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IB PHYSICS Topic 5: Electricity and Magnetism
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.
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.
IB PHYSICS Topic 5: Electricity and Magnetism
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.
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.
