Chapter 1 DET10013 - Part 1 PDF

CHAPTER 1 Part 1 INTRODUCTION TO ELECTRIC CIRCUIT PREPARED BY:CAROLINE ANN MAI LEARNING OUTCOMES : 1.1 Know standard symbols for electrical components. 1.2 Understand the general features of cells and batteries. 1.3 Know electric current and quantity of electricity....

CHAPTER 1 Part 1 INTRODUCTION TO ELECTRIC CIRCUIT PREPARED BY:CAROLINE ANN MAI LEARNING OUTCOMES : 1.1 Know standard symbols for electrical components. 1.2 Understand the general features of cells and batteries. 1.3 Know electric current and quantity of electricity. 1.4 Know the main effects of electric current. 1.5 Understand resistance and resistivity 1.6 Understand Ohm’s Law. 1.7 Apply Ohm’s Law in circuit. 1.8 Understand series, parallel and series-parallel connections. 1.9 Apply series, parallel and series-parallel connections to dc circuit. 1.10 Understand Delta–Star transformation. 1.11 Apply the concept of Delta–Star transformation. 1.12 Understand electrical power and energy. Standard Symbols for electrical components General Features Of Cells And Batteries  E.M.F as Source of Electricity A source of energy (electric generator , battery) that can cause a current to flow in an electrical circuit or device measured in volts Symbol :E Unit : Volt (V) E.M.F = Electromotive Force CELLS vs BATTERIES Cells An electrochemical device that generates e.m.f through a chemical reaction process that converts chemical energy into electrical energy E.m.f produces direct current (dc) in a complete electrical circuit that has a potential difference and a load, connected by external wiring. + - Symbol  cont... Consists of two different types of electrodes that are held apart from each other and connected through a substrate called an electrolyte. The separation of +ve and –ve ions at electrodes inside the electrolyte creates the e.m.f or terminal output voltage of the cell and thus produces current when electrons move from the negative terminal to the positive terminal through an external circuit that is connected at both electrodes. Battery A battery is a device that is formed by a combination of two or more cells that are connected in a suitable manner to generate more voltage If an appliance is placed between its terminal the current generated will power the device. Symbol  Types of Batteries Primary Battery Secondary Battery ❖ non-rechargeable ❖ rechargeable battery / disposable battery battery ❖possess the ability to ❖ only be used once, if be recharged many the charge inside the times as long as the battery is available battery is not spoiled to operate the or damaged. device that uses it.  Secondary Battery Primary Battery  Comparison Between Primary And Secondary Cells Primary Cells Secondary Cells Cost to build is more Cost to build is cheaper expensive Current is irreversible Current is readily reversed Cannot be recharged Rechargeable Regular maintenance Disposable required Not ideally suited for heavy Superior high discharge rate load / high rate discharge / performance at heavy loads high performance Types of Cell Connection 1. Series Connection 2. Parallel Connection 3. Series – Parallel Connection  Series Connection Total e.m.f E T = E 1 + E2 + E3 + E 4 Current IT = I1 = I2 = I3 = I4  Example 1 Calculate total e.m.f. of the circuit below Total e.m.f., ET = E1 + E2 + E3 + E4 = 2.0 + 2.0 + 2.0 + 2.0 = 8V  Parallel Connection Total e.m.f E T = E 1 = E2 = E3 = E 4 Current IT = I1 + I2 + I3 + I4  Example 2 Calculate total e.m.f. of the circuit below Total e.m.f., ET = E1 = E2 = E3 = 2.0V Series - Parallel Connection  Example 3 Calculate total e.m.f. of the circuit below Total e.m.f. for series cells, ESeries = E1 + E2 + E3 + E4 = 2.0 + 2.0 + 2.0 + 2.0 = 8V Total e.m.f., ET = ESeries = 8V The effect of polarities If the source voltage, E are connected in series with the same polarities, the total of series source E0 will be the summation of each source voltage. If the source voltage, E are connected in series with the same polarities, the total of series source E0 will be the summation of each source voltage. E1 E2 E3 E1 E2 E3 E0 E0 E0 = E1 + E 2 + E 3 E0 = E 1 + E 2 - E 3  Example 4 Series Connection with same Polarities Calculate total e.m.f. of the circuit below Total e.m.f., ET = E1 + E2 =8+6 = 14V  Example 5 Series Connection with opposite Polarities Calculate total e.m.f. of the circuit below Total e.m.f., ET = E1 + E2 =8-6 = 2V https://padlet.com/carolineannmai/7wbysdrbbhgaf22t SELF-EXERCISE QUESTION: Calculate total e.m.f. of each cell's connection as follow. i) 5V 11V 4V B A ANSWER Answer: 20V 44V ii) 44V B A 44V ANSWER Answer: 