Hlavní část přípravy vystoupení proběhla distančně, studenti v mezinárodních dvojicích diskutovali připravované pokusy, sdíleli nápady. Bylo třeba se domluvit na přípravě obdobné sady pomůcek ve Finsku a pak v České republice, protože převoz potřebných pomůcek letecky  by byl v mnoha případech nemožný a ve většině případů komplikovaný. 

Studenti si pokusy vzájemně popisovali, sdíleli fotografie pomůcek i nahrávky pokusů. Výsledkem byla příprava první verze všech pokusů finskými partnery.

Část komunikace je zveřejněna níže:

The main part of the preparation for the performance took place remotely, with students in international pairs discussing the planned experiments and sharing ideas. It was necessary to agree on preparing a similar set of equipment in Finland and then in the Czech Republic, as transporting the required materials by air would be in most cases complicated and in many cases impossible 

Students described the experiments to each other, shared photos of the equipment, and recorded videos of the experiments. The result was the preparation of the first version of all the experiments by the Finnish partners.

Part of the communication is published below:

An induction cooker, as the name suggests, operates on the principle of electrical induction. Beneath the glass plate lies a copper coil through which an alternating electric current passes, generating a rapidly changing magnetic field above the cooker. The cooking vessel placed on the hob must be made of metal. The quickly changing magnetic field induces an electric current in the vessel, which is then transformed into heat.

If a bulb with a copper wire is placed above the cooker, it will flicker occasionally. Placing a pot on the wire, without directly touching the hob, will cause the bulb to glow steadily. This effectively creates a transformer, with the primary coil residing in the induction cooker and the secondary coil in the bulb. The pot's presence is not strictly necessary for the bulb to flicker, but it serves to maintain the cooker's operation.

- Electromagnetic induction -

• What is an electromagnetic induction?

Electromagnetic induction describes the process of generating an electromotive force and an electric current in a conductor in a changing magnetic field. Michael Faraday is thought to be the discoverer of induction and to this day we use Faraday’s law of induction. It states that whenever there is a relative motion between a conductor and a magnetic field or a change in the magnetic field strength through a conductor, an electromagnetic force is induced. If the circuit is complete, induced voltage causes an electric current to flow in a close circuit.

• How does an induction cooker works?

The induction cooker consists of a coil of copper wire beneath the cooking surface. When an electric current flows through this coil, it generates an alternating magnetic field. When we put a suitable cooking vessel on a cooktop, this changing magnetic field induces an electric current in the bottom of the vessel, according to Faraday’s law of induction. The coil in the induction cooker has generally many turns compared to the cooking vessel. It forms a transformer that steps down the voltage and steps up the current. The induced electric current generates resistive heating within the vessel due t the resistance of the material (also called Joule heating). The vessel becomes hot and transfers the heat to its contents by heat conduction.

The cooking vessel need to be made of magnetic materials, for example iron or stainless steel. Non-magnetic materials like aluminium do not work on an induction cooker.

• Why does the cooktop of an induction cooker remain relatively cold?

Unlike traditional gas or electric stoves, an induction cooker does not heat the cookware through conduction. It uses electromagnetic induction to directly heat the cooking vessel. Hence the cooktop will heat by heat conduction from the cookware but on its own it has no reason to become hot. It has generally a heat-proof glass-ceramic surface which is not magnetic at all. An electromagnetic induction does not apply to it.

• How is it possible to light a bulb on an induction cooker?

It is possible to use an induction cooker not only for generating heat. Another coil is necessary for that. We have to connect the bulb to the coil to create a closed circuit. Then we place it within the proximity of the cooktop. The electromagnetic field generated by the cooker’s induction coil would induce a small electric current in the circuit of the bulb. If we decrease the intensity of the induction cooker, the bulb will alternately light up and go out. That is because an induction cooker does not adjust the power intensity directly, instead it adjusts the power by controlling the intervals between inductions.

