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

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.

3 3Prepared by Sandy Tay Chapter 1 – Fundamentals in electrical measurements Electrical Fundamentals Watch the video from:  Torture flies (electric circuit)

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).

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

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)

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

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

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

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

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 

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.

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.

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

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

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

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

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

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

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,

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 µΩ-m.

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 ohm-cm. (Answer: 5  )