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Ohm’s law shows the relationship between potential difference and electric current. If current flows through a conductor, the current is proportional to the voltage applied to the conductor. Ohm is the SI unit of electrical resistance. Famous German physicist Georg Simon Ohm worked on resistance in 1826 and published in 1827, in the book Die galvanische Kette, mathematician bearbeitet. Ohm’s law was named in honour of the physicist Georg Simon Ohm. So, we will discuss what Ohm’s law is, application of Ohm’s law, limitations of Ohm’s law, Ohm’s law magic triangle, verification of Ohm’s law, water pipe analogy for Ohm’s law.
What is Ohm’s law?
Ohm’s Law was put forward by George Ohm in 1789. According to this Law, the current that flows through the circuit varies proportionally to the voltage difference across the terminal of the cell.
V ∝ I
V = IR
Here, R is the constant known as resistance. It is the obstruction created by the flow of current. The unit of resistance is Ohm. It increases with the temperature with the length of the wire and decreases with the increase of the area of the wire.
On plotting the voltage and current on a graph, we get the graph as shown below. We get a positive and straight slope, thus indicating a constant increment of current with the voltage.
Ohm’s Law is one of the most significant laws in electricity. For studying the behaviour of electric circuits, Ohm’s Law is one of the most widely used rules.
However, not all conductors strictly follow Ohm’s law. Various conductors show variations and do not have a straight slope for the V-I graph.
Electrical Resistance
The resistivity of a material is a fundamental element in determining the electrical resistance of a conductor, and it is the part of the resistance equation that accounts for different materials’ characteristics.
In order to explain electrical resistance we can use a simple example. Assume the flow of electrons (current electric carriers) across a wire is represented by marbles flowing down a ramp: If you put obstacles in the way of the ramp, you’ll encounter resistance. As marbles collided with the barriers, they lost some of their energy, causing the total flow of marbles down the ramp to slow down.
The effect of going through a paddle wheel on the speed of a current of water is another comparison that might help you grasp how resistance affects current flow. Again, energy is transferred to the paddle wheel, causing the water to move more slowly.
The reality of current flow through a conductor is closer to the marble example because electrons travel through the material but are slowed by the lattice-like structure of the nucleus of the atoms.
A conductor wire’s electrical resistance is defined as:
R = LA
Where is the material’s resistivity (which varies depending on its composition), L is the conductor wire’s length, and A is the wire’s cross-sectional area (in square meters). According to the equation, a longer conductor has a higher electrical resistance, while one with a larger cross-sectional area has lower resistance.
Factors affecting the resistance:
- Nature of the substance:
According to their resistivity, materials are classified as insulators, conductors, and semiconductors, among others.
Insulators have high resistance, whereas conductors have very low resistance.
- Temperature:
As the temperature of the material rises, the resistance increases as well.
- Cross-sectional area :
A wire’s resistance R is inversely related to its cross-sectional area A, as follows:
R α 1/A…. (1)
It signifies that a thicker wire has less resistance than a thinner wire. We get the following when we combine equations R α L….. and (1)
R α L/A
R=ρL/A
This equation represents the relationship between the resistance of a conductive wire, length of the wire, cross-sectional area of wire and resistivity of the wire.
Conclusion
As we have discussed Ohm’s law and resistance of a wire. Ohm’s law states that the current that flows through the circuit varies proportionally to the voltage difference across the terminal of the cell. Resistance is the opposition of the current flow in a conductor. The resistance of a wire is depends on the nature of substance, length of the wire, cross-sectional area and temperature
The Zener diode goes through several different stages or zones, which are described here.
(a).The Zener diode receives forward voltage, which is positive voltage across its anode and cathode terminals, on the right half of the characteristics curve. In this region, the diode is forward biased. The current is tiny for a while during this time until the voltage hits a particular point, known as the threshold voltage, at which point it spikes exponentially up.
(b).When it comes to Zener diodes, the left half of the characteristics curve is more essential. The Zener diode receives positive voltage across its cathode and anode terminals at this point. In this area, the diode is reverse biased. When receiving reverse voltage, the current is initially quite low. The diode only has a little current running through it, known as the leakage current. When it reaches the breakdown voltage, the current skyrockets. Because of its extreme peaks, this current is known as the avalanche current.
(c).The breakdown voltage point is very significant, not only because of the avalanche current, but also because once the Zener diode’s voltage reaches this point, it remains constant at that voltage, even if the current across it increases dramatically. This makes the Zener diode valuable in voltage regulation applications.
(d).When the voltage across a Zener reaches this breakdown voltage, also known as a Zener diode’s Zener voltage, VZ, the voltage that a Zener lowers across itself will not grow. If a Zener diode has a Zener voltage of 5.1V and the voltage feeding the diode is about 5.1V, the Zener will drop 5.1V across its terminals. Even if the voltage (and current) powering it continues to increase, say to 12V, the Zener diode will keep its Zener voltage of 5.1V.
(e).This is the single most significant feature of a Zener diode, which permits it to operate as a voltage regulator in a circuit, as previously stated. Even if the voltage or current in the circuit increases, the voltage lowered across a Zener will not surpass its breakdown or Zener voltage, as shown by the I-V characteristics curve above.
Zener Breakdown
The failure is caused by the Zener breakdown phenomenon, which occurs when the voltage falls below 5.5 volts. It could also have an effect on ionisation that happens at 5.5 Volt. Both processes provide the same results and hence do not necessitate separate circuitry. However, the temperature coefficient for each process is different. The temperature coefficient of the Zener effect is negative, whereas the temperature coefficient of the impact effect is positive. Since the two temperature effects are nearly equivalent, they cancel each other out. Because of this, Zener diodes are the most stable throughout a large temperature range.
Avalanche Breakdown
The reverse saturation current is responsible for the avalanche breakdown mechanism. The PN-junction is made up of P-type and N-type materials. At the point where the P and N-type materials meet, a depletion area forms.
The P and N-type materials in the PN junction are not ideal, and they contain impurities, such as electrons in the p-type material and holes in the N-type material. The depletion region’s width varies. Their width is determined by the bias given to the P and N region’s terminals.
The electrical field across the depletion zone is increased by the reverse bias. When a strong electric field prevails across the depletion, the minority charge carrier’s velocity increases as it crosses the depletion region. These carriers collide with the crystal’s atoms. The charge carrier pulls the electrons off the atom due to the forceful collision.
The electron-hole pair is increased as a result of the collision. The electron-hole pairs are swiftly split and smash with the other atoms in the crystals as they induce in the high electric field. The process is ongoing, and as the electric field increases, reverse current begins to flow in the PN junction. The Avalanche Breakdown is the name for this process. The junction cannot revert to its previous position after the failure because the diode has entirely burned out.
Conclusion
A Zener diode is a semiconductor device made of silicon that allows current to flow in both directions. When a particular voltage is reached, the diode’s special, highly doped p-n junction is designed to conduct in the other direction.The Zener diode has a well-defined reverse-breakdown voltage at which it begins to conduct current and may operate in reverse-bias mode indefinitely without damage. Furthermore, the voltage drop across the diode remains constant over a wide range of voltages, making Zener diodes ideal for voltage regulation.
