Topic 5 & 11

Topic 5: Electricity and Magnetism

5.1 – Electric fields
5.1 Essential idea: When charges move an electric current is created.

5.1 Nature of science:
Modelling: Electrical theory demonstrates the scientific thought involved in the development of a microscopic model (behaviour of charge carriers) from macroscopic observation. The historical development and refinement of these scientific ideas when the microscopic properties were unknown and unobservable is testament to the deep thinking shown by the scientists of the time. (1.10)

5.1 Understandings:
• Charge
• Electric field
• Coulomb’s law
• Electric current
• Direct current (dc)
• Potential difference

The Coulomb’s law experiment

Five rules of the electric field

Studynova lectures on E & M (SL, core)

5.1 Applications and skills:
• Identifying two forms of charge and the direction of the forces between them

Static electricity labs/activities from The Physics Classroom

• Solving problems involving electric fields and Coulomb’s law

Interaction between electric charges, quantitative investigations, activities, labs
The Physics Aviary Electric Force
PhET Coulomb’s law
Electric (Coulomb) force vs. electric charges | Electric force vs. distance between the charges

Practice problems
https://www.thephysicsaviary.com/Physics/Programs/Labs/CoulombsLawLab/
https://www.thephysicsaviary.com/Physics/APPrograms/ForceElectricTriangle/
https://www.thephysicsaviary.com/Physics/APPrograms/ForceElectricLine/
https://www.thephysicsaviary.com/Physics/APPrograms/ForceElectricBox/
https://www.thephysicsaviary.com/Physics/APPrograms/ChargeCausingElectricField/

Mapping the electric field and electric potential activity
http://dev.physicslab.org/Document.aspx?doctype=2&filename=Electrostatics_ElectricfieldMapping2.xml

• Calculating work done in an electric field in both joules and electronvolts

Quantitative investigation E vs. d, V vs. d, strength of the electric field vs. distance | Electric potential (voltage) vs. distance

• Identifying sign and nature of charge carriers in a metal
• Identifying drift speed of charge carriers
• Solving problems using the drift speed equation
• Solving problems involving current, potential difference and charge

Electric field hockey

5.1 International-mindedness:
• Electricity and its benefits have an unparalleled power to transform society

5.1 Theory of knowledge:
• Early scientists identified positive charges as the charge carriers in metals; however, the discovery of the electron led to the introduction of “conventional” current direction. Was this a suitable solution to a major shift in thinking? What role do paradigm shifts play in the progression of scientific
knowledge?

5.1 Utilization:
• Transferring energy from one place to another (see Chemistry option C and Physics topic 11)
• Impact on the environment from electricity generation (see Physics topic 8 and Chemistry option sub-topic C2)
• The comparison between the treatment of electric fields and gravitational fields (see Physics topic 10)

5.1 Guidance:
• Students will be expected to apply Coulomb’s law for a range of permittivity values

5.1 Data booklet reference:

5.1 Aims:
• Aim 2: electrical theory lies at the heart of much modern science and engineering
• Aim 3: advances in electrical theory have brought immense change to all societies
• Aim 6: experiments could include (but are not limited to): demonstrations showing the effect of an electric field (eg. using semolina); simulations involving the placement of one or more point charges and determining the resultant field
• Aim 7: use of computer simulations would enable students to measure microscopic interactions that are typically very difficult in a school laboratory situation


5.2 – Heating effect of electric currents
5.2 Essential idea: One of the earliest uses for electricity was to produce light and heat. This technology continues to have a major impact on the lives of people around the world.

5.2 Nature of science:
Peer review: Although Ohm and Barlow published their findings on the nature of electric current around the same time, little credence was given to Ohm. Barlow’s incorrect law was not initially criticized or investigated further. This is a reflection of the nature of academia of the time, with physics in Germany being largely non-mathematical and Barlow held in high respect in England. It indicates the need for the publication and peer review of research findings in recognized scientific journals. (4.4)

5.2 Understandings:
• Circuit diagrams
• Kirchhoff’s circuit laws
• Heating effect of current and its consequences
• Resistance expressed as R=V/I
• Ohm’s law
• Resistivity
• Power dissipation

5.2 Applications and skills:
• Drawing and interpreting circuit diagrams
• Identifying ohmic and non-ohmic conductors through a consideration of the V/I characteristic graph

Ohm’s law, linear function
Practice with ohm’s law and wire resistance , meaning of graphs

• Solving problems involving potential difference, current, charge, Kirchhoff’s circuit laws, power, resistance and resistivity

