Electric Forces and Charging Tape Notes

Electric Forces

  • The electric interaction underlies many everyday phenomena, including electricity, contact forces, and light.
  • Despite its omnipresence, these interactions are often not directly perceived.

Charging Objects

  • Ordinary objects can acquire either an excess of negative charge (negatively charged) or a deficiency of negative charge (net positive charge) when rubbed, pulled, or touched.
  • This experiment aims to explore electric (Coulomb) interactions by charging strips of invisible tape.

Measuring Charge on Tape

  • The net excess charge on a piece of tape falls within the range of charge of one electron (minimum 1.6 imes 10^{-19} C) and the charge left if all electrons were removed (maximum approximately 1 imes 10^5 C).
  • This represents a large range that needs to be quantified.

Preparing the Tape

  1. Base Tape

    • Cut a strip of tape about 20 cm long.
    • Fold under one end to create a non-sticky handle.
    • Stick the tape firmly on a smooth surface and smooth it down with your fingers.

  2. Upper Tape (U Tape)

    • Cut another 20 cm piece and prepare a handle as before.
    • Stick U tape directly on top of the base tape and ensure it is smooth.
    • Mark the handle with the letter "U".

  3. Interaction with the Hand

    • Quickly pull U tape from base tape and hang it vertically.
    • Bring your hand near to see if there's an attraction (if not, remake U tape).

Observations of Interaction

  • Prediction: Discuss expectations about the behavior when two U tapes are brought near each other.
  • Prepare a second U tape and observe the interaction. Predict and confirm observations.
  • Test U tape against neutral objects (like your hand or a table).

Charge Classification

  • When rubbing clear plastic with hair or fur, the plastic becomes negatively charged, influencing its interactions.
  • Explore Charge Possibilities:
    • Predict interactions based on charge (positive, negative, or neutral) of U tape when brought near a negatively charged plastic pen.
    • After experimenting, determine your U tape's charge based on observations.

Calculating Charge

  • Consider tape B as a floating system above tape A.
  • Draw a force diagram of floating tape B, identifying vertical forces acting on it.
  • Set up Newton’s 2nd Law to determine net force F_{ ext{net}}.
  • Keep in mind:
    1. Both tapes assumed to have the same net charge.
    2. Excess charge is concentrated at a point.
  • Quantities to Measure: Identify what measurements are needed to calculate charge on tape B.
  • Calculating Charge: Use the linear mass density of tape (approximately _{ ext{tape}} ext{~} ext{1.08 g/m}) to determine total charge.
  • Finally, calculate how many electrons have been gained or lost by tape B.