Has it ever happened to you that, after charging or having turned on an electrical device, you have noticed it hot? What is going through the cable and the appliance? Electricity, but… Why is it hot?
In this article we propose an experiment on this phenomenon, so important in the transport of electricity: the Joule Effect, which could be defined as "the heat energy produced by an electric current passing through a conductive material" or "the amount of energy heat produced by an electric current flowing through the conductor and its resistance.
How do you experiment with the Joule effect?
Attention: The preparation of this experiment is not complicated, but you do have to be careful, since the materials that we will use as conductors can burn when passing the electric current.
Before we start, we have to prepare a small assembly to simulate an electrical tower. This will make it easier for us to carry out the different parts of the experiment.
We will join the two toothpicks to a piece of polystyrene, sticking them into it, leaving a separation of about 10 centimeters. Next, we will join the cables with insulating tape, in the central part, so that the ends remain free.
Experiment 1: materials and the Joule effect
For this first experiment, we will need:
- A 1.5V battery.
- Two wires of different materials: one of copper and the other of plastic or nylon.
- The assembly carried out (our electrical tower).
We will connect one of the wires to the crocodile clips and the other ends of the cable to each terminal of the battery. We have to observe what happens when the current passes through the plastic or nylon thread, lightly touching it with the finger. We will notice that it is cold.
Now we will replace the plastic or nylon wire with the copper one, checking that the latter is hotter, using a piece of polystyrene.
What happens and how do we explain it?
More than 100 years ago, a physicist named James Prescott Joule discovered that when an electric current flowed through a conductor, heat was generated in it, due to the effect of the resistance of the material to the passage of the electric current.
Said resistance of the material occurs because the electrical intensity, or current, is the movement of electrons through a conductor. These electrical charges, having mass and speed, have kinetic energy, which is released in the form of heat when the charges collide with the atoms of the conductor.
With the copper wire (conductive material), the circuit is closed and electric current flows, thus appearing the Joule effect.
However, this does not appear when we insert the plastic wire into the circuit, since it is an insulating material that does not allow current to flow.
Experiment 2: Factors involved in the Joule effect
Now we will need:
- One 1.5 V battery and one 4.5 V battery (or three 1.5 V batteries connected in series),
- Wires of different types and conductive materials.
First, we will connect the 1.5V battery to our peculiar electrical tower and we will interchange the different wires of conductive material to identify which of them gives off more heat, touching them with a piece of polystyrene.
Subsequently, we will replace the 1.5V battery with the 4.5V one, and we will repeat the process to check the energy dissipated in the form of heat. We can also see if the cable changes color, if it emits smoke… or if nothing happens.
What happens to the same wire when subjected to more voltage? For the same stack… Do all the threads behave in the same way?
Why does it happen and how do we explain it?
The Joule effect depends on the resistance offered by the conductor to the flow of current (resistivity), as well as the amount of current flowing through the circuit.
Thus, if our electric generator increases the voltage (by adding batteries in series), the heat released in our circuit will be greater.
And, logically, the greater the resistance opposed by the material, we will appreciate the greater Joule effect. In other words, the iron wire heats up before the copper wire, which is a better conductor
Experiment 3: Let's experiment with the material section
Finally, we suggest that you experiment with only 2 threads of the same material, but of different section or thickness.
In the assembly (electric tower), and with the 4.5V battery, we will first connect a wire with a larger section and we will bring a piece of polystyrene to it. Then we will change it for the finest thread and we will bring a piece of polystyrene to it.
What happens to the polystyrene in both situations? Which circuit gets hotter?
Why does it happen and how do we explain it?
We note that the thick wire barely gives off heat. However, the thin one gets much hotter, even cutting the polystyrene. This phenomenon is due to the fact that, having less space, the electric charges impact more with the atoms of the conductive material, giving off more heat energy.
The Joule effect and the transport of electricity
In the same way that it happens in our experiment, the Joule effect is present whenever there is an electrical charge in motion. Although it is not always a harmful phenomenon (incandescent light bulbs work under this phenomenon, for example), it is usually a dissipated energy that is always sought to be minimized, such a reduction in electrical transport over long distances being key.
To do this, in the conductive cables the factors that we have analyzed in this experiment are modified:
- Good electrical conductors, such as copper or aluminum, are used instead of others that may offer more electrical resistance.
- Thanks to electrical transformers, the electrical intensity that circulates through the cables is reduced.
- It is transported in triphasic networks (plus cables).
In future experiments we will discover ways to take advantage of this electrical phenomenon, as well as other equally important ones.
