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

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?

Practice Time:

  1. Physics Classroom Packet pages 13 & 14
  2. APlusPhysics pages 112-115

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?

Fields, Work, and Potential Energy

center

Gravitational Potential

  • move object up, increase PE
  • move object down, decreases PE
  • quantity that refers great potential of having large quantities of potential energy is called gravitational potential

Electric Potential Energy

  • Work required to move charge towards VDG
  • More charge, more work because more force (W=FdW=Fd)

Electric Potential

  • does not depend on charge, is the energy per unit charge
  • location dependent in the electric field

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

Electric Potential Difference (Voltage)

  • work done from moving charge from A to B would be equal to the change in electric potential energy
  • this work would be scaled by charge, if we consider the work done per unit charge, than that is the electric potential difference

ΔV=VB−VA=WorkCharge=ΔPEq\Delta V = V_B - V_A = \frac{\text{Work}}{\text{Charge}} = \frac{\Delta PE}{q}

Simple Circuits

  • Circuits are about the movement of charges
  • 12 volt battery means then every coulomb of charge is gaining 12 joules of potential energy as it moves through the battery.
  • Every coulomb of charge loses 12 joules of electric potential energy as it passes through the external circuit.
  • What does the loss give us?

Potential Difference (AKA Voltage)

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

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