Physics mysteries

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What color is the atom (Source: © navintar /

Can be anything colder than absolute zero?

Jaroslav Kores, Ph.D.

The value of absolute zero is -273.15 ° C. Could an object be cooled even more, for example to -300 ° C? If not, why?
The very definition of absolute zero says that 0 K (i.e. -273.15 ° C) cannot be achieved. It is one example of the limitations that nature gives us. Why this is so (that is, why nature limits us in this way) is more of a philosophical question but it can be shown in several cases that reaching absolute zero would be at least strange. Even stranger would be negative temperatures (in Kelvin). We know that bodies shrink during cooling. It is best seen on gases. If we cool a gas, its volume will decrease. If we reached 0 K, its volume would be zero. That is certainly not possible. The gas pressure would behave similarly - if we cool a gas, the gas pressure decreases. And at 0 K, the pressure would be zero. That is also impossible ...
What color is the atom (Source: © weyo /

Why is my food heated in the microwave and not a plate?

Jaroslav Kores, Ph.D.

When I put a cold plate of cold soup in the microwave, I take out a cold plate of hot soup in a minute. How does the microwave know what to heat?
The microwave oven is an example of an invention that was created not on the basis of a theoretical design, but happened by chance. While working on military radar components, Percy Spencer discovered that a chocolate bar in his pocket had melted. He researched further and the result was a microwave. Warm bodies differ from cold ones in that the molecules move faster in them. The faster the molecules move, the higher the temperature of the body. We can move molecules in different ways (e.g. collisions of surrounding molecules - so-called conduction) but we always need some form of energy for that. When a molecule receives energy, it starts moving. Microwave radiation has energy just like any other radiation ...
What color is the atom (Source: © FullRix /

What color is the atom?

Jaroslav Kores, Ph.D.

All things around us have some colour or they are for instance, transparent. But what colour are the atoms from which it is all made? First of all, we will distinguish what the possibilities are for a thing to have colour.
The first possibility is that the thing (the Sun, a bulb, fire) emits light. In this case, the colour of light is determined by the material of the body and its temperature (so the Sun is yellow just because it consists of hydrogen and has a temperature of about 6,000 ° C). Iron is orange during the casting just because it has a certain temperature and because it consists of iron. The second way bodies can get their colour is reflection and light absorption. The body that reflects light is for example, red because it reflects red but absorbs other colours. So if we shine blue or green on a red body, it will be black. Black bodies are those that absorb all colours (that's why black heats up the most) and white bodies are those that reflect all colours ...
Is the electricity returning to the power plant (Source: © Negro Elkha /

Is the electricity returning to the power plant?

Jaroslav Kores, Ph.D.

If we build a simple electrical circuit, electric current flows from the battery into the bulb, turns it on, and then flows to the other pole of the battery. How is it in reality? Is the electricity from my lightbulb coming back through wires to the power plant?
I will try to explain the question with an analogy of the postal services. We use electricity to fulfil its work and the post office to send packages. In the case of the electricity, charged particles (especially electrons, but also ions) do the work. At the post office, the postman does the work (in the case of Amazon, a drone is planned). In the case of the post office, it is clear that it is best for us that the postman would return to the post office after delivering the letters so that he can continue the next day. It's the same with electricity - we also need the electrons to come back so that they can do the work in the electrical circuit again ...
What would happen to a man inside a particle accelerator (Source: © francescodemarco /

What would happen to a man inside a particle accelerator?

Jaroslav Kores, Ph.D.

In the particle accelerator, particles collide at a speed close to the speed of light, creating a number of exotic particles. What would happen if a person took the place of a target at the LHC? Would he gain superpowers as in movie?
It could be expected that outside of sci-fi movies, we will not know how a human would end up if they were exposed to the current of really accelerated particles in the accelerator, but in the 1970s, something similar happened in Russia. Anatoly Bgorsky inserted his head into a proton accelerator because of a failure in the security device and beams of accelerated protons flew through his head. He survived the accident, but if we do not include migraines, epilepsy and hearing loss among the superpowers, he was very lucky. Energy of the proton beam was much higher than the lethal dose for a human, but because the bundle of protons was very condensed and not dispersed, only a narrow part of the brain was burned. It is something like when a very thin hot wire would go through a tissue ...
How wide is the rainbow (Source: ©nighttman /

How wide is the rainbow?

