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

SESSION 2012/ CO 4 Ability to analyze basic electrical circuitry.

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 3 SESSION 2012/2013

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

Concept of Electricity SESSION 2012/ 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. Greek word electrons which mean “amber” which is a petrified tree resin. This phenomenon is called “static electricity”

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

Electric charge SESSION 2012/ Electrostatics is the study of interaction between electric charges which are not moving. Two types of electric charges: Carried by particles called electrons. Positive Carried by particles called protons. Negative

Electric charge SESSION 2012/ 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

Conservation of electric charge SESSION 2012/ 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.

Conservation of electric charge SESSION 2012/ 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.

Insulators and conductors SESSION 2012/ 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.

Coulomb’s law SESSION 2012/ 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.

Coulomb’s Law SESSION 2012/ 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 r Q1Q1 Q2Q2

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

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

Example 2 SESSION 2012/ Which charge exerts the greater force? These two forces have equal magnitude. F 21 = F 12. The force on Q 2 exerted by Q 1 is the same as the force on Q 1 exerted by Q 2 except that Q 1 and Q 2 are reversed. These two forces have equal magnitude. F 21 = F 12. The force on Q 2 exerted by Q 1 is the same as the force on Q 1 exerted by Q 2 except that Q 1 and Q 2 are reversed.

Example 3 SESSION 2012/ 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 Q1 = µC 0.30 m0.20 m Q3 = µCQ2 = +3.0 µC F = - F32 + F31 = -2.7 N N = N

Electric field SESSION 2012/ 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.

Electric field SESSION 2012/ 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.

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

Electric field SESSION 2012/ 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.

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/

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/

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/

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/

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/

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/

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/

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: SESSION 2012/ Fixed ResistorVariable Resistor

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/

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 ρ represents 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/

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

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/

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

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

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/

Series and Parallel Wiring Voltage, V of the battery, V = V 1 + V 2 + V 3 = IR 2 + IR 3 V = I (R 1 + R 2 + R 3 ) Equivalent resistance in the circuit, Req = R 1 + R 2 + R 3 SESSION 2012/

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 I 1 and I 2. SESSION 2012/

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 SESSION 2012/ I = I 1 + I 2 I 1 = V/R 1 and I 2 = V/R 2

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 SESSION 2012/ I = I 1 + I 2 + I 3 = V/R 1 + V/R 2 + V/R 3 = V(1/R 1 + 1/R 2 + 1/R 3 ) 1/R eq = V(1/R 1 + 1/R 2 + 1/R 3 )

Example Two resistors of 200 Ω are 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/

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/