Mathematical and Physical Journal
for High Schools
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# Problem P. 4092. (September 2008)

P. 4092. A laser emits light impulses of wavelength 580 nm and of energy 20 J, which last for 0.5 ms. This light is aimed perpendicularly at a sheet made of caesium, and is focused to a circle of diameter 12 mm. 90% of the light is absorbed and 10% is reflected.

a) How many photons hit the metal sheet during one impulse?

b) Find the pressure of light.

c) Find the maximum of the speed of the electrons which are ejected by the caesium sheet.

(5 pont)

Deadline expired on October 13, 2008.

### Statistics:

 83 students sent a solution. 5 points: Balassa Péter, Bali-Papp Donát, Balogh Gábor, Börcsök Bence, Csengeri Béla, Csopor Dávid, Deák Zsolt, Emroz Khan, Englert Dávid, Filep Gábor, Filep Tibor, Fonai Dániel, Földes Imre, Hartstein Máté, Hoksza Zsolt, Illés Dorottya, Iván Dávid, Jakab Dávid, Jéhn Zoltán, Kovács 235 Gábor, Kovács Benjámin, Krämer Zsolt, Kunsági-Máté Éva, Lászlóffy András, Lénárt Tamás, Lovas Lia Izabella, Maknics András, Márkus Bence Gábor, Najbauer Eszter Éva, Pálovics Péter, Patartics Bálint, Pázmán Koppány, Rácz Viktor, Sós Attila Róbert, Szabó 928 Attila, Szédelyi Roland, Szük Dániel, Török 999 Csaba, Vécsi Áron, Zsolczai Viktor. 4 points: 20 students. 3 points: 14 students. 2 points: 5 students. 1 point: 2 students. 0 point: 1 student. Unfair, not evaluated: 1 solution.

Problems in Physics of KöMaL, September 2008