Ee study notes
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EE Study Notes provides information on various electrical engineering concepts: 1. Ohm's Law defines the relationship between voltage, current, and resistance in a circuit. Resistors in series have a total voltage equal to the sum of individual voltages and a single current. Resistors in parallel have the same voltage but total current equals the sum of individual currents. 2. Capacitors store energy in the form of electric charge, with capacitance determining how much charge is stored for a given voltage. Capacitors combine in series and parallel like resistors. 3. AC circuits have voltage and current that vary sinusoidally over time. Phase relationships describe whether voltage and current are in phase, or if
Ee study notes
- 1. EE Study Notes Ohm’s Law V = IR where V is Voltage, I is current and R is resistance Current and Resistance aredirectly proportional to voltage. i.e. if current/resistance increase, voltage also increases Current is inversely proportional to resistance. i.e. If current increase, resistance decrease and vice versa Resistors in Series Total voltage = sum of voltage across all resistors in series. Vt= V1 +V2 + V3 Total resistance = sum of all resistors in circuit. i.e. Rt = R1 + R2 + R3 + ….. The current through all the resistors is the same. Resistors in Parallel Voltage across all resistors in a parallel circuit is the same. V = V1 = V2 = V3 Total current = sum of all current travelling through each resistor Total resistance:
- 2. Power, Energy & Efficiency Unit of Charge: Coulomb (Q) Unit of Energy : Joules (J) or kWh (kilowatt-hours) Unit of Power : Watts or J/s (W) Energy = I2Rt joules = Power x Time Power = Voltage x Current P=IV The totalpower for both seriesand parallel circuits, is equal to the sum of the powers in each resistor : PT = P1 + P2 + P3 + … … + Pn Efficiency: Cells Types of cells o Wet Leclanche Cell o Dry Leclanche Cell o Mercury Cell o Carbon-Zinc Dry Cell o Alkaline-Manganese Cell Internal Resistance V = E – Ir V = IR where V = terminal voltage of cell E = open circuit voltage of cell r = internal resistance of cell R = load resistance I = load current
- 3. The emf (E) of a cell is the total voltage generated by the cell is measured with the cell open-circuit (also called open circuit voltage of cell). The terminal voltage, or potential difference (p.d.) of a cell, is the voltage across the cell terminals when the cell is supplying current to a load Capacitors A capacitor is a device which stores energy in the form of electric charge. Symbol : C, Unit: Farad (F) Capacitance = Charge / Voltage The larger the capacitance, the larger will be the charge stored. Capacitance (C) is directly proportional to the dielectric permittivity( ). Capacitors in Parallel & Series In series: 1 1 1 1 CT C1 C2 C3
- 4. In Parallel: CT = C1 + C2 + C3 + ... ...+ Cn AC Circuits Period - The time required for a given sine wave to complete one full cycle. o symbol - T o unit - second (s) Period Measurement - From one zero crossing to the corresponding zero crossing in the next cycle Frequency - The number of cycles a sine wave can complete in 1 second. o symbol : f o unit - Hertz (Hz) Frequency vs Period If an ac voltage is applied to a circuit, an ac current flows.The voltage and current will have the same frequency. Ways to express and measure the value of a sine wave : o instantaneous value. o peak value. o peak-to-peak value. o root-mean-square value. o average value.
- 5. Peak Value - The voltage or current value of a waveform at its maximum positive or negative points. o Vpor Vmax o Ip or Imax Peak-to-Peak: The voltage or current value of a waveform measured from its minimum to its maximum points. o Vpp or Ipp o Vpp = 2 x Vmax or Vmax = 0.5 x Vpp Root Mean Square Value o Vrms= 0.707 x Vmax Average Value o Vavg= 0.637 x Vmax Phasor Diagram There are three ways to describe the phase angle in a phasor diagram: 1. Same phase or in phase 2. Leading 3. Lagging Characteristics of A.C. Pure Resistive Circuit o Voltage and current are equally opposed by the circuit. o The current(I) flows through the resistor is in-phase with the applied voltage(V). o The phase angle between the applied voltage and current is 0° V I = ---- R Characteristics of A.C. Pure Inductive Circuit o There is opposition to current flow. o Current flows through the pure inductor lags the applied voltage by 90°. o The phase angle between the applied voltage and current is 90°. ( = 90° ) XL = 2 f L XL: inductive reactance( ), f: Frequency(Hz), L: Inductance(H)
- 6. Characteristics of A.C. Pure Capacitive Circuit o Current flows through the pure capacitor leads the applied voltage by 90°. o The phase angle between the applied voltage and current is 90°. ( = 90° ) 1 Xc = --------- 2 fC Xc: Capacitive reactance( ), f: Frequency(Hz), C: Capacitance(F) Impedence Characteristics of A.C. RL Series Circuit o Current is in phase with VR. o Current lags VL by 90o. o Current lags VS by where is the phase angle or phase difference. Impedence: The opposition to the current flow is called the impedance. o Symbol : Z o Unit : Ohms ( ) Formulae: o Vs = IZ where Vs = supply voltage, I = current, and Z = impedence o where Z = impedence, R = Resistance, and XL= inductive reactance Characteristics of A.C. RC Series Circuit o Current is in phase with VR. o Current leads VC by 90o. o Current leads VS by where is the phase angle or phase difference. Formulae: o Vs = IZ where Vs = supply voltage, I = current, and Z = impedence o where Z = impedence, R = Resistance, and Xc= capacitive reactance