5.1 - Electric Fields

Electric Charge:

• Electric charge comes in two forms: positive and negative.

• Like charges repel each other, while opposite charges attract.

• An object with equal positive and negative charges is electrically neutral.

• The unit of electric charge is the coulomb (C).

• The charge of one electron is approximately 1.6 × 10^-19 C.

• Electric charge is conserved, meaning the total charge remains constant even as charges move between objects.

• Conductors allow the flow of electric charge due to the presence of free electrons (e.g., metals, graphite, and humans).

• Insulators do not permit the passage of electric charge (e.g., wood, glass, and plastic).

Electric Field:

• Electric fields can be visualized as electric field lines.

• The direction of the field at a point corresponds to the direction of the field line passing through it, typically from the positive pole to the negative pole.

• The density of field lines around a point represents the field's magnitude.

• In a uniform electric field, field lines are straight, parallel, and evenly spaced.

• Non-uniform electric fields result in curved field lines near edges.

• Electric field strength (E) measures the force per unit charge experienced by a positive test charge placed in the field.

• Coulomb's law describes the relationship between electric field strength, force, charges, and distance.
  

5.2 - Heating Effect of Electric Currents

Circuit Diagrams:

• An electric circuit is a closed loop of interconnected electrical components.

Resistors:

• Resistors introduce specific resistance in a circuit.

• Variable resistors have adjustable resistance.

• Resistors can be connected in series or in parallel.

Voltmeters:

• Voltmeters measure the potential difference (voltage) between two points.

  

• They are connected in parallel with the components being measured.

• Ideal voltmeters have infinite resistance.

Ammeters:

• Ammeters measure current flow.

• They are connected in series at the measurement point.

• Ideal ammeters have zero resistance.

Kirchhoff's Circuit Laws:

• Kirchhoff's junction rule enforces the conservation of charge flow.

• Kirchhoff's loop rule ensures the conservation of electric potential energy per charge.

Resistance and Ohm's Law:

• Resistance (R) opposes electric current and is the ratio of potential difference (V) to current (I).

  
  

• Ohm's law states that current is proportional to voltage, with a constant resistance (Ohmic conductor).

• Non-Ohmic conductors exhibit non-linear graphs.

Resistivity:

• Resistance depends on the object's length (L), cross-sectional area (A), and resistivity.

• Resistivity is a material-specific constant.

Power Dissipation:

• Power (P) dissipated in a resistor is calculated as P = IV.

• Electrical energy is converted into heat or other forms of energy.

5.3 - Electric Cells

Cells:

• A cell is an energy source in a circuit, creating an electric potential difference.

• A battery consists of connected cells.

• Internal resistance affects the EMF  (electromotive force) of a cell.

Secondary Cells:

• Secondary cells, or rechargeable batteries, can be recharged by reversing the current flow.

Terminal Potential Difference:

• The potential difference at a cell's terminals is less than its EMF due to internal resistance.

Electromotive Force (emf):

• The emf is the energy supplied per unit charge by a cell.

• It is measured in volts (V).

5.4 - Magnetic Effects of Electric Currents

Magnetic Fields:

• Magnetic fields result from magnets or moving charges.

• Magnets or electric currents experience forces in magnetic fields like electric charges in electric fields.

• Magnetic field strength is measured in tesla (T).

Magnetic Field Patterns:

• Magnetic fields are represented using magnetic field lines.

• The direction and density of field lines indicate the field's strength and direction.

• Magnetic fields can be viewed in 3D with dots (out of the page) and crosses (into the page)
  

Magnetic Force:

• The force on a current-carrying wire in a magnetic field is calculated using the formula F = BIL, where B is the magnetic field, I is the current, and L is the length of the wire.

  

• The force acts perpendicularly to both the wire and the field.

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• The magnetic force on a moving charge is given by F = qvB, where q is the charge, v is the velocity, and B is the magnetic field.

• The direction of conventional current is opposite to electron flow.

• Magnetic forces cause the charge to follow a circular path, acting as a centripetal force.

• No work is done on the charge by the magnetic field.