1 / 42

PDT 180 ENGINEERING SCIENCE

PDT 180 ENGINEERING SCIENCE. ELECTRICITY AND CIRCUITRY. MISS MUNIRA MOHAMED NAZARI SCHOOL OF BIOPROCESS ENGINEERING UNIMAP. TOPIC OUTLINE. Concepts of electricity, Insulators and conductors, Electric fields, Coulomb’s Law. Concepts of electric current, Ohm’s Law, Electric power,

ganit
Télécharger la présentation

PDT 180 ENGINEERING SCIENCE

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. PDT 180ENGINEERING SCIENCE ELECTRICITY AND CIRCUITRY MISS MUNIRA MOHAMED NAZARI SCHOOL OF BIOPROCESS ENGINEERING UNIMAP

  2. SESSION 2012/2013

  3. TOPIC OUTLINE • Concepts of electricity, • Insulators and conductors, • Electric fields, • Coulomb’s Law. • Concepts of electric current, • Ohm’s Law, • Electric power, • Series and parallel wiring SESSION 2012/2013

  4. BACIS CONCEPTS OF ELECTRICITY OBJECTIVES To define electricity To identify electrical charges To define electrical fields SESSION 2012/2013

  5. Concept of Electricity Greek word electrons which mean “amber” which is a petrified tree resin. • Electricity • If an amber rod is rubbed with a piece of cloth, the amber attracts small pieces of leave or dust. • If u rub a plastic ruler and bring it close to some tiny pieces of papers, the ruler will eventually attract the papers. This phenomenon is called “static electricity” SESSION 2012/2013

  6. Concept of Electricity • Object can be charged by rubbing. SESSION 2012/2013

  7. Electric charge • Electrostatics is the study of interaction between electric charges which are not moving. • Two types of electric charges: SESSION 2012/2013

  8. Electric charge • The force between the charges can be either attraction or repulsion. • Unit for charge is Coulomb, C where; • Mass of electron = • Mass of proton = or SESSION 2012/2013

  9. Conservation of electric charge • Law of conservation of electric charge states that the net amount of electric charge produced in any process is zero. • It means that in any process, electric charge cannot be created or destroyed. • It can be transfer to one object to another. • For example, when a plastic ruler is rubbed with a paper towel, the plastic acquires a negative charge and the towel an equal number of positive charges. The charges are separated but the sum of the two is zero. SESSION 2012/2013

  10. Conservation of electric charge • Can be illustrated using a simple model of atom. • A neutral atom contains an equal number of protons and electrons. • If the number of protons and electrons are not same, the atom will have a net positive or negative charge. This atom is called an ion. SESSION 2012/2013

  11. Insulators and conductors • Materials can be either insulating or conducting materials. • Insulating • Conductors • Semiconductors Material contains electrons which are not free to move through the material. Eg: glass & wood Material contains electrons are free to move in the material. Eg: steel & gold Material in which there are a few free electrons and the material is a poor conductor or electricity. Eg: silicon & carbon. SESSION 2012/2013

  12. Coulomb’s law • Experiment shows that the electric force between two charges is proportional to the product of the charges and inversely proportional to the distance between them. SESSION 2012/2013

  13. Coulomb’s Law • Coulomb’s Law states that two point charges exert a force (F) on one another that is directly proportional to the product of the magnitudes of the charges (Q) and inversely proportional to the square of the distance (r) between their centers. • We can rewrite the Coulomb’s Law in term of equation as: k is a constant which has a value of Q1 Q2 r SESSION 2012/2013

  14. Coulomb’s Law • The force is along the line connecting the charges and is attractive if the charges are opposite, and repulsive if they are the same. SESSION 2012/2013

  15. Example 1 • Find the magnitude and direction of the force on the electron. SESSION 2012/2013

  16. Example 2 • Which charge exerts the greater force? These two forces have equal magnitude. F21 = F12. The force on Q2 exerted by Q1 is the same as the force on Q1 exerted by Q2 except that Q1 and Q2 are reversed. SESSION 2012/2013

  17. Example 3 • Three charges in a line. • Three charged particles are arranged in a line as shown below. Calculate the net electrostatic force on particles 3 (the -4.0 µC on the right) due to the other two charges. 0.30 m 0.20 m - + - Q1 = - 8.0 µC Q2 = +3.0 µC Q3 = - 4.0 µC F = - F32 + F31 = -2.7 N + 1.2 N = - 1.5 N SESSION 2012/2013

  18. Electric field • An electric field present if an electric charge experiences an electric force at any particular point in space. • In order to visualize the path taken by a charged particle in an electric field; electric field lines (lines of force) are drawn. • These line start on a positive charge and end on negative charge. SESSION 2012/2013

  19. Electric field • The number of field lines starting (ending) on a positive (negative) charge is proportional to the magnitude of the charge. • The electric filed is stronger where the field lines are closer together. SESSION 2012/2013

  20. Electric field • Electric dipole : two equal charges, opposite in sign. • The electric field between two closely spaced, oppositely parallel plates is constant. SESSION 2012/2013

  21. Electric field • Summary of field lines: • Field lines indicate the direction of the field; the field is tangent to the line. • The magnitude of the field is proportional to the density of the lines. • Field lines start on positive charges and end on negative charges; the number is proportional to the magnitude of the charge. SESSION 2012/2013

  22. BACIS CONCEPTS OF CIRCUITRY OBJECTIVES To define electric current, voltage, resistance and electric power To define electric circuit To analyze the series and parallel wiring. SESSION 2012/2013

