IB PHYSICS Topic 5: Electricity and Magnetism

Electric Charge

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.

Coulomb (C)

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

Conductors

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

Insulators

Materials that 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.

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.

Circuit Diagrams

Diagrams that represent an electric circuit, which is a closed loop of interconnected electrical components.

Resistors

Components that introduce specific resistance in a circuit. They can be connected in series or in parallel.

Voltmeters

Instruments used to measure the potential difference (voltage) between two points in a circuit. They are connected in parallel with the components being measured.

Ammeters

Instruments used to measure current flow in a circuit. They are connected in series at the measurement point.

Kirchhoff's Circuit Laws

Laws that enforce the conservation of charge flow (junction rule) and the conservation of electric potential energy per charge (loop rule) in a circuit.

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, cross-sectional area, and resistivity. Resistivity is a material-specific constant.

Power Dissipation

The power dissipated in a resistor is calculated as P = IV. Electrical energy is converted into heat or other forms of energy.

Cells

Energy sources in a circuit that create an electric potential difference. A battery consists of connected cells.

Secondary Cells

Rechargeable batteries that 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 energy supplied per unit charge by a cell, measured in volts (V).

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

Measured in tesla (T), it indicates the strength and direction of a magnetic field.

Magnetic Field Patterns

Represented using magnetic field lines. The direction and density of field lines indicate the field's strength and direction.

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.

Conventional Current

The direction of current flow opposite to the flow of electrons.

Circular Path

Magnetic forces cause a charge to follow a circular path, acting as a centripetal force. No work is done on the charge by the magnetic field.