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- 1.1 Systems of Units.
- 1.2 Electric Charge.
- 1.3 Current.
- 1.4 Voltage.
- 1.5 Power and Energy.
- 1.6 Circuit Elements.
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4
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5
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- Charge is an electrical property of the atomic particles of which matter
consists, measured in coulombs (C).
- The charge e on one electron is negative and equal in magnitude to 1.602
´ 10-19 C which
is called as electronic charge. The charges that occur in nature are integral
multiples of the electronic charge.
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- Electric current i = dq/dt. The unit of ampere can be derived as 1 A =
1C/s.
- A direct current (dc) is a current that remains constant with time.
- An alternating current (ac) is a current that varies sinusoidally with
time. (reverse direction)
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- The direction of current flow
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- Example 1
- A conductor has a constant current of
5 A.
- How many electrons pass a fixed point on the conductor in one minute?
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- Solution
- Total no. of charges pass in 1 min is given by
- 5 A = (5 C/s)(60 s/min) = 300 C/min
- Total no. of electronics pass in 1 min is given
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- Voltage (or potential difference) is the energy required to move a unit
charge through an element, measured in volts (V).
- Mathematically,
(volt)
- w is energy in joules (J) and q is charge in coulomb (C).
- Electric voltage, vab, is always across the circuit element
or between two points in a circuit.
- vab > 0 means the potential of a is higher than potential
of b.
- vab < 0 means the potential of a is lower than
potential of b.
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- Power is the time rate of expending or absorbing energy, measured in
watts (W).
- Mathematical expression:
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- The law of conservation of energy
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13
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14
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15
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Notes