  23. Concepts of Electric Current • An electric current exists whenever electric charge flows from the battery terminals through a region or circuit like a light bulb circuit as shown in figure below. • The magnitude of the current is measures in amperes (A). SESSION 2012/2013

  24. Concepts of Electric Current • Above figure represent symbol of electric current flow. • What actually happened is that free electron charges moving from the battery terminal and flow or crossing through the wire. The flow charge is known as electric current. SESSION 2012/2013

  25. Concepts of Electric Current • Definition • Electric current in a wire is defined as the net amount of charge that passes through the wire per unit time at any point. • The average current is defined as: • Unit for electric current = ampere (A)  (coulomb/sec) SESSION 2012/2013

  26. Example : Electric charge flow • A steady current of 2.5 A flows in a wire for 4.0 min. Calculate charge passed through any point in the circuit. How many electrons would this be? SESSION 2012/2013

  27. Ohm’s Law • Ohm’s law discusses on resistance in electrical circuit. • Electric resistance is the resistance of electrical current flow. Electrical resistance is important since it can control the amount of current flow. Ohm defines resistance, R as the ratio of the voltage applied across the circuit. • Resistance, R of the piece of material or wire is given as • Unit for resistance, R = ohm (Ω) SESSION 2012/2013

  28. Example : Resistance in a bulb • A small flashlight bulb draws 300 mA current from 1.5 volt battery. Determine the resistance of the flashlight bulb. R = V/I = 1.5 V / 0.30 A = 5.0 Ω SESSION 2012/2013

  29. Ohm’s Law • Resistors • All electrical devices have resistance to the flow of current. • For instance, the connecting wires of a circuit have resistance. However, in electronic devices, resistors are used to control the amount of current. • The types of resistor varied from fixed resistor to variable resistor. When we draw a circuit diagram, we indicate the resistance or the resistor in the circuit by the symbol: Fixed Resistor Variable Resistor SESSION 2012/2013

  30. Ohm’s Law • Resistance factors in a wire. • Wire in an electric circuit can be thick or thin wire and the resistance is not the same. There ate 3 factors that affect the resistance of a wire which are: • Length of wire • Cross sectional area • Resistivity of the wire. • It was found that the relationship of these factors is as SESSION 2012/2013

  31. Ohm’s Law • The longer the wire, the higher the resistance and if the cross sectional areas of the wire is smaller, the resistance is also higher. • Meanwhile, the symbol ρrepresents the resistivity of the material. Resistivity of the material depends on the property of the material. • For conductors, the resistivity value is higher compared to insulators. • Meanwhile, resistivity for semiconductor materials depends on the temperature of the material. SESSION 2012/2013

  32. Electric Power • Power as in kinematics, is the energy transformed by a device per unit time. • Unit for power = watt, W SESSION 2012/2013

  33. Electric Power • If the devices have resistors, then the electrical power of the device is transformed into other form of energy. • For instance, a toaster, irons, stoves, etc become hot when provided with electrical power. • If we want to express the power in term of resistance, then the formula becomes as: SESSION 2012/2013

  34. Example : Flashlight • Determine the resistance of the bulb • Determine the power if V = 1.2 volt V = 1.5 Volt P = 0.15 Watt I = P/V = 0.1 A R = V/I = 15 Ω P = V²/R = 0.096 Watt SESSION 2012/2013

  35. Series and Parallel Wiring • There are 2 methods by which connection can be made: • Series wiring • Parallel wiring SESSION 2012/2013

  36. Series and Parallel Wiring • Series wiring • Means that the devices are connected in such a way that there is the same amount of current flow through each device. • In the series wiring, if one of the devices is disconnected, the current will not be able to flow through another device, which means that the device is interrupted too. • Because of the series wiring, the voltage supplied by the battery id divided between the devices. • For instance, if we have 3 resistors, then, the voltage is divided between the 3 resistors. SESSION 2012/2013

  37. Series and Parallel Wiring • Voltage, V of the battery, V = V1 + V2 + V3 = IR2 + IR3 V = I (R1 + R2 + R3) • Equivalent resistance in the circuit, Req = R1 + R2 + R3 SESSION 2012/2013

  38. Series and Parallel Wiring • Parallel wiring • Means that the devices are connected in such a way that the same voltage is applied across each device. • Parallel wiring is the most popular wiring method. This is because, if the current in one of the devices is interrupted (by opened or broken wire), then the current in the other devices are not interrupted. • In parallel circuit, the total current I that leave the battery break into each branch. • Eg: If we have two branches, then the current is I1 and I2. SESSION 2012/2013

  39. Series and Parallel Wiring • Total current is • Devices in parallel circuit each experience the same voltage from the main voltage (battery). Therefore, each of the current can be represented as I = I1 + I2 • I1 = V/R1 and I2 = V/R2 SESSION 2012/2013

  40. Series and Parallel Wiring • Similar to series circuit, we need to determine the equivalent resistance of circuit. This can be done by adding all the current in each branch. • For instance, in a 3 branch parallel circuit: • Therefore I = I1 + I2 +I3 = V/R1 + V/R2 + V/R3 = V(1/R1 + 1/R2 + 1/R3) 1/Req = V(1/R1 + 1/R2 + 1/R3) SESSION 2012/2013

  41. Example • Two resistors of 200 Ωare connected (a) in series and (b) in parallel to a 24.0 volt battery. Determine the equivalent resistance and the current through each resistor. SESSION 2012/2013

  42. Summary • A battery is a source of constant potential difference. • Electric current is the rate of flow of electric charge. • Conventional current is in the direction that positive charge would flow. • Resistance is the ratio of voltage to current: • Power in an electric circuit: SESSION 2012/2013

More Related