Basics of Electricity and Circuits

Basics of Electricity

Definition of Electric Current

  • Current is defined as the rate of flow of charge.

  • Symbol for Current: I

  • Unit for Current: ampere (A)

  • Formula to Calculate Current:

    • I = \frac{q}{t}

    • Where:

    • I = current

    • q = charge

    • t = time

  • Apparatus Used: ammeter

Definition of Voltage

  • Voltage is the electric potential difference in the circuit.

  • Symbol for Voltage: V

  • Unit for Voltage: volts (V)

  • Fundamental Relation for Voltage:

    • V = I \times R

    • Where:

    • I = current

    • R = resistance

  • Apparatus Used: voltmeter

  • Connection of Voltmeters: Voltmeters are connected to a circuit in parallel.

  • Alternative Formula for Voltage:

    • V = \frac{E}{q}

    • Where:

    • E = energy

    • q = charge

Categories of Voltage

Potential Difference (PD)

  • Refers to the energy required to carry charge between two points in a circuit.

  • Measured across components, e.g., a light bulb.

Electromotive Force (EMF)

  • Refers to the energy required to carry charge around the entire circuit.

  • Supplied by the source of power, e.g., battery or cell.

  • Important distinction: EMF is the total energy provided, while PD is energy used between two specific points.

Definition of Resistance

  • Resistance is defined as the opposition to current.

  • Symbol for Resistance: R

  • Unit for Resistance: ohm (Ω)

  • Measurement Devices: Measured with a fixed resistor or a variable resistor.

Examples of Resistors

  • Light bulb

  • Diode or LED

  • Thermistor

Factors Affecting Resistance

Temperature

  • When temperature increases, resistance also increases.

  • Explanation using metaphor:

    • Imagine 10 blind people running versus walking in a closed room.

    • Running individuals would more likely bump into one another, indicating higher resistance at elevated temperatures.

Length

  • As length of the conductor increases, the distance the charges travel becomes longer.

  • Result: Resistance increases.

Thickness

  • The thickness of the wire affects resistance.

  • Thicker wires allow more charge to flow and thus lead to decreased resistance.

  • General rule: As thickness increases, resistance decreases.

Comparison of Circuit Types

Series Circuits

  • Current throughout a series circuit remains constant.

    • I1 = I 2

  • Voltage splits across components.

    • Total Voltage:

    • V{total} = V1 + V2

  • Total Resistance in Series:

    • R{total} = R1 + R2

  • Example Calculation:

    • If R1 = 3Ω and R2 = 3Ω, then

    • Total Resistance = 6Ω

  • Advantages of Series Circuits:

    • Simpler design.

    • No overheating issues.

    • Batteries last longer as current is less drawn.

  • Disadvantages of Series Circuits:

    • If one component fails (e.g., a bulb), the entire circuit stops working.

    • Individual control of components is not possible.

Parallel Circuits

  • Current splits in a parallel circuit.

    • Total Current:

    • I{total} = I1 + I2

  • Voltage remains the same across each branch.

    • Total Voltage:

    • V{total} = V1 = V2

  • Total Resistance in Parallel:

    • 1/Rtotal = 1/R1 + 1/R2

  • Example Calculation:

    • For R1 = 3Ω and R2 = 3Ω

    • Total resistance \frac{1}{R_{total}} = \frac{1}{3} + \frac{1}{3} = \frac{2}{3}

    • Therefore, total resistance R_{total} = \frac{3}{2}Ω = 1.5Ω

  • Advantages of Parallel Circuits:

    • Individual control of components.

    • If one component fails, others continue to work.

    • Fulfillment of higher brightness for lamps.

  • Disadvantages of Parallel Circuits:

    • More complex circuit design.

    • Can overheat under certain conditions.

    • Batteries may drain faster due to higher total current draw.