106 Chapter 6 • Electricity Example 6.10
The power consumption of a resistor is 18 watts when a current of 1,2 amperes flows through it. What is the potential difference across the resistor?
Solution: P = 18 W
I = 1,2 A V = ?
P = VI V = P
I = 18 12, = 15 V
The “power” formula can be expressed in alternative forms bymaking use of Ohm’s law, e.g.:
P = VI watts .................................................................................................... (6.3)
but since: V = IR, P = IR × I, i.e. P = I2R watts ................................................................................................... (6.4)
Example 6.11
An electric kettle is rated at 220 volts, 500 watts. Calculate; (a) (b)
Solution: V = 220 V P = 500 W (a)
P = VI \ I = P V = 500 220 = 2,27 A Example 6.12
Te filament of an incandescent lamp has a resistance of 20 ohms. When connected across a certain supply, it draws a current of 3 amperes. Calculate; (a) (b)
the power consumed by the lamp, and the supply voltage.
(b)
the current that it would draw from the supply, and the resistance of the element.
R = V I = 220 227, = 96,92 ohms
or
P = I2R
\ R = P I2
= 500 2272,
= 97 ohms
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140