Lecture 6

Electric Field Lines

  • Visualization of Electric Fields

    • Electric field lines provide a map of how electric fields are distributed in space and time.

    • Lines represent the direction of force experienced by test charges.

  • Direction of Electric Field Lines

    • Lines point away from positive charges and toward negative charges:

      • Positive test charge near a positive source experiences repulsion.

      • Positive test charge near a negative source experiences attraction.

  • Line Density

    • Line density correlates with electric field strength; more lines indicate a stronger field.

    • Examples:

      • A charge +q has fewer lines than a charge +2q, indicating a stronger charge for +2q.

      • Areas without lines indicate a weak or zero electric field.

Electric Field Strength and Charges

  • Electric Field Configuration

    • The configuration is unique for a given system of charges and does not cross.

    • Strong regions of the electric field occur between opposite charges (e.g., +4q and -2q).

  • Uniform Electric Fields

    • An example is a positively charged plane where the electric field above points upward and below points downward.

Applications of Electric Fields in Nature

  • Behavior in Biological Systems

    • Certain species navigate using the electric fields of air/magnetic fields during migration.

      • Example: Birds and monarch butterflies use magnetic field lines for direction.

      • Birds may experience electron spin changes in a chemical reaction based on magnetic fields.

  • Sharks

    • Sharks utilize the ampullae of Lorenzini to detect electrical fields and magnetic fields, aiding in prey detection.

  • Platypus

    • Platypuses locate shrimp by sensing electric field distortions in murky waters.

  • Electric Eels

    • Electric eels create an electric field to sense the presence of other animals, which affects their hunting ability.

  • Spiders

    • Recent research shows that spiders can traverse distances utilizing the electric fields through a phenomenon known as ballooning:

      • Spiders release silk that becomes charged, causing them to be lifted by electric fields in the atmosphere.

Effect of Electric Fields on Charges

  • Movement Under Electric Fields

    • Charged particles experience forces when they move through electric fields.

  • Inkjet Printers as an Example

    • Ink droplets are charged to ensure they stick to the paper during printing.

  • Kinematic Analysis

    • Analyze the motion of the charge droplet affected by electric fields to determine their position change (deflection).

  • Electric Field Equations and Calculations

    • Use Newton's laws and kinematic equations to analyze the motion of charged particles (ink droplets).

  • Acceleration Calculation

    • Acceleration is derived from the force exerted by the electric field on the droplet, considering its mass.

  • Deflection Calculation

    • Conclude with the calculation for the vertical deflection of the ink drop across the parallel plates.

  • Result

    • Final calculation yields a deflection of approximately 0.64 millimeters.

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