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Objectives

  • Name the two types of charge

  • Explain why objects become charged

  • Explain the difference between conductors and insulators

Electrostatic Charge

  • Types of Charge:

    • Positive (+) Charge: Attracts negative charge, repels positive charge.

    • Negative (-) Charge: Attracts positive charge, repels negative charge.

  • Charging Phenomena:

    • Rubbing a balloon against clothes charges it, allowing it to stick to walls and move water streams due to electrostatic phenomena.

    • Charging occurs through friction, where charge imbalance occurs (like charges repel, unlike charges attract).

Resulting Charges from Rubbing Rods

  • Polythene Rods: When rubbed together, two negatively charged polythene rods repel each other.

  • Perspex Rod:

    • Attracted to polythene after rubbing since it acquires a positive charge.

    • Summary of Charging: When rubbed, electrons are transferred creating charged objects; objects can be charged negatively or positively based on electron movement.

Understanding Charge

  • Atomic Structure: An atom consists of protons (positive) and electrons (negative), with neutrons being neutral.

  • Neutral Atom: If an atom has the same number of protons and electrons, it is neutral.

  • Charging Process: Electrons can be moved from one material to another through actions like rubbing, resulting in dual charges on the rubbing materials.

    • Example: Rubbing a polythene rod results in a negative charge on the rod and a positive charge on the cloth used.

Electric Fields

  • Surrounding charges create an electric field, capable of exerting force on other charges.

  • Conductors vs Insulators:

    • Conductors: Allow free movement of electrons (e.g., metals).

    • Insulators: Electrons remain bound to their atoms (e.g., rubber, plastic).

    • Historical Context: In 600 BCE, a Greek scientist discovered electrostatic effects using amber, leading to the term "electron."

Conductors and Insulators in Circuits

  • Circuit Diagrams:

    • Use symbols to represent components (battery, switch, lamp) to make it easier to represent circuits.

  • Conductors: Materials that allow electricity to flow easily.

    • Includes metals such as silver, copper, and graphite (even though it's a form of carbon).

  • Insulators: Materials that resist electrical current (e.g., plastic covering wires for safety).

Electric Current

  • Definition: An electric current is the flow of charge, typically carried by electrons in a metal wire.

  • Measurement:

    • Measured in amperes (A), with smaller currents measured in milliamps (mA).

    • Use an ammeter to measure current in a circuit.

  • Series Circuits: In series circuits, components are connected end-to-end, one loop only. Adding components affects the current.

Changing Current in Circuits

  • Current Behavior: In a series circuit, adding lamps increases resistance, reducing current. More cells provide increased current and energy per charge.

  • Example Observations:

    • With one lamp, normal brightness; adding a second lamp dims the light and decreases current.

    • Adding cells increases current and brightness, demonstrating how circuits function under different configurations.