Electricity
- Every atom as a whole is electrically neutral. Its total positive charge is equal to its total negative charge. Charges are produced by loss or gain of electrons.
- Charges in motion and current: Charges in motion constitutes current electricity. An electric current is the rate of flow of electric charge through a given cross section of a conductor. Charge flows from higher potential to lower potential. By convention the flow of charges is taken as the flow of positive charges. Negative charges flows from lower potential to higher potential.
- Electric potential: at a point in a field is the amount of work done in bringing a unit positive charge from infinity to that point along any arbitrary path.
- A positive charge in an electric field moves from higher potential to lower potential, while a negative charge moves from lower potential to higher potential.
- Potential difference: The amount of work done in moving a unit positive charge from a point of low potential to a point of high potential between the two points..
- Ohm's law: The current flowing through a metallic conductor is proportional to the potential difference applied between its ends, provided its temperature remains constant.
- Resistance: The property by virtue of which a conductor opposes the flow of charge in it is known as resistance. The resistance of a conductor depends directly on its length, inversely on its area of cross-section and also on the material of the conductor.
(i) Current in each resistor is the same.
(ii) Potential difference across each resistor is
different and is proportional to the resistance.
(iii) Equivalent resistance of the arrangement is\[\text{R}={{\text{R}}_{1}}+{{\text{R}}_{2}}+{{\text{R}}_{3}}\]. Effective resistance is greater than any individual resistance.
(iv) If 'n' wires, each of resistance R, are Connected in series, the effective resistance is nR.
(i) Currents in the resistors are in proportion to
the reciprocals of resistances.
(ii) Potential difference across each resistor is the
same.
(iii) Equivalent resistance of the arrangement is \[\frac{1}{R}=\frac{1}{{{\text{R}}_{1}}}+\frac{1}{{{\text{R}}_{2}}}+\frac{1}{{{\text{R}}_{3}}}\]Effective resistance is less than any individual resistance.
(iv)If 'n' wires each of resistance R, are connected in parallel, the equivalent resistance is R/n.
- Heating effects of electric current: The heat produced is proportional to the square of the current, the resistance of the wire and the time for which the current flows.
- Electric power Power is the rate of doing work or the rate at which energy is produced or consumed. The electrical energy produced or consumed per unit time is called electrical power.