EXPERIMENTS – Electromagnetic induction

• Cooking with banknote between the cooktop and the cooking vessel

Hypothesis: We can cook with objects between the cooktop and the cookware because the cooking surface is not directly heated.

Materials: any banknote, an induction cooker, a suitable cooking vessel

Procedure: First, put the banknote on the induction cooker. Then cover it with the cooking vessel filled with water. Let the water boil. Take out the banknote. Make it is entirely undamaged.

Results:The banknote was indeed completely fine.

• Cooking egg half on the cooktop and half on the vessel

Hypothesis: The half we place on the vessel will cook, while the other half, placed on the cooktop, will remain raw.

Materials: an induction cooker, enough eggs, a suitable cooking vessel preferably without edges

Procedure: Place an egg on the induction cooker so one its half is situated on the vessel while the other half is lying directly on the cooktop. Watch what is happening.

Results: The hypothesis was right; only one half of the egg has cooked.

• Lighting a bulb using an induction cooker

Hypothesis: If we connect a bulb to coil, we will create circuit in which we can generate electric current using an induction cooker.

Materials: an induction cooker, conductive wire, a little bulb, a multimeter

Procedure: First, create a coil with the conductive wire. Then, using the multimeter, measure the voltage on the coil. Fing a bulb which needs approximately as much voltage as you measured. Connect the bulb to the coil. Bring it really close to the induction cooker. Watch if the bulb lights up.

Results: The bulb did light up, even though just a little bit. When we decreased the intensity of the induction cooker, we could see the bulb change from shining to going out.

Lenz's law - script

We know how electromagnetic induction works: if we change the magnetic field around a conductor, it causes the induction of an electric current inside a closed circuit. But this is actually not the entire thing – when the electric current starts flowing through the conductor, it creates its own magnetic field. So let's take a look at how these magnetic fields interact with each other.

We have two rings hanging on strings – one is from aluminium and one from copper. We can see that the magnet doesn't stick to the rings, but take a look at what happens when we take a magnet and move it around the rings.

[Experiment – Lenz´s law and metal strings]

We can see that when we move the magnet closer to the ring, we actually make the ring go away. By moving the magnet around the ring, we caused electromagnetic induction – we induced an electric current inside the ring, and as we said, this induced current created its own magnetic field. This field pushed against the magnet, and so it made the ring go away. We actually know that this happens every time: the magnetic field that was created by the induced electric current always acts against the change that caused the induction. This phenomenon is called Lenz's law.

Let's try to do something similar, but with a little twist. What if instead of using a metal ring, which is basically a wire, we tried to use a massive metal object?

We have a metal cup sitting on a needle so that it can spin. Let's see what happens when we move the magnet above the cup.

[Experiment – Lenz´s law and a spinning cup]

We can see that the cup starts to spin. The principle here is very similar to the last experiment: by moving the magnet, we induce an electric current in the cup. But since the cup is not a wire but a  massive metal object, the electrons inside it don't move in a single loop but in multiple different loops at once. This way of electron movement is called eddy currents. But in this situation, eddy currents actually work the same way as a single loop – they also create a magnet field around the cup, so Lenz's law works here as well.

Let's change the experiment one more time. Now, we are going to drop the magnet through this aluminium pipe to see if Lenz´s law also applies in this situation.

[Experiment – a magnet falling through an aluminium pipe]

We can see that it hes taken the magnet unusually long to fall through the pipe. And this is again due to Lenz's law. The falling magnet induces eddy currents inside the pipe, and as we know, the magnetic field around these currents should push against the change that caused the induction. But this change was the falling magnet, so pushing against the change means pushing the magnet upwards, which makes it slow down.

Franklin’s Bell Experiment

Hello everybody, my name is Anna, and I'll be showing you an experiment called Franklin's Bell. It's called Franklin's Bell after Benjamin Franklin, who invented and popularized it in the 18th century. He had one of these to tell if a lightning storm was coming near. But probably the most important thing about Franklin’s Bell is that it was the first time that electrical energy was converted into mechanical energy. So, how did Benjamin Franklin use it and how did it work?

He had a lightning rod on his house, which was connected to a bell inside the house. I'm a poor student from the Czech Republic, so instead of the bell, I brought an empty can, which will serve me just the same. (I will place the can on the table.) Right next to that bell, he had another bell (I will place the other can close to the first one) that was connected to the ground. The ground will be demonstrated by a polystyrene foam board, which has the same electrical qualities. (Under one can, I will place the foam board.) In between the bells, there was a metal ball attached to a string. Instead of the metal ball, I'll use a pull tab from a can, which I tie to a thread and hang on a wooden stick. (I will insert the wooden stick through the pull tab of the can.) And that’s the whole setup.

Then, Benjamin Franklin only waited for a storm to come. If big clouds or a storm passed by, the lightning rod would get that positive charge, and the bells would start ringing. Now, since I probably don't have a lightning storm coming up, I'll simulate it with a plastic rod. I’ll electrify the plastic rod with a piece of cloth and bring it close to the side of one can.

How it worked is that as this can become exceedingly positive, the negative charges inside the pull tab would become closer to this side, while the positive charges would be over here. This causes the pull tab to be attracted to the positively charged can. So, the pull tab would swing and hit this can. As it would hit the can, the pull tab would also become positively charged. This means that now it would be repelled, and since this can is connected to the ground or basically has a negative charge, it would quickly swing to it and discharge itself through this can. And then, this process would repeat again and again, making the bells ring.

With this relatively simple experiment, Franklin was able to predict that a storm was coming. Nowadays, we all probably have the weather forecast downloaded on our mobile phones, so the experiment probably has no use for us. But if your phone dies or you simply can't access the internet, it could come in handy. Plus, most forecasts (at least those we have in the Czech Republic) are pretty unreliable, so with this experiment, you'll have 100% accuracy.

script PLASMA BALL

Hi, we have prepared for you a couple of experiments with this plasma ball. This is a plasma

ball. How does it work? Normally gas doesn't conduct current. But there's a vacuum in the

plasma ball and it's full of low pressure gas. So there's a discharge and we can see lightning.

What if I touch the plasma ball? What do you think? Please raise your hand.

A. The color of the lightning changes.

B. The lightning will disappear from the plasma ball.

C. The lightning will follow my finger.

D. Nothing will happen.

(experiment)

Lightning follows my finger because it's made up of electrons and they're lazy. They always

want to take the shortest route. They also want out of the plasma ball because there's too

many of them. So my finger is the best way for them to get away. They run a finger along the

surface of my body to the ground.

Can you turn on the light? Yes?

Me too I use a switch to turn the light on.

And can you turn on the fluorescent lamps? Even if it's not plugged into an outlet

I do.

(experiment)

How is that possible? The fluorescent lamp contains mercury vapor. The electrons from the

cathode start to ionize the mercury vapor. Some of the energy is converted into ultraviolent

light, which is invisible to us. That's why all fluorescent lamps are white. It's the special

fluorescent dye on the lamps that makes the light visible. The plasma ball works in a similar

way. The alternating voltage at the centre creates electromagnetic waves, and the arcs of

plasma act as antennae, meaning that the extent of the electromagnetic field surrounding

the ball is significantly larger than the bounds of the glass globe. Bringing the fluorescent

tube near to the plasma ball allows the electrons inside to be accelerated by this field, and

those moving electrons constitute an electric current, which causes the bulb to light up.

We can compete. Who does the light prefer?

(experiment)

Electrons are lazy and take the route with the smaller electrical resistance. That's why she

won. Who wins depends on our electrical resistance; one of us is more electrically resistant

Each gas emits a different light. We can verify this by using discharge lamps with different

gases.

(experiment)

There is a changing electric field around the plasma ball, we can use a jack connected to a

speaker to listen to the changing electrical field (experiment)