Electric current and potential difference: formulas and SI units

ELECTRICITY

• In this chapter mainly if you are good with the formulas then don't worry about anything. one or two problems will come in the exam soo if study formulas why should you waste those marks. yes, of course it is hard to memorize those long formulas but once you did trust me this chapter will be too easy. before that lets go through what all we are studying in this chapter.
• ELECTRIC CURRENT
• first and main thing to understand, what it actually means by current or electric current. it simply means the rate of flow of charges. charges? what does than mean..? it is actually a measured quantity which takes care of the electric properties of a substance. we have a small formula to find current, charge or time. I = Q/R electric current is a vector quantity.
• Here I is represented as current, charge as Q and time as T. The SI units of these quantities are ampere, coulomb, seconds.
• So, ampere can be defined as-
• When one coulomb of charge flows through a conductor in one second then the amount of charge passing through the conductor will be one ampere.
• 1A=1C/1s
• ammeter is a device used to measure electric current.
• Q=ne
• electrons = 1.6x10^-19

Slide 2

• POTENCIAL DIFFERENCE
• the amount of work done to move one one unit of charge to other. V=W/Q
• here, v is potential difference, w is amount of work done, and q is charge.
• the SI unit of potential difference is volt.
• the SI unit of work is joule.
• 1V= 1J/1C
• the potential difference is measured by device called voltmeter.
• ELECTRIC POTENCIAL
• it is the amount of work done to move a unit charge from infinity to a particular point.
• OHMS LAW
• according to sr. john simon ohm, he says that the current flowing through the conductor is proportional to the potential difference across the conductor when the physical features like temperature, pressure remains the same.
• I=V/R
• RESISTANCE
• it is a property of conductor to resist its flow of charges through it.
• SI unit of resistance is ohm.
• FACTORS ON WHICH RESISTANCE DEPEND
• a) directly proportional to length of the wire
• b) inversely proportional to the area of cross section
• R=(rho) l/a
• rho is a proportionality constant known as resistivity of the material of conductor.
• RESISTIVITY
• the resistance offered by a wire of unit cross section and unit length.
• SI unit of resistivity is ohm meter.
• SERIES COMBINATION
• Rs = R1+ R2 + R3
• PARALLEL COMBINATION
• 1/Rp = 1/R1 + 1/R2 + 1/R3

Slide 3

• HEATING EFFECT OF ELECTRIC CURRENT
• When an electric current is passed through a wire, the wire gets heated up and its temperature rises. this property is called heating effect of electric current.
• eg electric toaster, light bulb etc
• SI unit of energy is joules
• formulas:
• W= I^2 Rt
• W= VIt
• W= V^2/R . t
• POWER
• it is the rate of doing work.
• P= E/t
• P=VI
• P=I^2 R
• P=V^R
• SI unit of power is watt
• watt is defined as the power consumed by the devise, when 1 ampere of current passes through it when the potential difference of it is 1v.