2.5 Electric potential

Electric potential is a crucial concept in electrostatics, describing the potential energy per unit charge at a point in an electric field. It relates to work done by electric forces and plays a key role in understanding electrical circuits and energy transfer in electromagnetic systems.

Electric potential difference, or voltage, measures the change in electric potential between two points. It drives electric current flow in circuits and determines energy transfer between electrical components. Voltage is measured in volts, with one volt equaling one joule per coulomb.

Definition of electric potential

• Electric potential forms a fundamental concept in electrostatics describing the potential energy per unit charge at a point in an electric field
• Relates to the work done by electric forces and plays a crucial role in understanding electrical circuits and energy transfer in electromagnetic systems

Potential energy vs kinetic energy

Top images from around the web for Potential energy vs kinetic energy

• 

  19.4 Equipotential Lines – College Physics View original

  Is this image relevant?

• 

  3.1 Electric Potential Energy: Potential Difference – Douglas College Physics 1207 View original

  Is this image relevant?

• 

  7.1 Electric Potential Energy: Potential Difference – Douglas College Physics 1207 View original

  Is this image relevant?

• 

  19.4 Equipotential Lines – College Physics View original

  Is this image relevant?

• 

  3.1 Electric Potential Energy: Potential Difference – Douglas College Physics 1207 View original

  Is this image relevant?

1 of 3

Top images from around the web for Potential energy vs kinetic energy

• 

  19.4 Equipotential Lines – College Physics View original

  Is this image relevant?

• 

  3.1 Electric Potential Energy: Potential Difference – Douglas College Physics 1207 View original

  Is this image relevant?

• 

  7.1 Electric Potential Energy: Potential Difference – Douglas College Physics 1207 View original

  Is this image relevant?

• 

  19.4 Equipotential Lines – College Physics View original

  Is this image relevant?

• 

  3.1 Electric Potential Energy: Potential Difference – Douglas College Physics 1207 View original

  Is this image relevant?

1 of 3

• Potential energy represents stored energy due to position or configuration within a force field
• Kinetic energy denotes the energy of motion possessed by moving objects
• In electrostatics, charges can convert between potential and kinetic energy as they move through electric fields
• Relationship between potential and kinetic energy governs the behavior of charged particles in accelerators and electronic devices

Work and electric potential

• Electric potential directly relates to the work done by electric forces to move a charge
• Work done against the electric field increases the potential energy of a charge
• Defined mathematically as the work per unit charge required to move a test charge from a reference point to a specific location
• Measured in joules per coulomb (J/C) or volts (V)

Electric potential difference

• Electric potential difference, also known as voltage, measures the change in electric potential between two points in an electric field
• Drives the flow of electric current in circuits and determines the energy transfer between electrical components

Voltage concept

• Represents the electric potential energy difference per unit charge between two points
• Analogous to the difference in gravitational potential energy between two heights
• Determines the force experienced by charges placed in an electric field
• Can be positive, negative, or zero depending on the relative potentials of the points considered

Units of electric potential

• Measured in volts (V), named after Alessandro Volta
• One volt equals one joule per coulomb (1 V = 1 J/C)
• Common multiples include millivolts (mV) and kilovolts (kV)
• Voltage sources (batteries, power supplies) rated in volts indicate their ability to maintain a potential difference

Equipotential surfaces

• Equipotential surfaces represent regions in space where the electric potential remains constant
• Understanding equipotential surfaces aids in visualizing electric fields and predicting the motion of charged particles

Equipotential lines in 2D

• Represent contours of constant electric potential in a two-dimensional plane
• Always perpendicular to electric field lines
• Closer spacing between equipotential lines indicates stronger electric fields
• Used in electrostatic field mapping and analyzing charge distributions

Equipotential surfaces in 3D

• Three-dimensional extensions of equipotential lines
• Form closed surfaces around charge distributions
• Spherical for point charges, cylindrical for line charges, and planar for uniform field regions
• Help visualize the potential landscape in complex three-dimensional charge configurations

Calculating electric potential

• Determining electric potential involves integrating the electric field or summing contributions from individual charges
• Requires choosing a reference point where the potential is defined as zero (typically infinity or ground)

Point charges

• Electric potential due to a point charge given by $V = k\frac{q}{r}$
• k represents Coulomb's constant, q the charge, and r the distance from the charge
• Decreases inversely with distance, following a 1/r relationship
• Positive for positive charges, negative for negative charges

Continuous charge distributions

• Involves integrating the contributions from infinitesimal charge elements
• Requires knowledge of charge density (linear, surface, or volume)
• Often utilizes symmetry to simplify calculations
• Examples include calculating potential for charged rods, disks, and spheres

Superposition principle

• Total electric potential at a point equals the sum of potentials due to individual charges
• Allows breaking complex charge distributions into simpler components
• Mathematically expressed as $V_{total} = V_1 + V_2 + V_3 + ...$
• Applies to both discrete charges and continuous charge distributions

Electric field vs potential

• Electric field and potential are closely related but distinct concepts in electrostatics
• Understanding their relationship aids in solving complex electrostatic problems

Relationship between E and V

• Electric field represents the force per unit charge, while potential represents energy per unit charge
• Electric field points from high to low potential regions
• Magnitude of electric field relates to the rate of change of potential with distance
• Work done by the electric field equals the negative change in potential energy

