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CHAPTER 1 : INTRODUCTION TO ELECTRICAL CIRCUITS

CHAPTER 1 : INTRODUCTION TO ELECTRICAL CIRCUITS. 1.1 ELECTRICAL QUANTITIES. Electromagnetic Force (EMF) Emf provided by a source of energy such as a battery or a generator Symbol - E Unit - Volt (V) Electrical Charge Has two types, positive charge and negative charne Symbol - Q

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CHAPTER 1 : INTRODUCTION TO ELECTRICAL CIRCUITS

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  1. CHAPTER 1 : INTRODUCTION TO ELECTRICAL CIRCUITS

  2. 1.1 ELECTRICAL QUANTITIES • Electromagnetic Force (EMF) • Emf provided by a source of energy such as a battery or a generator • Symbol - E • Unit - Volt (V) • Electrical Charge • Has two types, positive charge and negative charne • Symbol - Q • Unit - Coulomb (C) • Electric field of positive and negative charge

  3. Current • Is a flow of electrical charge through a conductive medium • Symbol - I • Unit - Ampere (A) • Electrical Potential • A change in electrical potential between two points in an electrical circuit is called potential difference • Symbol - V • Unit - Volt (V)

  4. Resistance • the opposition to the passage of an electrical current through that element • Symbol - R • Unit - Ohm (Ω) • Conductor • is a material which contains movable electric charge • such as copper or aluminium • the movable charged particles are electrons • Insulator • is a material whose internal electric charges do not flow freely • such as glass, paper

  5. 1.1.1 Factors that effect the resistance of conductor material • Resistivity (ρ) - is a measure of how strongly a material opposes the flow of electric current R ρ • Length (ℓ) – length of the wire R ℓ • Cross Sectional Area (A) – cross sectional area of the wire R • Temperature (T) R T

  6. factors can be represented in the form of the equation below: Where as: R = resistance (Ω) = resistivity (Ωm) = length (m) A = cross sectional () • E.g Calculate the resistance of aluminium wire of length 1.5km. Given wire diameter is 10mm and the resistivity is 0.025 μΩm

  7. 1.2 Types of electrical circuit • Complete Circuit • connection is closed and allows current to flow properly • Open Circuit • loads in the circuit is open • Short Circuit • The load is short circuit using conductor

  8. 1.2.1 Use of meters • Voltmeter - instrument used for measuring electrical potential difference between two points in an electric circuit • Ammeter - is a measuring instrument used to measure the electric current in a circuit • Ohmmeter - is an electrical instrument that measures electrical resistance

  9. 1.3 Ohm’s Law • states that the current (I) is proportional to the potential difference (V) and inversely proportional to the resistance (R). Where: I = current (A) V = voltage (V) R = resistance (R)

  10. E.g 1 Determine the current resulting from the application of a 9V battery across the network with a resistance of 2.2Ω • E.g 2 Calculate the voltage that must be applied across the soldering iron to establish a current of 1.5A through the iron if its internal resistance is 80Ω.

  11. 1.4 Electrical Power • Is an indication of how much work can be accomplished in a specified amount of time. Where P = power (Watt) W = Work (Joule) t = time (second) • Derive from ohm’s law formula: Where I = current (A) V = voltage (V)

  12. 1.4.1 Use of Wattmeter

  13. Example • E.g 1 An electric heater works on 120V and draws 3A of current. How much power does it use? • E.g 2 What is the power when there are 500mA of a current through at 4.7kΩ resistor. • E.g 3 If a 75V source is supplying 2A to a load, what is the resistance value of the load.

  14. 1.5 Electrical Energy • Is the ability to do work and power is the rate at which energy is used Where E = Energy (kWj/ Joule) P = Power (W) t = time (s)

  15. 1.5.1Use of kilowatt-hour meter • f

  16. 1.5.2 Relationship between electrical energy and heat energy

  17. 1.5.3 Convertion • Joule – Watt second • Kilowatt hour – Joule • Joule - Calorie

  18. Example • A particular electronic device uses 100 mW power. If it runs for 24 hours. How many joules of energy does it consume? • For how many seconds must there be 5 A of current through a 47 Ω resistor in order to consume 25 J • A 12V source is connected across a 10 Ω resistor • How much energy is used in two minutes? • If the resistor is disconnected after one minute, is the power during the first minute greater than, less than or equal to the power during a two minute interval

  19. 1.6 Series and Parallel Circuit 1.6.1 Series Circuit • + • = • + CSVD = CURRENT SAME VOLTAGE DIFFERENT

  20. Example • Three 470 Ω resistors are connected in series with a 48V source. • Four equal value resistor are in series with a 5V battery, and 2.23mA are measured. What is the value of each resistor.

  21. 1.6.2 Parallel Circuit • + • = VSCD = VOLTAGE SAME CURRENT DIFFERENT

  22. Example

  23. 1.6.3 Voltage Divider Rule

  24. 1.6.4 Current Divider Rule

  25. 1.6.5 Series – Parallel Circuit

  26. 1.7 Kirchoff’s Law 1.7.1 Kirchoff’s Current Law

  27. 1.7.2 Kirchoff’sVoltage Law

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