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MAHESWARI JAIKUMAR , profile picture
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ELECTRICAL RESISTANCE

Resistance is defined as the ratio of voltage to current in a circuit. Ohm's law states that voltage is directly proportional to current and resistance. The resistance of an object depends on the material it is made of, with insulators having high resistance and conductors having low resistance. Resistance also depends on size and shape, with resistance increasing as length increases or cross-sectional area decreases. Resistance is measured in ohms and resistance can be calculated using the resistance equation.

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DR.MAHESWARI JAIKUMAR maheswarijaikumar2103@gmail.com
DEFINITION • The electrical resistance of a circuit component or device is defined as the ratio of the voltage applied to the electric current which flows through it: • If the resistance is constant over a considerable range of voltage, then Ohm's law, I = V/R, can be used to predict the behavior of the material.
• Resistance is a measure of the opposition to current flow in an electrical circuit. • Resistance is measured in ohms, symbolized by the Greek letter omega (Ω). ... Conductors: Materials that offer very little resistance where electrons can move easily.
OHM’s LAW & RESISTANCE • Ohm's law states that the voltage or potential difference between two points is directly proportional to the current or electricity passing through the resistance, and directly proportional to the resistance of the circuit. The formula for Ohm's law is V=IR.
RESISTANCE EQUATION
FACTORS INFLUENCING RESISTANCE • The resistance of an object depends in large part on the material it is made of. • Objects made of electrical insulators like rubber tend to have very high resistance and low conductivity, while objects made of electrical conductors like metals tend to have very low resistance and high conductivity.
• This relationship is quantified by resistivity or conductivity. • The nature of a material is not the only factor in resistance and conductance, it also depends on the size and shape of an object because these properties are extensive rather than intensive.
• For example, a wire's resistance is higher if it is long and thin, and lower if it is short and thick. • All objects resist electrical current, except for superconductors, which have a resistance of zero.
MEASUREMENT OF RESISTANCE An instrument for measuring resistance is called an ohmmeter. Simple ohmmeters cannot measure low resistances accurately because the resistance of their measuring leads causes a voltage drop that interferes with the measurement, so more accurate devices use four-terminal sensing.
SUMMARY OF KEY POINTS No PROPERTY FACT 1 Definition Resistance is the physical property of a substance because of which it opposes the flow of current i.e. electrons. 2 Proportionality Resistance is directly proportional to the length and temperature while it is inversely proportional to the cross-sectional area of the material. 3 Symbol R 4 Formula R = V/I or, R = ρ(L/A) V = Voltage, I = Current, ρ = Resistivity 5 SI Units The SI unit of resistance is Ohms 6 Applications The property of resistance is used in several places like heaters, fuses, sensors, etc.
RESISTIVITY (ρ) • Resistivity is the physical property of a particular substance which is having particular dimensions. • Resistivity is only proportional to the nature and temperature of the particular material.
FORMULA TO CALCULATE RESISTIVITY ρ = (R×A)/L R = Resistance L= Length A = Cross-sectional area • The SI unit of resistivity is Ohms-meter.
DIFFERENCE • One of the major difference between the resistance and the resistivity of the material is that the resistance opposes the flow of free electrons whereas the resistivity is the property of the material which defines the resistance of the material having specific dimension.
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