Keith Mack
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage. This law is named after German physicist Georg Ohm, who first experimentally verified the law in 1827. The law is expressed by the equation V = I x R, where V is voltage, I is the current, and R is the constant of proportionality, or resistance, measured in ohms. In some cases, it is necessary to use smaller units for current and resistance, such as milliamps (mA) and milliohms (mΩ). One ohm is equal to 1,000 milliohms, so it is possible to convert between the units using the formula: electrical resistance in ohms = electrical resistance in milliohms / 1,000.
| Characteristics | Values |
|---|---|
| Ohm's Law | The current through a conductor between two points is directly proportional to the voltage |
| What it states | The current that flows through most conductors is directly proportional to the voltage applied to it |
| Formula | V = I x R |
| Units | V (voltage), I (current), R (resistance) |
| Other units | mA (milliamps), kΩ (kilohms) |
| Milliamps | Used when the amp is too large |
| Kilohms | Used when the ohm is too small |
| Milliohms | Equal to 1/1000 of an ohm |
| Exceptions | Ohm's Law does not apply when increasing the current raises the temperature, e.g. in a lightbulb filament |
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What You'll Learn
Ohm's Law and electrical resistance
Ohm's Law, discovered by Georg Simon Ohm and published in his 1827 paper, "The Galvanic Circuit Investigated Mathematically", states that the current through a conductor between two points is directly proportional to the voltage. This is true for many materials, over a wide range of voltages and currents, and the resistance and conductance of electronic components made from these materials remain constant.
Ohm's Law can be expressed using a number of equations, usually all three together:
- To calculate voltage, V: V = I × R
- To calculate current, I: I = V/R
- To calculate resistance, R: R = V/I
In these equations, V stands for voltage, I stands for current, and R stands for resistance. Voltage is measured in volts, current is measured in amps, and resistance is measured in ohms.
The ohm is the SI-derived unit for electrical resistance in the metric system. One ohm is equal to 1,000 milliohms, and one milliohm is equal to 1/1,000 of an ohm. Milliohms and ohms are both units used to measure electrical resistance. The ohm is also the resistance between two points of an electrical conductor transmitting a current of one ampere when the electrical potential difference is one volt between the points.
Ohm's Law is a simple and useful tool for analyzing electric circuits. It is the basis for the analysis of any electrical circuit and is used often in the study of electricity and electronics. By knowing this law, you understand the concept that underlies the operation of everyday devices such as lightbulbs, stereos, and phones.
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Converting milliohms to ohms
Yes, you can use 'milli' in Ohm's Law. In fact, it is necessary to use the correct units for the three quantities in Ohm's Law (voltage, current, and resistance) to get accurate results. While voltage can be measured in volts, and current in either amps or milliamps, resistance can be measured in either ohms or milliohms.
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage. This law can be expressed using a number of equations, usually all three together:
- To calculate voltage, V: V = I × R
- To calculate current, I: I = V/R
- To calculate resistance, R: R = V/I
Milliohms and ohms are both units used to measure electrical resistance. One milliohm is equal to 1/1,000 of an ohm, or 0.001 ohms. This means that to convert milliohms to ohms, you divide the electrical resistance in milliohms by 1,000 (or move the decimal point three places to the left). For example, 5,000 milliohms divided by 1,000 equals 5 ohms.
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Calculating voltage, current and resistance
Ohm's Law is a fundamental principle in electrical engineering and physics, describing the relationship between voltage, current, and resistance in an electrical circuit. It states that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance between them.
Ohm's Law can be expressed using a number of equations, usually all three together:
- To calculate voltage (V), the equation is V = I x R
- To calculate current (I), the equation is I = V/R
- To calculate resistance (R), the equation is R = V/I
It's important to note that the right units must be used for the three quantities in Ohm's Law; otherwise, calculations will yield incorrect values. For example, current is typically measured in amps, symbolised by the letter "I", while resistance is measured in ohms, symbolised by the letter "R". Voltage is measured in volts, symbolised by "E" or "V".
