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1 Hands-On, Minds-On, Hearts-On Intrusion and Access Control Security Technology Department Chapter 1 Fundamentals in electrical measurements

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2 2Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Objectives 1.State the factors affecting the resistance of a resistor and perform resistance calculation. 2.Explain basic electrical units of measurements. 3.Compute electrical parameters using Ohm’s law.

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3 3Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Electrical Fundamentals Watch the video from: http://www.youtube.com/watch?v=dDIy-tLy4Ts http://www.youtube.com/watch?v=dDIy-tLy4Ts Torture flies (electric circuit)

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4 4Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Voltage (V) source of potential energy also called electromotive force (or EMF) energy can be obtained from: a battery power supply solar cell generator Units: Volts (V).

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5 5Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Simple Electric Circuit

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6 6Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Current If voltage is applied across conductive or semi conductive material, one end becomes +ve, the other end is –ve. Results in movement electrons Symbol : I, Unit: ampere (A)

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7 7Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Resistance Opposition that restricts the flow of current. Symbol : R Unit : Ohm (Ω)

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8 8Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Schematic Symbols Voltage Source Resistor Conductor

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9 9Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Ohm’s Law States that the ratio of potential difference (V) between any two points on a load to the current (I) flowing between them is constant provided the temperature of the load does not change. R is the resistance of the load between the two points considered

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10 Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Example 1 A heater with a resistance of 8 is connected across the 120 V power line. Find the current flowing through the heater. I = V/R I = 120V/8 =15A 10

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11 Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Example 2 How many amperes of currents are flowing in the circuit? I 100V 25

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12 Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Example 3 A current of 5A passes through a circuit having a resistance of 10 . Find the voltage across the circuit.

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13 Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Example 4 An electric circuit is supplied by 12V battery. Calculate the resistance when the current draws out from the battery is 3 amperes.

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14 Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Power in An Electrical Circuit When current flows through resistance, there is a loss of energy resulting in heat. There is always a certain amount of power in an electrical circuit. I V R

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15 Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Power Calculations P = I 2 R = IV = V 2 R Unit: Watts (W)

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16 Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Power Example 1 Calculate the power in the circuit I 10 5V

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17 Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Power Example 2 Calculate the power in the circuit R 2A 10V

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18 Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Power Example 3 Calculate the power in the circuit 2A 50 V

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19 Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Power Example 4 Calculate the supply voltage, current and resistance I 1.5W 50V

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20 Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements FACTORS AFFECTING THE RESISTANCE OF RESISTORS At constant temperature, the resistance of a conductor is determined by 3 factors a)length of conductor b)Cross-sectional area ( A ) of the conductor c)material used. is known as its specific resistance or resistivity Resistance,

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21 Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Example 1 Calculate the length of a 1.5 mm diameter copper wire, having a resistance of 0.3 ohm and that the resistivity of copper is 0.017 µΩ-m.

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22 Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Example 2 Calculate the resistance of 100m length of copper wire having a cross-sectional area of 0.1 mm 2 if its resistivity is 50 x 10 -8 ohm-cm. (Answer: 5 )

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