Theme 3 Electricity

Ohm's Law

  • Resistance:
      - A property of substances that opposes the movement of electric charges.
      - Responsible for the conversion of electrical energy into another form of energy.
      - Example: The tungsten filament in a light bulb (conversion of electrical energy into thermal energy) and thus transforms into light energy.
      - Measured in ohms (Ω).

  • Conductors and Insulators:
      - In good conductors (like metals), electrons move easily, resulting in low resistance.
      - In poor conductors (like rubber), the movement of charges is resisted, resulting in high resistance.

  • Key Concepts:
      - Current: Movement of electrons.
      - Potential Difference: The energy with which electrons are pushed.
      - Resistance: What opposes the movement of electrons.

Variables in Ohm's Law:

Variable

Unit of Measurement

Symbol

Voltage (tension)

Volt

V

Current

Ampère

I (A)

Resistance

Ohm

R (Ω)

Factors Affecting Resistance:

  1. Length of the Wire:
       - The longer the wire, the higher the resistance.

  2. Diameter of the Wire:
       - The smaller the diameter, the higher the resistance.

  3. Temperature:
       - Lower temperatures result in lower resistance.

  4. Material:
       - The structure of atoms, density of the substance, etc., affect resistance.

Ohmic Resistance:

  • Definition:
      - Devices that always convert the same amount of energy have a constant or ohmic resistance.
      - Example: A lamp in your living room or lights in a classroom emit the same quantity and intensity of light consistently.

  • Resistance Variable:

- dimmer switch

Types of Circuits:

Series Circuits:

  • Definition:
      - There is a single path for the current to flow.
      - All electric charges must pass through each component of the circuit.

  • Characteristics:
      - Adding more charges increases resistance, causing current to decrease.

Advantages:

  • Easy to construct.

  • Economical because they use fewer materials.

Disadvantages:

  • If one charge fails, all other charges in the circuit fail because the circuit becomes open.

  • Adding more charges affects performance since they share the available electrical energy.

Parallel Circuits:

  • Definition:
      - Contains multiple paths for current, allowing each charge to have its own branch in the circuit.

  • Characteristics:
      - Adding more charges does not change resistance; resistance is individual to each branch of the circuit.
      - Current increases as the power supply has to support multiple paths at once.

Advantages:

  • Each charge can be controlled independently from others.

  • Each charge experiences equal voltage (e.g., if the battery provides 3V, each charge will convert 3V; adding more charges in parallel will not diminish the performance of the others).

Disadvantages:

  • More materials are needed to construct, leading to higher costs.

  • Increased risk of fire due to more collisions between electrons, which raises the circuit's temperature.

  • If a charge fails, other charges continue to function because they each have their own path.

  • Adding more branches and charges will drain the battery faster as it works harder to supply all paths with enough current.