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- A quick revision by Short notes



  • It is a fundamental property of an atom. It may be positive or negative.
  • Like charges repel each other and opposite charges attract.
SI unit of charge is coulomb. 1 Coulomb charge= Charge present on approx. electrons Charge on 1 electron C . The formula to determine the amount of charge is:

Where, Q = Charge(total), n = No. of electrons, e = Charge on 1 electron


The current is defined as the rate of flow of charge through a particular conductor. The SI unit of current is Ampere (A). The device to measure current is Ammeter. The connection of an ammeter in an electric circuit is as shown below:
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Important points to measure current:

  • Ammeter has low resistance and is always connected in series.
  • The direction of current is taken opposite to the flow of electrons as electrons.

Potential Difference

Potential Difference (V) is the work done to move a unit charge from one point to another. It is given by the formula:

Definition of Volt

When 1 Joule work is done in carrying one Coulomb charge then the potential difference is 1 volt.
SI unit of Potential difference = Volt (V)

Ohm's Law

The potential difference across the two points of a metallic conductor is directly proportional to the current passing through the circuit provided that temperature remains constant.

Mathematical expression for Ohm's law:

is a constant called resistance for a given metal.

The V-I characteristics of an ohmic conductor:

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Symbols of Some Commonly Used Components in Circuit

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Resistors in Series

When two or more resistors are connected end to end, the arrangement is called a series combination.
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Total/resultant/overall/effective resistance in series.

Current through each resistor is the same.

Resistors in Parallel

In a parallel connection of resistors, all points on one side of the resistor are connected together and all points on the other side are connected together.
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Total/resultant/overall/effective resistance in Parallel:

The voltage across each resistor in a parallel circuit remains the same.

Electric Power

Electric power is the amount of electrical energy consumed per unit time. Amount of power consumed in a device is proportional to the current flowing in the device. The unit of electric power is watt.
Electrical power is given by:

Heating Effect of Electric Circuit

Heat is produced inside a conductor due to the movement of the charged particles inside it. This heat produced is given by the formula shown below: