LECTURE of Current Electricity and .pptx

What is current electricity discuss in the pptx

1. CURRENT ELECTRICITY Dr Nahid Ullah (PT) DPT , MSPT* IPMR KMU

2. ELECTRIC CURRENT A flow of charge from one place to another. The unit is Ampere, which equal to a flow of 1 coulomb per second. Moving charges as current: Its described as a stream of moving charges. May range very small currents such as the nerve impulses to a large as the solar wind emitted by the sun. There must be a “net” flow of charges towards one direction

3. Electric current in a conductor An isolated conductor in absence of electric potential contains free flowing electrons but no electric current. An isolated conductor in absence of electric potential contains free flowing electrons but no electric current.

4. A conductor connected to a dry cell or battery has the necessary electric potential to influence the flow of charges towards one direction, hence producing current.

5. Electric Current Electric current (I ) is defined as the amount of charges passing through the conductor per unit of time. Its unit is coulomb per second (C/s), also called ampere (A). I =Q/t Where: I = Current (ampere, A) Q = Charge (coulomb, c) t = Time (seconds)

6. Numerical Questions A current of 3 mA is flowing through a wire for 1 minute. What is the charge flowing through the wire ? ? ? A current of ……mA is flowing through a wire for 2 minute. If the charge of 20 columb is flowing through the wire .

7. DIRECTION OF CURRENT In reality, electric current are movement of electrons along the conductor. For historical reason, current is treated as flow of positive charges to the direction opposite that of the actual movement of electrons.

8. These positive charges are not actual particles. They are called holes, vacant spaces where there should be an electron. The charge of a hole is +1.6 x 10-19 C. Electrons are known as negative charge carriers. Holes are known as positive charge carriers.

9. Electric Resistance Property of the conducting medium that weakens the transmission of electric current. Denoted as R and its unit is Ohm (Ω). R = ρ L/A Where: R = Resistance (Ohm, Ω) ρ = resistivity ( Ω m) L = Length of the wire (m) A = cross-sectional area of a wire(m2)

10. Numerical Questions A piece of 1.0 m wire has a resistance of 0.19 ohms. Calculate the resistivity of the wire. The cross-sectional area of the wire is 0.5 mm2 ??? A piece of 0.5 m wire has a resistance of 0.25 ohms. Calculate the resistivity of the wire. The cross-sectional area of the wire is 0.12 mm2 ??? A piece of 0.8 m wire has a resistance of 0.15 ohms. Calculate the resistivity of the wire. The cross-sectional area of the wire is 0.15 mm2 ???

11. Resistance Ohms Law states that when a voltage (V) source is applied between two points in a circuit, an electrical current (I) will flow between them encouraged by the presence of the potential difference between these two points. The amount of electrical current which flows is restricted by the amount of resistance (R) present. In other words, the voltage encourages the current to flow (the movement of charge), but it is resistance that discourages it Resistance in a conductor depends on nature, length and area of cross section of the conductor. .

12. Nature of material: Some materials create least hindrance and hence are called good conductors. Silver is the best conductor of electricity. While some other materials create more hindrance in the flow of electric current, i.e. flow of electrons through them. Such materials are called bad conductors. Bad conductors are also known as insulators. Hard plastic is the one of the best insulators of electricity.

13. Length of conductor Resistance R is directly proportional to the length of the conductor. This means, Resistance increases with increase in length of the conductor. This is the cause that long electric wires create more resistance to the electric current. Thus, Resistance (R) ∝ length of conductor (l) An electric current flows when electrons move through a conductor, such as a metal wire. The moving electrons can collide with the ions in the metal. This makes it more difficult for the current to flow, and causes resistance . The resistance of a long wire is greater than the resistance of a short wire because electrons collide with more ions as they pass through. The relationship between resistance and wire length is proportional .

14. Length of Conductor

15. Cross sectional Area The resistance of a thin wire is greater than the resistance of a thick wire because a thin wire has fewer electrons to carry the current. The relationship between resistance and the area of the cross section of a wire is inversely proportional .

16. Cross sectional area

17. Resistivity Resistivity ( ρ) Measure of how much resistance a material possesses against electric current. Intrinsic property of a material that depends on its electronic structure .

18. Conductivity Measure of how the material is capable of conducting electricity. Reciprocal of resistivity.

19. OHM’S LAW Ohm's Law deals with the relationship between voltage and current in an ideal conductor. This relationship states that: The potential difference (voltage) across an ideal conductor is proportional to the current through it.  The constant of proportionality is called the "resistance", R . Ohm's Law is given by: V = I R

20. where V is the potential difference between two points which include a resistance R. I is the current flowing through the resistance. Material that obeys Ohm's Law is called " ohmic " or " linear"  because the potential difference across it varies linearly with the current.

21. The Resistor The resistor is a passive electrical component to create resistance in the flow of electric current. In almost all electrical networks and electronic circuits they can be found. The resistance is measured in ohms. Resistors are used for many purposes. A few examples include delimit electric current, voltage division, heat generation..

22. Direct and Alternating Current There are two different types of current in widespread use today. They are direct current, abbreviated DC, and alternating current, abbreviated AC.

23. Alternating current Abbreviated AC, pushes the electrons back and forth, changing the direction of the flow several times per second. The generators used in power plants to produce electricity for your home are designed to produce alternating current. You've probably never noticed the lights in your house actually flicker as the current changes direction because it happens too fast for our eyes to detect.

24. Direct Current Direct current is electric current that only flows in one direction. A common place to find direct current is in batteries. A battery is first charged using direct current that is then transformed into chemical energy. When the battery is in use, it turns the chemical energy back into electricity in the form of direct current. Batteries need direct current to charge up, and will only produce direct current.

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