A photovoltaic cell is a thin wafer of silicon modified to function as a semiconductor photodiode. When a photon hits its surface, it transfers its energy to one of the electrons, which is released from its electron shell. When enough electrons accumulate, a voltage is generated at the output of the photovoltaic cell ...

Gravity is a property of all material bodies and cannot be directly “produced”. Since the magnitude of the gravitational force depends on the mass and distance of the bodies acting on each other, we can make a smaller model of the Earth with the same gravitational effects on its surface ...

It certainly can, and in my opinion, it happens to a very limited extent. If we want anything to leave the Earth’s gravitational field, we have to give it the so-called 2nd escape velocity (or Ve). Everything we throw/fly slower will come back or will orbit the Earth in an ellipse. The value of this speed is (at the Earth’s surface) 11.2 km/s ...

The fact that the Moon orbits the Earth, does not fall on it and does not fly away, and in fact, the fact that it has become our companion, is due to a suitable combination of the speed of the Moon and its distance. According to Newton’s first law, bodies on which no force acts move in uniform rectilinear motion. If a force acts on a body, the body will move with acceleration ...

Small wind turbines can reach 30 to 60 revolutions per minute, but larger ones spin more slowly at a rate of perhaps only ten revolutions per minute. What may look like slow motion from a distance is actually quite fast when you focus on the tips of the propeller blades ...

A natural reactor really existed. It was “operated” in the Oklo locality in the West African state of Gabon. The uranium ore deposits there at that time contained around three percent of the isotope ²³⁵U, which is a concentration sufficient for current nuclear reactors ...

A heat pump is actually a bit like a refrigerator. While a fridge takes heat from its interior and heats the room in which it stands, a heat pump takes heat from the external heat reservoir to heat the interior of the house. A suitable reservoir can be the surrounding air, the ground on which the house stands or a water tank ...

The smallest amount of fissile material in which a fission chain reaction can take place is called the critical amount. Most of the neutrons produced in it during fission continue to participate in fission. This allows the reaction to run continuously. The critical amount depends on the type of fissile material, its concentration and the shape in which it is arranged ...

Ionizing radiation is all around us. It arises from the decay of atoms in our surroundings and in our own bodies or it comes to us from space as cosmic radiation. We call materials containing unstable isotopes radioactive, but since everything around us is slightly radioactive, we have not developed senses to detect radioactivity ...

To be honest, I haven’t experienced this but it’s probably because I don’t sunbathe much. I don’t know if the winter tan is also related to the skiing/mountain activities. If this is indeed the case, I think it has two causes ...

It would certainly be possible but we would need either a better flashlight or a bigger magnifying glass. About 1,000 W/m² of energy reaches the Earth from the Sun. If the Moon reflects roughly 20% of the falling sunlight, we would need a 5x better magnifier (i.e. a magnifier with a 5x larger surface, i.e. a 2.3x larger radius) ...

The movements of bodies in the central gravitational field are described by Kepler’s laws, of which only law 3 has the form of a formula. Isaac Newton used Kepler’s laws to formulate (his) law of gravity ...

When we tap the glass, we can hear a sound. The pitch (frequency) of this sound depends on the material and shape of the glass. By tapping, we make the glass vibrate, this vibration is transferred due to impacts of the glass to air molecules and spreads through the air to our ear ...

Horse power was introduced by James Watt to be able to approximate the power of the steam engine. Simply put, by determining the horsepower of a horse and comparing it to a steam engine, he could say: “My steam engine will replace 10 horses”. This way it was easy for everyone to imagine and was certainly well thought out in terms of marketing ...

All photos are basically rotated, more precisely inverted. This is because the display system of the camera/mobile phone has to create an actual image on the sensor. If we want to use a lens/mirror to create a real image, it will always be inverted. In the same way, the lens in our eye creates an inverted image on the retina and the brain “turns” it around ...

I believe that the content of radioactive substances in food depends mainly on where we get the food from. Radioactive materials enter food from its surroundings. Plants and mushrooms get radioactivity from the soil they grow in and animals have radioactive particles in them either from food (plants) or air/water ...

In general, energy that we can’t use turns into heat and that’s what happens with lightning energy. It is necessary to realize that lightning is actually a slightly stronger example of an electric current (we call it an electric discharge) and therefore the same applies to it as, for example, to an electric kettle, a light bulb or a washing machine ...

I don’t think that there would always be a difference between the photos in the morning and in the evening, I would rather expect that we can observe something similar from time to time. And I would guess especially in the summer ...

Gravitational force acts on every body. If we want to lift a body, we must exert a greater force in the opposite direction. Buoyant force helps us in water — it has an upward direction and therefore if we want to lift a body in water, the sum of our buoyant force and our force must be greater than the force of gravity ...

Our eye perceives only a (very small) part of electromagnetic waves and we call this part light. This wave is described by its frequency (in visible light, the frequency corresponds to a certain colour). The colour of the body depends on its temperature (if we are talking about light sources) ...