Jaroslav Kores, Ph.D.

In addition to visible light, there are other components in the electromagnetic spectrum - ultraviolet and infrared, radio and X-rays. When a rainbow appears in the sky after the rain, which of those invisible components of the electromagnetic spectrum are "visible" on it?
Light colour is made by its frequency and as you write correctly, light is a type of electromagnetic wave and is specific "only" by that it is about the frequencies we see. The frequency of the electromagnetic waves can be arbitrary and so our perception is limited to a narrow part of the spectrum (in frequencies 1014 Hz). We do not perceive the remaining frequencies with our eyes, but we know that they exist (e.g. the mentioned IR and UV radiation). Because it's still an electromagnetic wave, the invisible frequencies conduct even to us just as light. Therefore, the so-called dispersion, will also occur with IR or UV. This is a phenomenon in which light decomposes into different colours (more precisely frequencies) and which we can observe at the formation of the rainbow ...
Text in a car’s rearview mirror (Source: © ElenaKyrylova /

Text in a car’s rearview mirror

Jaroslav Kores, Ph.D.

Why is the ambulance sign on an ambulance reversed when looking in the mirror and it is clear that the sides of the displayed object do not change — what is to the right in front of the mirror is to the right behind the mirror.
A convex mirror is used in a car’s rearview mirror — this is the reason it always creates a reduced and inverted image. But the image that is created is reversed. If you want to shake your right hand with your image in the mirror, you will see for yourself. From our point of view, the hand is on the right, but in reality one would shake your hand from the left. If you take the Ambulance sign in front of the mirror, you will see that the letter A is at the end (read from left to right) and the letter E at the beginning. In order for drivers to quickly see who is following them when looking in the rear-view mirror, the inscription on the vehicles of the rescue service or fire brigade is mirror-inverted.
Hypothetical rescue in a falling elevator (Source: © zphoto83 /

Hypothetical rescue in a falling elevator

Jaroslav Kores, Ph.D.

Can I save myself in a falling elevator by jumping just before impact?
I hope that no one will have to experience this situation because it will not be possible to jump in a falling elevator — I will explain the situation where we do not take into account the air resistance. If an elevator falls, the elevator will move with the acceleration of gravity g (we won’t count air resistance). When the elevator stops, the gravity of the Earth causes our body to fall down by accelerating with gravity, but the elevator floor prevents us from doing so. We feel solid ground under our feet. When we relax the muscles in our legs, our body will go down due to gravity and our legs will still remain on the floor. The moment the elevator breaks, it starts to fall with the same acceleration that we fall with ...
Lift forces on an aerobatic aircraft (Source: © qfiatoo /

Lift forces on an aerobatic aircraft

Jaroslav Kores, Ph.D.

How is it possible for an airplane to fly horizontally during aerobatics, even when it is upside down? The lift on the wings should pull him down and not up…
It is true that the plane takes off due to the geometry of the wings. The upper part is more bulging than the lower part and therefore the air flows at a higher speed around the upper part of the wing than the lower part. And it follows from Bernoulli’s equation that the higher the velocity of the fluid, the lower the pressure at a given location. However, if that were the case, the plane could only climb. We regulate the flow speed by controlling the propeller — the faster the plane flies, the faster the flow. So it would be possible to regulate the height of the aircraft by regulating its speed. But it’s not perfect. Therefore, aircrafts have rudders (at the rear of the aircraft). Turning the elevator changes the direction of the aircraft relative to the surroundings ...
Real plasma in flame (Source: © Aliaksandr Marko /

Real plasma in flame

Jaroslav Kores, Ph.D.

Is plasma formed during the burning of a flame? And if so, can the flame react to an electromagnetic field?
Plasma refers to a gas consisting of charged particles. Due to the high temperature of the flame, a neutral gas molecule (e.g., O2) can rupture into a free electron and a positive O2 ion and a candle flame can contain plasma. Indeed, such plasma is very sparse — there are fewer charged particles in it than the recommended molecules. The process that I have described as the rupture of molecules is called ionization. Ionization can be achieved in other ways (e.g. by candle flame, high temperature, or electromagnetic radiation) and we encounter it, for example, with lightning (see the question about lightning), fluorescent lamps or arc welding. Because plasma consists of charged particles, it reacts to both magnetic and electric ...
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