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BASICS OF ELECTRICAL CIRCUIT

• An electric circuit consists of electrical elements connected together.

• The International System of Units (SI) is the international measurement language, which enables engineers to communicate their results. From the six principal units, the units of other physical quantities can be derived.

Definition of TermsCharge is an electrical property of the atomic

particles of which matter consists, measured in coulombs (C). Each electron has -1.602 x 10-19 C

Electric current is the time rate of change of charge, measured in amperes (A).

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Definition of Terms

A direct current (dc) is a current that remains constant with time.

An alternating current (ac) is a current that varies sinusoidally with time.

Voltage (or potential difference) is the energy required to move a unit charge through an element, measured in volts (V).

Definition of TermsPower is the time rate of expending or

absorbing energy, measured in watts (W). Note: 1 Hp = 746 W

Passive sign convention is satisfied when the current enters through the positive terminal of an element and P = +VI. If the current enters through the negative terminal, P = -VI.

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Definition of Terms

Energy is the capacity to do work, measured in Joules (J). Note: 1 Wh = 3.6 kJ

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Definition of Terms

An ideal independent source is an active element that provides a specified voltage or current that is completely independent of other circuit elements.

An ideal dependent (or controlled) source is an active element in which the source quantity is controlled by another voltage or current.

Definition of Terms

An ideal independent source is an active element that provides a specified voltage or current that is completely independent of other circuit elements.

An ideal dependent (or controlled) source is an active element in which the source quantity is controlled by another voltage or current.

EXERCISE

#1

How much charge is represented by 4,600 electrons?

#2The total charge entering a terminal is given by

q = 5tsin(4πt) mC. Calculate the current at t = 500 ms.

#3Determine the total charge entering a terminal

between t = 1 s and t = 2 s if the current passing the terminal is i = (3t2 – t) A.

#4An energy source forces a constant current of 2 A for 10

s to flow through a light bulb. If 2.3 kJ is given off in the form of light and heat energy, calculate the voltage drop across the bulb.

#5Find the power delivered to an element at t = 3 ms if the current entering its positive terminal is i = 5cos(60πt) A and the voltage is v = 3i.

#6

How much energy in kJ does a 100-W electric bulb consume in two hours?

#7Calculate the power supplied or absorbed by

each element in the circuit.

#8

A homeowner consumes 700 kWh in January. Determine the electricity bill for the month using the following residential rate schedule:Base monthly charge of $12.00.First 100 kWh per month at 16 cents/kWh.Next 200 kWh per month at 10 cents/kWh.Over 300 kWh per month at 6 cents/kWh.

#9The charge entering a certain element is shown

in the graph. Determine the current at t = 6ms.

#10The charge flowing in a wire is plotted. Sketch

the corresponding current.

#11A rechargeable flashlight battery is capable of

delivering 85 mA for about 12 h. How much charge can it release at that rate? If its terminal voltage is 1.2 V, how much energy can the battery deliver?

#12The current entering the positive terminal of a

device is i(t) = 3e-2t A and the voltage across the device is v(t) = 5di/dt V. (a) Determine the charge delivered to the device between t = 0 s and t = 2 s. (b) Calculate the power absorbed. (c) Determine the energy absorbed in 3 s.

Electricity in our Daily Lives

• Check the power ratings of your appliances at home

• Check how MERALCO computes your electrical bill.