Table of Contents
Electrical Resistance Formula
Resistance is a fundamental concept in physics that quantifies the opposition encountered by an electric current flowing through a conductor. It is denoted by the symbol “R” and is measured in ohms (Ω). The resistance of a conductor depends on its material, length, cross-sectional area, and temperature.
Electrical Resistance Definition:
Electrical resistance is a measure of the opposition encountered by an electric current as it flows through a conductor. It quantifies how effectively a material or device resists the flow of electric charge. Resistance is influenced by factors such as the material’s composition, length, cross-sectional area, and temperature.
Electrical Resistance Formula:
Ohm’s Law states that the current passing through a conductor is directly proportional to the voltage applied across it and inversely proportional to its resistance. Mathematically, Ohm’s Law can be expressed as:
V = I x R
Where:
V represents the voltage across the conductor in volts (V).
I represent the current flowing through the conductor in amperes (A).
R represents the resistance of the conductor in ohms (Ω).
Rearranging the formula, we can solve for resistance:
R = V / I
The resistance formula shows that resistance is equal to the ratio of voltage to current. It indicates the amount of potential difference required to produce a certain current through a conductor. The higher the resistance, the greater the voltage needed to maintain a specific current.
Electrical Resistance Unit:
The unit of electrical resistance is the ohm (Ω). It is named after the German physicist Georg Simon Ohm, who formulated Ohm’s Law, which relates voltage, current, and resistance in an electrical circuit.
Factors Affecting Electrical Resistance:
Resistance depends on various factors. The resistivity of the material is a crucial property that determines the resistance. Materials with high resistivity, such as rubber or glass, have high resistance, while materials with low resistivity, such as copper or silver, have low resistance.
The length and cross-sectional area of the conductor also affect resistance. Longer conductors have higher resistance, while wider or thicker conductors have lower resistance. This relationship is described by the formula:
R = (ρ x L) / A
Where:
ρ (rho) represents the resistivity of the material in ohm-meters (Ω·m).
L represents the length of the conductor in meters (m).
A represents the cross-sectional area of the conductor in square meters (m²).
Temperature also plays a role in resistance. Most materials increase their resistance as temperature rises, although this effect varies among materials.
Solved Examples of Electrical Resistance Formula:
Example 1: A circuit has a voltage of 12 volts applied across a resistor, and a current of 2 amperes flows through it. Calculate the resistance.
Solution:
Given:
Voltage (V) = 12 volts
Current (I) = 2 amperes
Using Ohm’s Law:
R = V / I
R = 12 V / 2 A
R = 6 ohms
Therefore, the resistance of the circuit is 6 ohms.
Example 2: A wire has a length of 10 meters and a cross-sectional area of 2 square millimetres. The resistivity of the material is 1.7 x 10-8 ohm-meters. Calculate the resistance of the wire.
Solution:
Given:
Length (L) = 10 meters
Cross-sectional area (A) = 2 mm2 = 2 x 10-6 m2
Resistivity (ρ) = 1.7 x 10-8 ohm-meters
Using the resistance formula:
R = (ρ x L) / A
R = (1.7 x 10-8 ohm-meters x 10 meters) / (2 x 10-6 m2)
R = (1.7 x 10-7 ohm-meters) / (2 x 10-6 m2)
R = 0.085 ohms
Therefore, the resistance of the wire is 0.085 ohms.
Frequently Asked Questions on Electrical Resistance Formula:
What is the formula for electrical resistance?
R = V / I where: R represents the resistance (measured in ohms, Ω), V is the voltage across the component or circuit (measured in volts, V), and I is the current flowing through the component or circuit (measured in amperes, A). Ohm's Law states that the current flowing through a conductor is directly proportional to the voltage applied across it and inversely proportional to the resistance of the conductor. The resistance is a measure of how much the conductor opposes the flow of electric current.
What are the 4 factors that affect resistance?
The four factors that affect resistance are: Material: Different materials have different resistivities, which determine their resistance. Materials with higher resistivities offer greater resistance to the flow of electric current. Length: The length of the conductor affects resistance. As the length increases, the resistance also increases. A longer path offers more resistance to the flow of electrons. Cross-sectional area: The cross-sectional area of the conductor influences resistance. A larger cross-sectional area allows for easier flow of electrons, reducing resistance. Temperature: Temperature affects resistance, especially in conductors. Most materials experience an increase in resistance with an increase in temperature. However, some materials, like semiconductors, may exhibit different behaviour. These factors collectively determine the resistance of a conductor and have practical implications in electrical circuits and systems.
What is the SI unit of resistance?
The SI unit of resistance is the ohm (Ω). It is named after the German physicist Georg Simon Ohm, who formulated Ohm's law. The ohm is defined as the resistance through which a current of one ampere will flow when a potential difference of one volt is applied across it.
What does Ohm's law state?
Ohm's Law states that the current flowing through a conductor is directly proportional to the voltage applied across it and inversely proportional to its resistance. In mathematical terms, it can be expressed as V = IR, where V is the voltage, I is the current, and R is the resistance. This law provides a fundamental relationship between these three quantities in electric circuits.
Where is Ohm's law used?
Ohm's Law is used in various applications related to electricity and electronics. It is commonly used in circuit analysis and design to determine the relationship between voltage, current, and resistance. It is a fundamental principle in the field of electrical engineering and is used in the design and operation of electrical devices, such as resistors, conductors, and power sources. Ohm's Law also plays a crucial role in troubleshooting electrical circuits and calculating values for components in practical applications.
What are the 3 commonly used units of resistance?
The three units commonly used to measure resistance are ohm (Ω), kilohm (kΩ), and megohm (MΩ). The ohm is the standard unit of resistance in the International System of Units (SI). The kilohm is equal to 1,000 ohms, and the megohm is equal to 1,000,000 ohms. These units are used to express resistance values in different ranges, with ohms typically used for small values, kilohms for medium values, and megohms for large values.
Are there any limitations to Ohm's Law?
Ohm's Law assumes that the resistance remains constant, and that the conductor follows Ohm's Law linearly. In reality, there may be variations in resistance due to factors such as temperature changes or non-linear behavior in certain devices. Additionally, Ohm's Law is most accurate for metallic conductors and may not be as accurate for other types of materials.
Why is it called electrical resistance?
Electrical resistance is called so because it refers to the property of a material to resist the flow of electric current through it. When an electric current passes through a material with resistance, it encounters opposition, causing a reduction in the flow of electrons. This opposition or hindrance to the flow of current is known as resistance. The term electrical is used to specify that it pertains to the domain of electricity and circuits. Resistance plays a crucial role in determining the behaviour of electrical components and the overall functioning of electrical systems.
How does temperature affect resistance?
For most materials, including metals, resistance increases with an increase in temperature. This relationship is known as positive temperature coefficient. However, there are a few exceptions, such as certain semiconductor materials, which exhibit negative temperature coefficients.
