To describe the processes in physics and chemistry, there are a number of laws and relationships obtained experimentally and by calculation. Not a single study can be carried out without a preliminary assessment of the processes by theoretical relationships. Faraday's laws are applied in physics and chemistry, and in this article we will try to briefly and clearly tell you about all the famous discoveries of this great scientist.
Content:
- Discovery history
- Electrodynamics
- Electrolysis
Discovery history
Faraday's law in electrodynamics was discovered by two scientists: Michael Faraday and Joseph Henry, but Faraday published the results of his work earlier - in 1831.
In his demonstration experiments in August 1831. he used an iron torus, on the opposite ends of which a wire was wound (one wire per side). He supplied power from a galvanic battery to the ends of one of the first wires, and connected a galvanometer to the terminals of the second. The design was similar to a modern transformer. Periodically turning on and off the voltage on the first wire, he observed bursts on the galvanometer.
The galvanometer is a highly sensitive instrument for measuring the strength of small currents.
Thus, the effect of the magnetic field formed as a result of the flow of current in the first wire on the state of the second conductor was depicted. This impact was transmitted from the first to the second through the core - a metal torus. As a result of research, the influence of a permanent magnet that moves in the coil on its winding was also discovered.
Then Faraday explained the phenomenon of electromagnetic induction in terms of lines of force. Another was a device for generating direct current: a copper disk rotated near a magnet, and a wire sliding along it was a current collector. This invention is called the Faraday disk.
Scientists of that period did not recognize Faraday's ideas, but Maxwell took research into the basis of his magnetic theory. In 1836 g. Michael Faraday established relationships for electrochemical processes, which were called Faraday's Laws of Electrolysis. The first describes the ratio of the mass of the substance released at the electrode and the flowing current, and the second the ratio of the mass of a substance in solution and released at the electrode, for a certain amount electricity.
Electrodynamics
The first works are used in physics, specifically in the description of the operation of electrical machines and devices (transformers, motors, etc.). Faraday's law states:
For a circuit, the induced EMF is directly proportional to the magnitude of the speed of the magnetic flux that moves through this circuit with a minus sign.
This can be said in simple words: the faster the magnetic flux moves through the circuit, the more EMF is generated at its terminals.
The formula looks like this:
Here dФ is the magnetic flux, and dt is a unit of time. It is known that the first time derivative is speed. That is, the speed of movement of the magnetic flux in this particular case. By the way, the source of a magnetic field (a coil with a current - an electromagnet, or a permanent magnet) and a circuit can move.
Here, the flow can be expressed by the following formula:
B is the magnetic field and dS is the surface area.
If we consider a coil with tightly wound turns, with the number of turns N, then Faraday's law looks like this:
Magnetic flux in the formula for one turn, measured in Weber. The current flowing in the circuit is called inductive.
Electromagnetic induction is the phenomenon of current flow in a closed loop under the influence of an external magnetic field.
In the formulas above, you may have noticed the signs of the modulus, without them it has a slightly different form, such as it was said in the first formulation, with a minus sign.
The minus sign explains Lenz's rule. The current arising in the circuit creates a magnetic field, it is directed in the opposite direction. This is a consequence of the law of conservation of energy.
The direction of the induction current can be determined by the right hand rule or gimbal, we examined it in detail on our website.
As already mentioned, thanks to the phenomenon of electromagnetic induction, electrical machines, transformers, generators and motors, work. The illustration shows the current flow in the armature winding under the influence of the stator magnetic field. In the case of a generator, when its rotor rotates by external forces, an EMF arises in the rotor windings, the current generates a magnetic field directed in the opposite direction (the same minus sign in the formula). The more current consumed by the generator load, the greater this magnetic field, and the more difficult it is to rotate.
And vice versa - when current flows in the rotor, a field arises, which interacts with the stator field and the rotor begins to rotate. With a load on the shaft, the current in the stator and in the rotor increases, while it is necessary to ensure switching of the windings, but this is another topic related to the design of electrical machines.
At the heart of the operation of the transformer, the source of the moving magnetic flux is an alternating magnetic field arising from the flow of alternating current in the primary winding.
If you want to study the issue in more detail, we recommend watching the video, which easily and easily explains Faraday's law for electromagnetic induction:
Electrolysis
In addition to research on EMF and electromagnetic induction, the scientist made great discoveries in other disciplines, including chemistry.
When current flows through the electrolyte, ions (positive and negative) begin to rush to the electrodes. Negative ones move towards the anode, positive towards the cathode. In this case, a certain mass of a substance is released on one of the electrodes, which is contained in the electrolyte.
Faraday conducted experiments, passing different currents through the electrolyte and measuring the mass of the substance deposited on the electrodes, deduced patterns.
m = k * Q
m is the mass of the substance, q is the charge, and k depends on the composition of the electrolyte.
And the charge can be expressed in terms of the current over a period of time:
I = q / t, then q = i * t
Now you can determine the mass of the substance that will be released, knowing the current and the time that it has flowed. This is called Faraday's First Law of Electrolysis.
Second law:
The mass of a chemical element that settles on the electrode is directly proportional to the equivalent mass element (molar mass divided by a number that depends on the chemical reaction in which substance).
In view of the above, these laws are combined into the formula:
m is the mass of the substance that was released in grams, n is the number of transferred electrons in electrode process, F = 986485 C / mol - Faraday number, t - time in seconds, M molar mass substance g / mol.
In reality, due to various reasons, the mass of the emitted substance is less than the calculated one (when calculating taking into account the flowing current). The ratio of the theoretical and real masses is called the current efficiency:
BT = 100% * msettlement/ mtheor
And finally, we recommend that you view a detailed explanation of Faraday's law for electrolysis:
Faraday's laws made a significant contribution to the development of modern science, thanks to his work, we have electric motors and generators of electricity (as well as the work of his followers). The work of EMF and the phenomena of electromagnetic induction gave us most of the modern electrical equipment, including loudspeakers and microphones, without which it is impossible to listen recordings and voice communication. Electrolysis processes are used in the electroplating method of coating materials, which has both decorative and practical value.
Related materials:
- Joule-Lenz law
- The dependence of the resistance of the conductor on temperature
- Ohm's law in simple words
