Skip to main content
Back

Physics: Electricity and Circuits

Control buttons has been changed to "navigation" mode.
1/30
  • Coulomb's Law
    Describes the electrostatic force between two point charges; force magnitude is proportional to the product of charges and inversely proportional to the square of the distance between them.
  • Formula for Coulomb's Law
    Force magnitude: \(F = k_e \frac{|q_1 q_2|}{r^2}\), where k_e is Coulomb's constant.
  • Direction of Electrostatic Force
    Force acts along the line joining charges; like charges repel, unlike charges attract.
  • Electric Field Definition
    The electric field at a point is the force per unit positive charge placed at that point.
  • Electric Field Due to a Point Charge
    Electric field magnitude: \(E = k_e \frac{|q|}{r^2}\); direction is away from positive charges and toward negative charges.
  • Electric Field Lines
    Lines show electric field direction; they start on positive charges and end on negative charges. Density of lines indicates field strength.
  • Electric Field Inside a Conductor
    Inside a conductor in electrostatic equilibrium, the electric field is zero; excess charge resides on the surface.
  • Gauss's Law
    Relates electric flux through a closed surface to the charge enclosed: \(\Phi = \oint \mathbf{E} \cdot d\mathbf{A} = \frac{q_{enc}}{\varepsilon_0}\).
  • Electric Potential Energy
    Energy a charge has due to its position in an electric field.
  • Potential Difference (Voltage)
    Work done per unit charge to move a charge between two points; unit is Volt (V) = Joule/Coulomb.
  • Relation Between Electric Field and Potential
    Electric field is the negative gradient of electric potential: \(\mathbf{E} = -\nabla V\).
  • Electric Potential Due to Point Charges
    Potential at a point is the algebraic sum of potentials from each charge: \(V = k_e \sum \frac{q_i}{r_i}\).
  • Capacitance Definition
    Ability of a system to store charge per unit potential difference; unit is Farad (F).
  • Capacitance Formula
    Capacitance: \(C = \frac{Q}{V}\).
  • Parallel Plate Capacitor Capacitance
    Capacitance: \(C = \varepsilon_0 \frac{A}{d}\), where A is plate area and d is separation.
  • Effect of Dielectrics on Capacitance
    Dielectrics increase capacitance: \(C = \kappa \varepsilon_0 \frac{A}{d}\), where κ is the dielectric constant.
  • Energy Stored in a Capacitor
    Energy: \(U = \frac{1}{2} C V^2\).
  • Electric Current Definition
    Rate of flow of charge through a conductor; unit is Ampere (A) = Coulomb/second.
  • Ohm's Law
    Current through a conductor is proportional to voltage: \(V = IR\).
  • Resistance and Resistivity
    Resistance: \(R = \rho \frac{L}{A}\), where ρ is resistivity, L is length, and A is cross-sectional area.
  • Electromotive Force (EMF) and Terminal Voltage
    EMF is ideal voltage of a source; terminal voltage is actual voltage when current flows: \(V_{terminal} = \mathcal{E} - Ir\), where r is internal resistance.
  • Resistors in Series
    Equivalent resistance: \(R_{eq} = R_1 + R_2 + ...\).
  • Resistors in Parallel
    Equivalent resistance: \(\frac{1}{R_{eq}} = \frac{1}{R_1} + \frac{1}{R_2} + ...\).
  • Kirchhoff's Junction Rule
    Sum of currents entering a junction equals sum leaving it.
  • Kirchhoff's Loop Rule
    Sum of potential differences around any closed loop is zero.
  • Capacitors in Series
    Equivalent capacitance: \(\frac{1}{C_{eq}} = \frac{1}{C_1} + \frac{1}{C_2} + ...\).
  • Capacitors in Parallel
    Equivalent capacitance: \(C_{eq} = C_1 + C_2 + ...\).
  • RC Circuit Charging Equation
    Charge on capacitor during charging: \(Q(t) = Q_0 (1 - e^{-t/RC})\).
  • RC Circuit Discharging Equation
    Charge on capacitor during discharging: \(Q(t) = Q_0 e^{-t/RC}\).
  • Time Constant in RC Circuits
    Time constant: \(\tau = RC\), characterizes charging/discharging rate.