Static Electricity ⚡

A Model for Charged 🎇 Particles




👨‍🏫 Mr. Porter

📆 2025 - Physics








Why does the water bend?

Sticky Tape Lab

  • When Tape is pulled apart the individual pieces of tape become charged.

Sticky Tape Lab

  • When Tape is pulled apart the individual pieces of tape become charged.

🎯 How do these charged pieces of tape interact with each other?

Charge

  • All objects have charge
  • Charge is based on number of protons (➕) or electrons (➖)
  • Charge is negative or positive

Elementary Charge

  • A fundamental property of matter
  • Charge is quantized ➡️ Comes in specific amounts
  • An elementary charge is the smallest sized charge (like a penny in USD)
  • Charge can be measured in:
    • Elementary Charges (ee) (small amounts)
    • Coulombs (CC)


➕ Protons: 1e = 1.6×10−191.6 \times 10^{-19} Coulombs



➖ Electrons: -1e = −1.6×10−19-1.6 \times 10^{-19} Coulombs

❓ Check Your Understanding

How many extra electrons does an object with a charge of −9.6×10−19-9.6 \times 10^{-19} C have?

Conservation of Charge

The total change in a system is constant

Conservation of Charge

❓ What will the charge of each sphere be after the spheres are touched together and removed?

Conservation of Charge

  • Total Charge is conserved
  • Total Charge is distrubuted evenly

Laws of attraction

  1. Opposite Charges Attract
  2. Like Charges Repel
  3. Charge objects always attract neutral objects

Getting Charged

Electroscope

Electroscope Contact Conduction

Induction

Van de Graff Generator

Explain:

  • Why do you get "shocked"
  • Why does the hair stand up?

Coulomb's Law

Fe=kq1q2r2F_e = k\frac{q_1 q_2}{r^2}

  • FeF_e ➡️ electrostatic force
  • kk ➡️ electrostatic constant = 8.99×1098.99 \times 10^{9} Nm2^2/C2^2
  • qq ➡️ charge
  • rr ➡️ distance between the centers

Example:

What is the electrical force between two very small objects located 0.5 m apart when the charge on one object is 4.0 ×\times 10−8^{-8} C and the charge on the second object is 6.0 ×\times 10−5^{-5} C?

Graph Example:

What shows the relationship between the electrostatics force and the distance?

Example:

Two charges attract each other with a force of F. If one charge was doubled and the other charge was tripled, how would that change the attractive force between those charges?

Mapping the Electric Field

  1. Using a ruler measure the distance between the charges.
  2. Calculate the electrostatic force between the two charges.
  3. Draw a scaled vector starting on the test charge that represents the force between the test charge and the central charge.

Note: You can make a spreadsheet to help with the calculations

Electric Field

A region in space where electric forces will act on charges.

Electric Field Lines

Field Lines point in the direction that a positive point charge would experience a force.

Electric Field

E=FeqE = \frac{F_e}{q}

  • EE ➡️ Electric Field Strength (N/C)
  • FeF_e ➡️ Electrostatic Force (N)
  • qq ➡️ Charge of object in field (C)

Comparison to Gravity

E=FeqE = \frac{F_e}{q} vs. g=Fgmg = \frac{F_g}{m}

Example:

What is the magnitude of the electric field intensity at a point in the field where an electron experiences 1 N of force?

Potential & Gravity Comparison

  • What is Potential?
    • What is gravity?
    • Where does it come from?
    • How do you know it is present?
    • What do you change an object's PEgPE_g?
    • What is Earth's gravitational field strength?

Bleacher Example

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Electric Energy

The work needed or energy required by moving a positive charge in an electric field

W=Fd=(qE)d=qV⏞EPE=mgh⏟PEg=12mv2W = Fd = (qE)d = \overbrace{qV}^{\textrm{EPE}} = \underbrace{mgh}_{\textrm{PEg}} = \frac{1}{2}mv^2

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Potential Difference (AKA Voltage)

This is the potential energy difference per unit charge between two points.

V=WqV = \frac{W}{q}