Introduction to Electricity Notes

Electricity

• Electricity is the movement of electrons.
• It's an invisible force powering light, heat, sound, and motion.

Types of Electrical Power

• Electrical power is mainly transported and consumed in two forms: Alternating Current (AC) and Direct Current (DC).
  • Alternating Current (AC): Electric current that regularly changes direction many times each second.
  • Direct Current (DC): Electric current that flows in one direction.

3 Elements of Electrical Circuits

• Every electrical circuit needs at least three elements to function:
  • A source to supply electrical energy (e.g., a battery).
  • A load to consume electrical energy (e.g., a light bulb).
  • A conductive path to form a continuous path from the source to the load and back to the source (e.g. wires).
• A battery serves as the source of electrical energy
• Electrically conductive wires transport the energy to the light bulb
• The light bulb consumes the energy, converting it into light energy.
• An incandescent light bulb converts electrical energy into light and thermal energy.
• The thermal energy makes the light bulb hot and wastes electrical energy.
• A light-emitting diode (LED) converts electrical energy into light and very few other forms of energy.
• A resistor is sometimes needed with an LED to absorb extra energy and prevent a short circuit due to the LED's efficiency.
• LEDs are more efficient than incandescent light bulbs, leading to widespread adoption in homes.

Circuit Schematic

• A circuit schematic is a graphical model used to represent a circuit design.
• It uses lines for wires and standard symbols for components to represent the circuit's electrical path.

Circuit Configuration

• Components (resistors, batteries, capacitors, etc.) in a circuit can be connected in two ways:
  • Series Circuits: Components are connected end-to-end with only one path for current to flow. If the path is open anywhere, current stops flowing to all components.
  • Parallel Circuits: Both ends of the components are connected together, providing multiple paths for current to flow. If one component is removed, current can still flow to other components through an alternate path.
• Combination Circuits: Contain both series and parallel arrangements.

Electrical Circuit Properties

• An electrical circuit is a system of conductors and components forming a complete path for current to travel.
• Key properties of an electrical circuit include:
  • Voltage: Measured in Volts (V).
  • Current: Measured in Amps (A).
  • Resistance: Measured in Ohms (\Omega).

Current

• Current is the flow of electric charge, measured in Amperes (A).
• Analogy:
  • Tank (Battery)
  • Faucet (Switch)
  • Pipe (Wiring)

Voltage

• Voltage is the force (pressure) that causes current to flow, measured in Volts (V).
• Analogy:
  • Tank (Battery)
  • Faucet (Switch)
  • Pipe (Wiring)

Resistance

• Resistance is the opposition to current flow, measured in Ohms (\Omega).
• Resistors are components that create resistance.
• Reducing current causes the bulb to become dimmer.
• Analogy:
  • Tank (Battery)
  • Faucet (Switch)
  • Pipe (Wiring)

Multimeter

• A multimeter is an instrument used to measure the properties of an electrical circuit, including:
  • Voltage (Volts)
  • Current (Amps)
  • Resistance (Ohms)

Ohm’s Law

• Ohm's Law describes the mathematical relationship between current, voltage, and resistance.
• Quantities, Abbreviations, Units, and Symbols:
  • Voltage (V), Volts (V)
  • Current (I), Amperes (A)
  • Resistance (R), Ohms (\Omega)
• Formulas:
  • V = IR
  • I = V/R
  • R = V/I
• Current in a resistor varies in direct proportion to the voltage applied to it and is inversely proportional to the resistor’s value.

Ohm's Law Chart

• Describes how to calculate Voltage.
• V=IR

Example: Ohm’s Law

• A flashlight uses a 6-volt battery and has a bulb with a resistance of 150 \Omega . How much current will be drawn from the battery when the flashlight is on?
• Schematic Diagram:
  • Given: V_T = 6V, R = 150 \Omega
  • Find: I

Series Circuits

• Characteristics of a series circuit:
  • The current flowing through every series component is equal.
  • The total resistance (RT) is equal to the sum of all the resistances (i.e., R1 + R2 + R3).
  • The sum of all the voltage drops (V{R1} + V{R2} + V{R3}) is equal to the total applied voltage (VT). This is called Kirchhoff’s Voltage Law.

