Using Alpha Radiation in Smoke Alarms - GCSE Physics | kayscience.com

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A radioactive isotope of Americium-231 is used in smoke alarms because they emit alpha particles. The alpha particles ionise the air molecules between the charged plates. A current can now flow between the charged plates. A current detector measures the current, and if it’s high enough, the alarm doesn’t sound.
When smoke fills the smoke detector, it fills the gap between the charged plates.
This slows the ions between the charged plates, which reduces the flow of current in the circuit. The current detector detects a lower current, which causes the alarm to sound. When the smoke is cleared from between the charged plates, the ions move faster between the charged plates, and the current increases, which causes the smoke alarm to turn off.
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watching this before my physics final in about 2 weeks, thank you so much I truly grasped well the topic now, thanks a lot

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Great video. I liked the AFL and the repetition for emphasis. 👍

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Thank you for this video. Thank you for this video.

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[@JohnPrineas]

I finally understand, thanks for the help

[@daljinderdulai6770]

Do we need to know this for the edexcel gcse physics exam?

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[@alvin65415]

You say it ionises the air molecules, but why doesn't the alpha radiation ionise the smoke molecules? Also, where in the diagram is the current threshold set, how does the system know there is a drop in current?

[@Wafxersyy]

The smoke acts as a "resistor" and resistance is inversely proportional to current. So if the resistance increases, current decreases

[@zaydhassan1069]

Thanks so much!
Helped loads

[@kevinthiele1163]

is it americium 231 or 241?? u said both

[@golamarin8219]

241

[@ahmadbloodo]

Why does ionisation cause current

[@Lava-cj1fm]

positive and negative attract