detectors. — Thomas Jewell, cleveland.com, 28 Feb. 2018 Classical physics held that light was a wave, but that theory couldn’t explain how and why metals emit electrons when illuminated—a phenomenon called the photoelectric effect. — Michael Greshko, National Geographic, 10 Feb. 2016 See More

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'photoelectric.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.