SET Chapter 3.pdf

Learning Outcomes Understand the relationship between voltage, current and resistance (Ohm’s law): V=I ×R Apply Ohm’s law to determine voltage, current or resistance in an electric circuit Connect a simple electric circuit comprising a voltmeter, an ammeter, a load and a power supply...

Learning Outcomes Understand the relationship between voltage, current and resistance (Ohm’s law): V=I ×R Apply Ohm’s law to determine voltage, current or resistance in an electric circuit Connect a simple electric circuit comprising a voltmeter, an ammeter, a load and a power supply to verify Ohm’s law 1.3.1 Ohm’s Discovery The relationship between V, I and R was discovered by scientist, Georg Simon Ohm. This discovery, known as Ohm’s law, is the basic formula used in all electric circuits. Ohm’s law states that the current (I ) flowing through a conductor is directly proportional to the potential difference (V ) applied across its ends, provided the temperature remains constant. ↳ voltage/EMF (Voltage increase current , increase) Fig. 1.3-1: Simple electric circuit The following formula is derived from Ohm’s law: V=I×R I = = where V is voltage in volts (V) I is current in amperes (A) R R is resistance in ohms (Ω) Unit 1.3 | Electric Circuit Laws 10  1.3.2 Worked Examples Fig. 1.3-2: Simple electric circuit (a) Refer to Fig. 1.3-2, determine V if I = 0.5 A and R = 20 Ω. V=I ×R = 0.5 A × 20 Ω = 10 V (b) A load of resistance 500 Ω is connected to a supply of 230 V. What is the current drawn from the supply? V V I = R - 230 V F = 500 Ω = 0.46 A Notes ! M : micro -100 000 louA 100000 = = 0. 001A M : willi = 1000 Int = += 0 005A. kilo +1000 20km = 20x1000 20000 - = k : M : Mega x 100000 0 3 MV. = 0 3 +100000. = 30000 Unit 1.3 | Electric Circuit Laws 11  1.3.3 Practice Questions ⑮D V = [xR V I = it I R R = Fig. 1.3-3: Simple electric circuit (a) Referring to Fig. 1.3-3, determine: (i) V if I = 0.5 A and R = 100 Ω. [50 V] V = IXR = 0. 5/ x100m = (ii) I if V = 110 V and R = 550 Ω. [0.2 A] I (iii) R if V = 230 V and I = 1.2 A. [191.67 Ω] V R = I = 4x1000 (iv) I if V = 24 V and R = 10 kΩ (kilo-ohms). [0.0024 A] = =1 ↳ convert to otims I = 0 0024A.. R = 10ke I = 10 X 1000 - 10000 = 100002 (b) A load with resistance of 200 Ω is connected to a supply of 110 V. What is the current drawn from the supply? R 2001 V [0.55 A] llOV I =? =. =. I - (c) The current flowing in a circuit with a load of resistance 50 Ω is 0.2 A. What is the supply voltage? [10 V] R = 50r I 0. =. 2A V IXR = 50x0 2 V ? = =. ↓V. I Unit 1.3 | Electric Circuit Laws 12