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.