44V https://padlet.com/carolineannmai/7wbysdrbbhgaf22t SELF-EXERCISE QUESTION: Calculate total e.m.f. of each cells connection as follow. iii) 4V 3V B 2V 5V A Answer: ANSWER7V 6V 1V iv) 4V 4V 4V B A ANSWER Answer: 120V 30 cells https://padlet.com/carolineannmai/7wbysdrbbhgaf22t SELF-EXERCISE QUESTION: Calculate total e.m.f. of each cell's connection as follow. v) 14V B A 20 cells 14V ANSWER Answer: 14V 14V 5V 5V 5V vi) B 5V 5V 5V A 5V 5V 5V ANSWER Answer: 50V 10 cells Electric current and quantity of electricity 1. Electric Current, I 2. Electric Charge, Q 3. Potential Difference, V 4. Resistor, R 5. Conductor  Electric current, I It can be defined as the rate of flowing charges over time. Current flows from positive terminal to negative terminal. Moving electric charge caused by moving free electrons. Symbol: I Unit : Ampere (A)  Equation I = dq / dt dq = changing of charge dt = changing of time For steady state condition I=Q/t I = current(ampere) Q = charge (coulomb) t = time (second) Electric charge, Q Electric charge consists of positive and negative charge. Symbol :Q Unit : Coulomb (C)  Example 6 If a current of 5 A flows for 2 minutes, find the charge transferred. Q = It = 5 x 2 x 60 = 600 C  Example 7 Find the current flow if 0.24 Coulombs of charge need to be transferred in 15ms? Since the quantity of electricity, Q=It then 𝑄 0.24 Current, 𝐼 = = = 16𝐴 𝑡 15𝑚  Example 8 If a current of 10A flows for four minutes, find the quantity of electricity transferred.  Solution Ex 8 Quantity of electricity, Q=It coulombs. I =10A and t =4×60=240 s Hence; 𝑄 = 10 × 240 = 2400 𝐶 Potential Difference, V The difference of potential between two points of a conducting wire. Symbol: V Unit : Volt (V) Resistance, R It is a measure of the opposition to the flow of charge through a load. Symbol: R Unit : Ohm () Conductor It is a material with low resistance which allows electric current to flow in it, as it has masses of free electrons e.g. copper, aluminum, silver, platinum, bronze, gold, etc. Main Effect of Electric Circuit 1. Heat 2. Magnetic 3. Chemical  Heat Effect When electric current flows through a wire, the wire gets heated Example: soldering iron, water heater, fuse, bulb, cookers, boilers, kettles, iron  Magnetic Effect When electric current flows through a wire, it behaves like a magnet. Example: bells, relays, motors, generators, transformers, telephones, lifting magnets, car ignition  Chemical Effect The passage of an electric current through a conducting liquid causes chemical reactions. Example: cell and battery, electroplating Resistance and resistivity Resistance & resistivity ❖Resistance – property of a component which restricts the flow of electric current. ❖4 factors that influence the value of resistance 1. Length of the conductor, l 2. Cross-sectional area of the conductor, A 3. Resistivity, ρ 4. Temparature of material  Length of conductor, Resistance is proportional to the length of wire. Longer wire resulting high resistance in a load. R Cross Sectional Area, A Resistance is inversely proportional to cross sectional area of wire. 1 R A Resistivity , It is a constant for a material relating its resistance to its length and cross-sectional area. Resistance is proportional to resistivity. R  Temperature, T For moderate range of temperature, such as 100ºC, the change of resistance is proportional to the change of temperature. RT  Equation: ρl R= [Unit = Ω] 𝐴 R = resistance [Ω] l =Length [m] A = Cross-sectional area [m2] ρ = resistivity [Ω.m] Resistivity is difference for different material  Example 9 Example 1.7 Calculate resistance of a 5m long conductor if it has cross sectional area 10𝑚𝑚2 and resistivity 0.3 𝑥 10−5 Ω.m 𝜌𝑙 0.3 x 10−5 x 5 Resistance, R= = A 10 x 10−6 = 1.5Ω  Example 10 Calculate the resistance of a 3 km length of aluminium overhead power cable if the cross-sectional area of the cable is 10 mm2. Take the resistivity of aluminium to be 0.03 x 10-6 Ωm.  Solution Ex 10 Length,l = 3 km = 3000m Cross-sectional area,A = 10 mm2 = 10 mm x 1 mm = 0.01 x 0.001m = 10 x 10-6m2 Resistivity, 𝜌 = 0.03 x 10-6Ωm Then 𝜌𝑙 0.03 × 10−6 3000 𝑅= = −6 = 9Ω 𝐴 10 × 10 Resistor (R) A device that is manufactured to have specific resistance. Used to limit current flow and reduce voltage applied to other components. Basic unit is ohm (Ω)  SELF-EXERCISE i) In what time would a current of 1 A transfer a charge of 30 C? ANSWER30s Answer: ii) What would be the resistivity of 2m length conductor wire if the resistance value is 500Ω and the cross-sectional area 0.5𝑚𝑚2 Answer: 125µΩm ANSWER https://padlet.com/carolineannmai/7wbysdrbbhgaf22t