До конца! Сколько вспышек убьют Мону Лизу? #физика

Exploring how many camera flashes it takes to fade the Mona Lisa using physics and the photoelectric effect.

Key Takeaways

Ultraviolet light from camera flashes damages ancient paintings by breaking down pigments.
The photoelectric effect explains how photons can destroy molecules in the paint.
A rough estimate shows about 100,000 flashes would be required to significantly fade the Mona Lisa.
Museum flash bans protect priceless artworks from cumulative light damage.
Physics principles can be applied to real-world problems like art preservation.

What the video covers

Photographing the Mona Lisa is allowed but using a flash is forbidden due to damage caused by ultraviolet light.
Ultraviolet light from flashes burns away ancient pigments, causing paintings to fade over time.
The video estimates the number of flashes required to significantly fade the Mona Lisa using physics calculations.
A single flash has about 100 joules of energy, and the energy of one photon is calculated using the photoelectric effect threshold.
Only ultraviolet photons cause damage by triggering the photoelectric effect, which knocks electrons out of molecules.
Assuming 10% of a flash's energy is ultraviolet, the number of damaging photons per flash is about 10^18.
The total number of atoms in the painting is roughly on the order of Avogadro's number, about 10^24.
Dividing the total atoms by photons per flash gives an estimate of 100,000 flashes needed to ruin the painting.
The conclusion is that 100,000 flashes would cause the Mona Lisa to fade to black and white.
The video explains the physics concepts in a simple, educational manner relevant for physics exam preparation.

Chapters

Why is flash photography banned in museums?

Flash photography is banned because ultraviolet light from flashes damages ancient pigments by triggering the photoelectric effect, which breaks down molecules and causes paintings to fade.

How many flashes would it take to ruin the Mona Lisa?

Based on physics calculations, it would take approximately 100,000 flashes to significantly fade the Mona Lisa's pigments and ruin the painting.

What physics concept explains the damage caused by flashes?

The photoelectric effect explains the damage, where ultraviolet photons knock electrons out of molecules in the paint, effectively destroying them and causing fading.

Full Transcript — Download SRT & Markdown

Speaker A

You can photograph the Mona Lisa, but it is strictly forbidden to use a flash. There is an important reason for this. Millions of tourists snap the painting every day, and flashes are banned in all museums because

Speaker A

ultraviolet light literally burns away ancient pigments, turning bright paintings faded. Is there any way to calculate how many times you need to photograph the Mona Lisa for it to fade?

Speaker A

Well, let's see, how should we handle this? For simplicity, let's just calculate it, shall we? We'll make an estimate. I'll take a wild guess and maybe I'll hit the mark. So, look, we have 100 joules—that's the energy of

Speaker A

a flash. The energy of one photon is hν. H-nu. To trigger the photoelectric effect, you need about 5 electron volts. We multiply 5 electron volts by the charge of one electron, 1.6 times 10 to the power of -19. That will be, in

Speaker A

joules, some eight microscopic joules. Next, we need to divide the flash energy by the energy of one photon. In this way, we will get the number of photons. We divide 100 joules by all that stuff. We get about 10 to the 19th

Speaker A

power of photons contained in one flash total, but only the photons capable of triggering the photoelectric effect do the burning. This phenomenon is in the physics state exam. The photoelectric effect is when a photon hits a surface and knocks out an electron. In doing so

Speaker A

, the molecule, in a sense, is essentially destroyed. It turns out we only need ultraviolet photons. A flash isn't just ultraviolet; it contains the whole visible spectrum to provide good lighting, but there is some fraction of ultraviolet in it. What fraction should

Speaker A

we assume, what do you think? 10%. Let's take 10%, the comments will correct us. So we need to take that 10%, which means taking 1/10th of it. We divide that by 10 and get 10 to the 18th power. And how many atoms are

Speaker A

there in the painting total? Let's assume all the ultraviolet light is absorbed. And how many are there?

Speaker A

Well, on the order of Avogadro's number. 6 times 10 to the 23rd. Let's round it to 10 to the 24th.

Speaker A

Close enough. What? 10 to the 19th, 10 to the 24th. Five orders of magnitude. Okay.

Speaker A

Wait. Right. 10 to the 24th divided by 10 to the 19th equals 100,000. That is my answer to your question.

Speaker A

100,000 photos. Take 100,000 flashes. And the painting will be ruined, just black and white.

Speaker A

Yeah.

Topics:Mona Lisaphotoelectric effectultraviolet lightcamera flashart preservationphysics calculationenergy of photonAvogadro's numbermuseum rulesphysics education

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