Basic Electricity
• What is Current?
The flow of electrons in a circuit is called current, it is measured in Amperes (I).
• What is Voltage?
Voltage is the difference in potential (charge) between two points or voltage is the
amount of driving force or pressure applied to a circuit, it is measured in Volts (V).
• What is Resistance?
The resistance of a circuit is the circuit's opposition to the movement of electrons. A
resistor restricts or limits the amount of current flowing in a electrical circuit, it is
measured in Ohm (Ω).
Series Resistor: When resistors are connected in series they have one point in
common. The total resistance is equal to the sum of the individual resistors.
R tot = R1 + R2 + R3
The current in a series circuit is the same in each component of the circuit because
the current must flow through each resistor in series to get to the next resistor.
I tot = I1 = I2 = I3
The applied voltage divides across each component in a circuit in proportion to the
resistance of the component. V tot = V1 + V2 + V3
Parallel Resistor: When resistors are connected in parallel, they have two points in
common. The total resistance of parallel resistors is equal to the reciprocal of the
sum of the reciprocal of the individual resistors. R tot of a parallel circuit is called the
equivalent resistance,
R eq = 1/1/R1+ 1/R2+1/R3
• Why color-coding is necessary for resistor?
A wide variety of resistors are physically large enough to have their resistance value
printed on them. However, carbon composition resistors are too small for this
method of identification so a color coding system is used. Four bands are printed on
one end of the resistor and are read from the band closest to the end of the resistor
toward the center. Each color represents a numerical value as indicated below.
0- Black 3- Orange 6- Blue 9- White ±5% - Gold } Tolerance
1- Brown 4- Yellow 7- Violet 0.1- Gold ±10% - Silver }
2- Red 5- Green 8- Grey 0.01- Silver
Suppose the color bands of a resistor are yellow, violet, red and gold. The resistance
value is determined as follows:
4 7 00 = 4700Ω
Yellow = 4
Violet = 7
Red = 2 (two zeros)
Gold = ±5%
4700+5% = 4935} The actual resistance should be between 4467 and 4935 ohms.
4700-5% = 4465}
Occasionally a fifth band is used to indicate the failure rate of the resistor:
Yellow 0.001% per 1000 hours
Orange 0.01% per 1000 hours
Red 0.1% per 1000 hours
Brown 1.0% per 1000 hours
• What does Ohm's Law states?
In a closed electrical circuit, current is directly proportional to voltage and inversely
proportional to resistance at constant temperature.
I= V/R. Where I= Current, V= Voltage & R= Resistance
• What does Kirchhoff's voltage law states?
Kirchhoff's voltage law states that " the algebraic sum of potential rises and drops
around a closed loop is zero." ΣV= 0
• What does Kirchhoff's current law states?
Kirchhoff's current law states that " the algebraic sum of current entering and leaving
a node is zero." (A node is a junction of two or more branches.)
• What is a Capacitor?
When two conductors are placed side by side, separated by a nonconductive
material, and connected across a battery, free electrons drift in the direction of the
driving voltage is called capacitor. Its unit is farad, normally in micro farad (μf) or
Pico farad (pf).
• What is Inductor?
Inductors use the ability of electrical current to create a magnetic field. If a voltage is
applied to a coil of wire, the current flowing in the coil will cause a magnetic field to
develop. The more times the wire is coiled and the more current there is in the coil,
the greater the strength of the magnetic field. Its unit is Henry, normally in milli
Henry (mH).
• What is Inductance?
The property of a coil that opposes a change in the current flow is called inductance.
The inductance of a coil depends on four factors:
1) The number of turns (windings) in the coil. Inductance is proportional to the
square of the number of turns in the coil.
2) The diameter of the coil. The larger the diameter of the coil, the higher the
inductance.
3) The permeability (ability to become magnetized) of the core material.
4) The length of the coil. The shorter the coil, the higher the inductance.
• What is Power?
Power is a rate of doing work, or works done per unit in time. The unit for measuring
power is the Watt (W). Power in watts is equal to the product of the applied voltage
and the current flowing. Stated algebraically, P = I E
• What is Alternating Current?
Continually changing amount and direction of the current and voltage is called
alternating current (AC). The components of an ac circuit causes a time period to be
introduced between current and voltage; that is, current and voltage are out of phase.
Few definitions and symbols used in alternating current
1) Amplitude or peak value: The maximum value reached by a waveform.
2) Capacitive reactance (XC): measured in ohms, is the opposition to a change in
current flow provided by a capacitor. Capacitive reactance causes current to lead
voltage by 90°: Xc = 1/2p f C.
3) Cycle: The portion of a waveform contained in one period of time.
4) Effective value: The value of voltage that occurs at 45° (0.7071 times the
maximum value).
5) Frequency: The number of cycles per second is called frequency and measured in
Hertz (Hz).
6) Impedance (Z): The opposition to current flow in an ac circuit. It is a combination
of resistance, Inductance and capacitance.
7) Inductive Reactance (XL): Inductive reactance, measured in ohms, is the
opposition to a change in current flow produced by a coil of wire. Inductive
reactance causes current to lag voltage by 90° : XL = 1/2π f L.
8) Instantaneous value: The magnitude of a waveform at any instant of time.
9) Period (T): The time interval between successive repetitions of a periodic
waveform.
10) Periodic waveform: A waveform that continually repeats itself after the same
time interval.
11) Resistance: the opposition of a circuit to the movement of electrons. Resistance
in an ac circuit acts the same as resistance in dc circuit.
