Overview
This lecture introduces electrostatics, focusing on atomic charge, the calculation of electric force between charges, and unit conversions for charge.
Structure of an Atom
- Atoms have a nucleus containing protons (positive) and neutrons (neutral).
- Electrons (negative) orbit outside the nucleus.
- The overall charge of an atom is determined by the balance of protons and electrons.
- Atoms with equal numbers of protons and electrons are neutral.
Charge Interactions
- Atoms or ions with net charges exert forces on each other (attraction or repulsion).
- Opposite charges attract; like charges repel.
- The magnitude of force depends on the amount and type of charge each atom/ion carries.
Calculating Electric Force
- The force (( F )) between two charges is given by ( F = k \frac{q_1 q_2}{r^2} ).
- ( k ) is a constant: ( 9 \times 10^9 ) (provided on your formula sheet).
- ( q_1 ) and ( q_2 ) are the magnitudes of the charges (omit negative signs in the formula).
- ( r ) is the distance between the charges in meters.
- The result is given in Newtons (N).
- Do not include the sign of the charge when calculating the magnitude of the force.
Charge Units and Conversion
- Standard unit for charge is coulomb (C).
- Common alternatives: millicoulomb (mC), microcoulomb (μC), nanocoulomb (nC), and picocoulomb (pC).
- Convert to coulombs as follows:
- mC: multiply by ( 10^{-3} )
- μC: multiply by ( 10^{-6} )
- nC: multiply by ( 10^{-9} )
- pC: multiply by ( 10^{-12} )
- Remember the pattern: 3, 6, 9, 12 for exponents.
Key Terms & Definitions
- Proton — positively charged particle in the nucleus.
- Neutron — neutral particle in the nucleus.
- Electron — negatively charged particle outside the nucleus.
- Coulomb (C) — standard unit of electric charge.
- Electric Force — the force between two charged objects.
- Newton (N) — unit for force.
Action Items / Next Steps
- Memorize the conversion factors for millicoulomb, microcoulomb, nanocoulomb, and picocoulomb to coulomb.
- Review the electric force formula and practice using it with different units.