Ohm's Law can be extended to include the concept of electrical power, which is the rate at which electrical energy is converted to another form of energy, such as heat, light, or mechanical energy. Power in an electrical circuit is typically measured in watts (W).
In resistive circuits, Joule's Law can be combined with Ohm's Law to produce alternative expressions for the amount of power dissipated.
Additionally, you can use the VIR triangle to help remember the three versions of Ohm's Law. For instance, to calculate voltage, cover up the "V" in the VIR triangle, leaving "I" and "R". This gives you the equation V = I x R.
Online Ohm's Law calculators are also available, which can solve for any of the variables in the Ohm's Law equation using various units of measurement.
Regarding the use of "milli" in Ohm's Law, milliohms (mΩ) and ohms (Ω) are both units used to measure electrical resistance. One ohm is equal to 1,000 milliohms, so you can convert between the two units using this formula: electrical resistance in ohms = electrical resistance in milliohms / 1,000.
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Using the VIR triangle
The VIR triangle is a visual representation of Ohm's Law, which describes the relationship between voltage, resistance, and current. The triangle is a useful mnemonic for recalling the three equations used to calculate voltage, current, and resistance.
The triangle is formed by the letters V, I, and R, which represent voltage, current, and resistance, respectively. By covering the letter of the variable you want to find, you can derive the equation for it. For example, to calculate voltage, cover V, which leaves I and R, indicating that voltage is calculated by multiplying current and resistance (V = I x R). Similarly, to calculate current, cover I, which leaves V and R, indicating that current is calculated by dividing voltage by resistance (I = V/R). Finally, to calculate resistance, cover R, leaving V and I, indicating that resistance is calculated by dividing voltage by current (R = V/I).
It's important to note that the units of measurement must be consistent when using the VIR triangle and Ohm's Law. For example, for most electronic circuits, current is measured in milliamps (mA) and resistance in kilohms (kΩ). Using the wrong units will result in incorrect calculations.
The VIR triangle is a simple yet powerful tool for solving problems related to Ohm's Law, which is one of the most basic and important laws of electric circuits.
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Limitations of Ohm's Law
Ohms can be abbreviated as Ω; for example, 1 ohm can be written as 1 Ω. Milliohms are a multiple of ohms and are used to measure electrical resistance. One ohm is equal to 1,000 milliohms, and one milliohm is equal to 1/1,000 of an ohm. Milliohms can be abbreviated as mΩ, so 1 milliohm can be written as 1 mΩ.
Ohm's Law states that the current flowing between two points on a conductor is proportional to the voltage and inversely proportional to the resistance. The law applies to circuits that contain only resistive elements, with no capacitors or inductors. It is used for finding the resistance of a circuit and also for knowing the voltage and current of the circuit.
However, Ohm's Law has some limitations. It is not applicable in unilateral networks, which allow current to flow in one direction and consist of elements like diodes and transistors. It also does not apply to nonlinear networks, where parameters such as resistance, inductance, and capacitance vary with voltage and current and are not constant.
Additionally, Ohm's Law assumes that physical conditions, such as temperature, remain constant. In reality, factors like temperature can affect the resistance of a conductor and, thus, impact the accuracy of calculations based on Ohm's Law. It is also important to use the correct units when applying Ohm's Law to ensure accurate calculations.
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Frequently asked questions
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage.
The formula for Ohm's Law is V = I * R, where V is voltage, I is the current, and R is the resistance.
Yes, you can use milliamps in Ohm's Law. It is important to use the correct units for the three quantities in the law (voltage, current, and resistance). For example, you can use V, A, and Ω, or V, mA, and kΩ, but you must not mix these sets of units.
One ohm is equal to 1,000 milliohms, so you can convert between the two using a simple formula: electrical resistance in ohms = electrical resistance in milliohms / 1,000.