Gradient of potential

• Electric field equals the negative gradient of electric potential
• Mathematically expressed as $\vec{E} = -\nabla V$
• In Cartesian coordinates: $\vec{E} = -(\frac{\partial V}{\partial x}\hat{i} + \frac{\partial V}{\partial y}\hat{j} + \frac{\partial V}{\partial z}\hat{k})$
• Allows calculation of electric field from known potential distributions

Potential energy of charge systems

• Potential energy in electrostatic systems arises from the configuration of charges
• Calculating potential energy helps determine stability and energy storage in charge distributions

Two-charge systems

• Potential energy of two point charges given by $U = k\frac{q_1q_2}{r}$
• Positive for like charges (repulsive), negative for opposite charges (attractive)
• Represents work required to bring charges from infinity to their final separation
• Forms the basis for understanding more complex multi-charge systems

Multiple-charge systems

• Total potential energy found by summing pairwise interactions between all charges
• Mathematically expressed as $U_{total} = \frac{1}{2}\sum_{i}\sum_{j\neq i} k\frac{q_iq_j}{r_{ij}}$
• Factor of 1/2 prevents double-counting of interactions
• Applies to discrete charge arrangements and continuous charge distributions

Conductors and electric potential

• Conductors play a unique role in electrostatics due to the mobility of their charge carriers
• Understanding conductor behavior aids in designing electrical components and shielding devices

Equipotential nature of conductors

• In electrostatic equilibrium, the entire volume and surface of a conductor form an equipotential region
• Ensures no electric field exists inside the conductor (electrostatic shielding)
• Any potential difference within a conductor causes charge redistribution until equilibrium
• Allows for charge sharing and capacitive effects in electrical circuits

Charge distribution on conductors

• Excess charge on a conductor resides entirely on its surface
• Charge density varies with surface curvature, higher on sharper regions (lightning rod effect)
• Hollow conductors have no internal electric field, regardless of external fields
• Forms the basis for Faraday cages and electromagnetic shielding techniques

Capacitance and potential

• Capacitance measures a system's ability to store electric charge for a given potential difference
• Plays a crucial role in energy storage devices and electrical circuit components

Definition of capacitance

• Ratio of stored charge to applied voltage: $C = \frac{Q}{V}$
• Measured in farads (F), with 1 F = 1 C/V
• Depends on geometry and dielectric properties of the capacitor
• Typical capacitors range from picofarads (pF) to microfarads (μF)

Parallel plate capacitor

• Simplest capacitor design consisting of two parallel conducting plates separated by a dielectric
• Capacitance given by $C = \frac{\epsilon_0 A}{d}$, where A is plate area and d is separation
• Electric field between plates approximately uniform for small d/A ratios
• Forms the basis for understanding more complex capacitor geometries (cylindrical, spherical)

Applications of electric potential

• Electric potential concepts find widespread use in various technological applications
• Understanding these applications helps connect theoretical concepts to real-world devices

Electron volt as energy unit

• Defined as the energy gained by an electron moving through a potential difference of 1 volt
• Equals 1.602 × 10^-19 joules
• Commonly used in atomic and particle physics
• Useful for describing energies of subatomic particles and chemical bonds

Cathode ray tubes

• Early display technology utilizing accelerated electrons
• Electrons emitted from a heated cathode and accelerated by high voltage
• Deflected by electric or magnetic fields to create images on a phosphor screen
• Demonstrates principles of electron optics and potential difference effects

Particle accelerators

• Devices using electric potentials to accelerate charged particles to high energies
• Linear accelerators use a series of increasing potentials to accelerate particles
• Circular accelerators (cyclotrons, synchrotrons) combine magnetic fields with radio-frequency electric fields
• Enable studies in particle physics, materials science, and medical treatments

Electrostatic potential energy

• Represents the stored energy in a system of charges due to their relative positions
• Crucial for understanding stability and energy transfer in electrostatic systems

Conservation of energy

• Total energy (kinetic + potential) remains constant in isolated electrostatic systems
• Charges moving in electric fields convert between potential and kinetic energy
• Allows prediction of particle velocities and trajectories in electric fields
• Forms the basis for energy calculations in particle accelerators and electron microscopes

Potential energy in electric fields

• Calculated by integrating the work done against the electric field
• For a point charge q in an external field: $U = qV$
• For a continuous charge distribution: $U = \int \rho V dV$, where ρ is charge density
• Determines the stability and binding energies of atomic and molecular systems

Dielectrics and electric potential

• Dielectric materials modify the electric field and potential distributions in capacitors
• Understanding dielectric effects aids in designing high-performance capacitors and insulation systems

Effect on capacitance

• Dielectrics increase capacitance by a factor κ (dielectric constant)
• New capacitance: $C = \kappa C_0$, where C_0 is the capacitance without dielectric
• Reduces the electric field inside the capacitor by polarizing the dielectric material
• Allows for smaller capacitors with higher capacitance values

Energy storage in dielectrics

• Dielectrics increase the energy storage capacity of capacitors
• Energy stored in a capacitor with dielectric: $U = \frac{1}{2}CV^2 = \frac{1}{2}\kappa C_0V^2$
• Dielectric breakdown occurs when the electric field exceeds the material's dielectric strength
• Determines the maximum operating voltage and energy density of capacitive storage devices