Example: Series Circuit

• For a series circuit, calculate:
  • The total resistance (R_T).
  • The current flowing through each component (IT, I{R1}, I{R2}, & I{R3}).
  • The voltage across each component (VT, V{R1}, V{R2}, & V{R3}).
  • Verify Kirchhoff’s Voltage Law.

Example: Series Circuit Solution

• Given values: R1 = 220 \Omega, R2 = 470 \Omega, R3 = 1.2 k\Omega = 1200 \Omega, VT = 12 V
• Total Resistance:
  • RT = R1 + R2 + R3
  • R_T = 220 \Omega + 470 \Omega + 1200 \Omega
  • R_T = 1890 \Omega
• Current Through Each Component:
  • IT = \frac{VT}{R_T} (Ohm's Law)
  • I_T = \frac{12V}{1890 \Omega} = 0.0063 A = 6.3 mA
  • Since this is a series circuit:
    • IT = I{R1} = I{R2} = I{R3} = 6.3 mA
• Voltage Across Each Component:
  • V = I * R
  • V_{R1} = 0.0063 A * 220 \Omega = 1.386 V
  • V_{R2} = 0.0063 A * 470 \Omega = 2.961 V
  • V_{R3} = 0.0063 A * 1200 \Omega = 7.560 V
• Verify Kirchhoff's Voltage Law:
  • VT = V{R1} + V{R2} + V{R3}
  • 12V = 1.386V + 2.961V + 7.560V
  • 12V \approx 11.907 V

Parallel Circuits

• Characteristics of a Parallel Circuit:
  • The voltage across every parallel component is equal.
  • The total resistance (R_T) is equal to the reciprocal of the sum of the reciprocals:
    • \frac{1}{RT} = \frac{1}{R1} + \frac{1}{R2} + \frac{1}{R3} + …
  • The sum of all of the currents in each branch (I{R1} + I{R2} + I{R3}) is equal to the total current (IT). This is called Kirchhoff’s Current Law.

Example Parallel Circuits

• For the parallel circuit shown, calculate:
  • The total resistance (R_T)
  • The voltage across each component (VT, V{R1}, V{R2}, & V{R3})
  • The current flowing through each component (IT, I{R1}, I{R2}, & I{R3})
  • Use the results to verify Kirchhoff’s Current Law.

Example Parallel Circuits Solution

• Calculate:
  • Total Resistance:
    • \frac{1}{RT} = \frac{1}{R1} + \frac{1}{R2} + \frac{1}{R3}
    • \frac{1}{R_T} = \frac{1}{470 \Omega} + \frac{1}{2200 \Omega} + \frac{1}{3300 \Omega}
    • R_T = 346.59 \Omega \approx 350 \Omega
  • Voltage Across Each Component:
    • Since this is a parallel circuit:
      • VT = V{R1} = V{R2} = V{R3} = 15 \text{ volts}
  • Current Through Each Component
    • I = \frac{V}{R}
    • I{R1} = \frac{V{R1}}{R_1} = \frac{15 V}{470 \Omega} = 0.031915 A \approx 32 mA
    • I{R2} = \frac{V{R2}}{R_2} = \frac{15 V}{2200 \Omega} = 0.006818 A \approx 6.8 mA
    • I{R3} = \frac{V{R3}}{R_3} = \frac{15 V}{3300 \Omega} = 0.004545 A \approx 4.5 mA
    • IT = \frac{VT}{R_T} = \frac{15 V}{346.59 \Omega} = 0.043278 A \approx 43 mA
  • Verify Kirchhoff's Current Law:
    • IT = I{R1} + I{R2} + I{R3}
    • 0.043278 A = 0.031915 A + 0.006818 A + 0.004545 A
    • 0.043278 A \approx 0.043278 A