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Basic definitions & laws revised

1) Current is the movement of electric charge along a definite path. The S.I. unit of current is the ampere. 2) Voltage, also called potential, is the amount of work required to move a unit of electric charge between two points. The S.I. unit of voltage is the volt. 3) For current to flow, a complete circuit with a potential difference is needed, similar to how water flows from a higher water tank to a lower one when they are connected.

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BASIC DEFINITIONS & LAWS Syed Hasan Saeed 1 Syed Hasan Saeed, Integral University, Lucknow
CURRENT: The movement of electric charge along a definite path is known as current. S.I. Unit of current is Ampere (A) VOLT: If 1 joule of work is required to put 1 coulomb of charge on a charged body, the body is said to have a potential of 1 VOLT. Consider the following diagram Syed Hasan Saeed, Integral University, Lucknow 2 BASIC DEFINITIONS & LAWS 5 Volts 1 Volts 1 coulomb charge A B Work done required to raise 1 coulomb charge up to point A =1 joule Potential of A =1 Volt Work done required to raise 1 coulomb charge up to point B = 5 joule Potential of B = 5 Volt
BASIC DEFINITIONS & LAWS Let, W = Energy required to move positive charge from one point to other (joules) Q = Positive charge (coulomb) Then V= W/Q J/C V is known as the voltage or potential and its unit is volt. POTENTIAL DIFFERENCE: Electrical energy or current flows from higher potential to lower potential. Therefore for flow of current a potential difference is necessary. This can be easily understand by the diagram of two water tanks. Fig. (a) : when two water tanks are not connected, then no water flows. Fig. (b) : when two water tanks having water of same level and they are placed at same level then no water flows from either tank to other. Syed Hasan Saeed, Integral University, Lucknow 3
Water tanks Syed Hasan Saeed, Integral University, Lucknow 4 BASIC DEFINITIONS & LAWS Tank A Tank B Fig. (a) No water flows Fig. (b) No water flows Tank A Tank B
BASIC DEFINITIONS & LAWS Water tanks Tank A is at higher level and tank B is at lower level, the water flows from tank A to Tank B i.e from higher level to lower level. Similarly, if two bodies are at different potentials, no current flows between them, but when two bodies are connected by a wire, the current will flow and try to equalize the potentials. Syed Hasan Saeed, Integral University, Lucknow 5 Tank A Tank B
BASIC DEFINITIONS & LAWS Syed Hasan Saeed, Integral University, Lucknow 6 Potential 100 volts Potential 50 volts Body “A” Body “B” Potential 100 volts Potential 50 volts Current Body “A” Body “B” Two bodies A and B are at different potentials but no current will flow Two bodies A and B are at different potentials current will flow from Body A to Body B
BASIC DEFINITIONS & LAWS Therefore for flow of current from one body to other or from one point to other in a circuit, not only must there be a potential difference but also an electrical connection between them. Therefore the potential difference (P.D) between two points is the energy required to move one coulomb of charge from one to the other. Its unit is volt. Thus if two bodies have a P.D. of 50 Volts, 50 joule of work done will require to move 1 coulomb from one to the other body. VOLTAGE DROP: The voltage drop between two points of an element is a decrease in energy in transferring a charge from one point to other point. Syed Hasan Saeed, Integral University, Lucknow 7
BASIC DEFINITIONS & LAWS RESISTNCE: Resistance is property of material due which it opposes the flow of current through it. It is denoted by R and unit is Ohm (Ω). INDUCTANCE: Inductance is property of material due which it opposes any change in current passing through it. It is denoted by L and unit is Henry (H). CAPACITANCE: Capacitance is property of an element due which it opposes any change in voltage across it. It is denoted by C and unit is Farad (F). Syed Hasan Saeed, Integral University, Lucknow 8 R L C
BASIC DEFINITIONS & LAWS OHM’S LAW: Ohm’s law states that the current through any conductor is directly proportional to the potential difference between its terminals. It is assumed that the physical conditions of the conductor do not change. I α V voltage I = (1/R) V Or, V = IR Where “R” is known as resistance of the conductor. EXAMPLE: An Electric iron takes a current of 3.7 A from 230 V supply. What is its resistance? SOLUTION: According to Ohm’s Law R = Syed Hasan Saeed, Integral University, Lucknow 9 Current = Constant V I = = 62.16 ohms230 3.7
BASIC DEFINITIONS & LAWS POWER: Rate of doing work is known as power. Also defined as rate of change of energy. Also, Power = rate of change of energy But I = Q/t Therefore, P = VI Also, I = V/R Then P = V2 / R Also. V = IR Then P = I2R Syed Hasan Saeed, Integral University, Lucknow 10 Power = Energy Time Unit : J/s i.e Watt Power = Work Time = W t = VQ t
hasansaeedcontrol@gmail.com https://syedhasansaeed.gnomio.com/ https://shasansaeed.yolasite.com/ Syed Hasan Saeed, Integral University, Lucknow 11