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• What is Current?
The flow of electrons in a circuit is called current, it is measured in Amperes (I).
• What is Voltage?
Voltage is the difference in potential (charge) between two points or voltage is the
amount of driving force or pressure applied to a circuit, it is measured in Volts (V).
• What is Resistance?
The resistance of a circuit is the circuit's opposition to the movement of electrons. A
resistor restricts or limits the amount of current flowing in a electrical circuit, it is
measured in Ohm (Ω).
Series Resistor: When resistors are connected in series they have one point in
common. The total resistance is equal to the sum of the individual resistors.
R tot = R1 + R2 + R3
The current in a series circuit is the same in each component of the circuit because
the current must flow through each resistor in series to get to the next resistor.
I tot = I1 = I2 = I3
The applied voltage divides across each component in a circuit in proportion to the
resistance of the component. V tot = V1 + V2 + V3
Parallel Resistor: When resistors are connected in parallel, they have two points in
common. The total resistance of parallel resistors is equal to the reciprocal of the
sum of the reciprocal of the individual resistors. R tot of a parallel circuit is called the
equivalent resistance,
R eq = 1/1/R1+ 1/R2+1/R3
• Why color-coding is necessary for resistor?
A wide variety of resistors are physically large enough to have their resistance value
printed on them. However, carbon composition resistors are too small for this
method of identification so a color coding system is used. Four bands are printed on
one end of the resistor and are read from the band closest to the end of the resistor
toward the center. Each color represents a numerical value as indicated below.
0- Black 3- Orange 6- Blue 9- White ±5% - Gold } Tolerance
1- Brown 4- Yellow 7- Violet 0.1- Gold ±10% - Silver }
2- Red 5- Green 8- Grey 0.01- Silver
Suppose the color bands of a resistor are yellow, violet, red and gold. The resistance
value is determined as follows:
4 7 00 = 4700Ω
Yellow = 4
Violet = 7
Red = 2 (two zeros)
Gold = ±5%
4700+5% = 4935} The actual resistance should be between 4467 and 4935 ohms.
4700-5% = 4465}
Occasionally a fifth band is used to indicate the failure rate of the resistor:
Yellow 0.001% per 1000 hours
Orange 0.01% per 1000 hours
Red 0.1% per 1000 hours
Brown 1.0% per 1000 hours
• What does Ohm's Law states?
In a closed electrical circuit, current is directly proportional to voltage and inversely
proportional to resistance at constant temperature.
I= V/R. Where I= Current, V= Voltage & R= Resistance
• What does Kirchhoff's voltage law states?
Kirchhoff's voltage law states that " the algebraic sum of potential rises and drops
around a closed loop is zero." ΣV= 0
• What does Kirchhoff's current law states?
Kirchhoff's current law states that " the algebraic sum of current entering and leaving
a node is zero." (A node is a junction of two or more branches.)
• What is a Capacitor?
When two conductors are placed side by side, separated by a nonconductive
material, and connected across a battery, free electrons drift in the direction of the
driving voltage is called capacitor. Its unit is farad, normally in micro farad (μf) or
Pico farad (pf).
• What is Inductor?
Inductors use the ability of electrical current to create a magnetic field. If a voltage is
applied to a coil of wire, the current flowing in the coil will cause a magnetic field to
develop. The more times the wire is coiled and the more current there is in the coil,
the greater the strength of the magnetic field. Its unit is Henry, normally in milli
Henry (mH).
• What is Inductance?
The property of a coil that opposes a change in the current flow is called inductance.
The inductance of a coil depends on four factors:
1) The number of turns (windings) in the coil. Inductance is proportional to the
square of the number of turns in the coil.
2) The diameter of the coil. The larger the diameter of the coil, the higher the
inductance.
3) The permeability (ability to become magnetized) of the core material.
4) The length of the coil. The shorter the coil, the higher the inductance.
• What is Power?
Power is a rate of doing work, or works done per unit in time. The unit for measuring
power is the Watt (W). Power in watts is equal to the product of the applied voltage
and the current flowing. Stated algebraically, P = I E
• What is Alternating Current?
Continually changing amount and direction of the current and voltage is called
alternating current (AC). The components of an ac circuit causes a time period to be
introduced between current and voltage; that is, current and voltage are out of phase.
Few definitions and symbols used in alternating current
1) Amplitude or peak value: The maximum value reached by a waveform.
2) Capacitive reactance (XC): measured in ohms, is the opposition to a change in
current flow provided by a capacitor. Capacitive reactance causes current to lead
voltage by 90°: Xc = 1/2p f C.
3) Cycle: The portion of a waveform contained in one period of time.
4) Effective value: The value of voltage that occurs at 45° (0.7071 times the
maximum value).
5) Frequency: The number of cycles per second is called frequency and measured in
Hertz (Hz).
6) Impedance (Z): The opposition to current flow in an ac circuit. It is a combination
of resistance, Inductance and capacitance.
7) Inductive Reactance (XL): Inductive reactance, measured in ohms, is the
opposition to a change in current flow produced by a coil of wire. Inductive
reactance causes current to lag voltage by 90° : XL = 1/2π f L.
8) Instantaneous value: The magnitude of a waveform at any instant of time.
9) Period (T): The time interval between successive repetitions of a periodic
waveform.
10) Periodic waveform: A waveform that continually repeats itself after the same
time interval.
11) Resistance: the opposition of a circuit to the movement of electrons. Resistance
in an ac circuit acts the same as resistance in dc circuit.
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