Investigate the resistance of a wire (how resistance depends on size, shape, material)
Or,
Resistance vs. length | Resistance vs. thickness (diameter)
Resistance vs. type of material
Electric equivalent of heat
Power of light bulb

• Investigating combinations of resistors in parallel and series circuits

Elctric ciruits, The Physics Classroom
The Physics Classroom Circuit Builder , 5 activities

• Describing ideal and non-ideal ammeters and voltmeters
• Describing practical uses of potential divider circuits, including the advantages of a potential divider over a series resistor in controlling a simple circuit
• Investigating one or more of the factors that affect resistance experimentally

5.2 International-mindedness:
• A set of universal symbols is needed so that physicists in different cultures can readily communicate ideas in science and engineering

5.2 Theory of knowledge:
• Sense perception in early electrical investigations was key to classifying the effect of various power sources; however, this is fraught with possible irreversible consequences for the scientists involved. Can we still ethically and safely use sense perception in science research?

5.2 Utilization:
• Although there are nearly limitless ways that we use electrical circuits, heating and lighting are two of the most widespread
• Sensitive devices can employ detectors capable of measuring small variations in potential difference and/or current, requiring carefully planned circuits and high precision components

5.2 Guidance:
• The filament lamp should be described as a non-ohmic device; a metal wire at a constant temperature is an ohmic device
• The use of non-ideal voltmeters is confined to voltmeters with a constant but finite resistance
• The use of non-ideal ammeters is confined to ammeters with a constant but non-zero resistance
• Application of Kirchhoff’s circuit laws will be limited to circuits with a maximum number of two source-carrying loops

5.2 Data book reference:

5.2 Aims:
• Aim 2: electrical theory and its approach to macro and micro effects characterizes much of the physical approach taken in the analysis of the universe
• Aim 3: electrical techniques, both practical and theoretical, provide a relatively simple opportunity for students to develop a feeling for the arguments of physics
• Aim 6: experiments could include (but are not limited to): use of a hot-wire ammeter as an historically important device; comparison of resistivity of a variety of conductors such as a wire at constant temperature, a filament lamp, or a graphite pencil; determination of thickness of a pencil mark on paper;
investigation of ohmic and non-ohmic conductor characteristics; using a resistive wire wound and taped around the reservoir of a thermometer to relate wire resistance to current in the wire and temperature of wire
• Aim 7: there are many software and online options for constructing simple and complex circuits quickly to investigate the effect of using different components within a circuit


5.3 – Electric cells
5.3 Essential idea: Electric cells allow us to store energy in a chemical form.

5.3 Nature of science:
Long-term risks: Scientists need to balance the research into electric cells that can store energy with greater energy density to provide longer device lifetimes with the long-term risks associated with the disposal of the chemicals involved when batteries are discarded. (4.8)

5.3 Understandings:
• Cells
• Internal resistance
• Secondary cells
• Terminal potential difference
• Electromotive force (emf)

5.3 Applications and skills:
• Investigating practical electric cells (both primary and secondary)
• Describing the discharge characteristic of a simple cell (variation of terminal potential difference with time)
• Identifying the direction of current flow required to recharge a cell
• Determining internal resistance experimentally
• Solving problems involving emf, internal resistance and other electrical quantities

5.3 Guidance:
• Students should recognize that the terminal potential difference of a typical practical electric cell loses its initial value quickly, has a stable and constant value for most of its lifetime, followed by a rapid decrease to zero as the cell discharges completely

5.3 Data booklet reference:

5.3 International-mindedness:
• Battery storage is important to society for use in areas such as portable devices, transportation options and back-up power supplies for medical facilities

5.3 Theory of knowledge:
• Battery storage is seen as useful to society despite the potential environmental issues surrounding their disposal. Should scientists be held morally responsible for the long-term consequences of their inventions and discoveries?

5.3 Utilization:
• The chemistry of electric cells (see Chemistry sub-topics 9.2 and C.6)

5.3 Aims:
• Aim 6: experiments could include (but are not limited to): investigation of simple electrolytic cells using various materials for the cathode, anode and electrolyte; software-based investigations of electrical cell design; comparison of the life expectancy of various batteries
• Aim 8: although cell technology can supply electricity without direct contribution from national grid systems (and the inherent carbon output issues), safe disposal of batteries and the chemicals they use can introduce land and water pollution problems
• Aim 10: improvements in cell technology has been through collaboration with chemists


5.4 – Magnetic effects of electric currents
5.4 Essential idea: The effect scientists call magnetism arises when one charge moves in the vicinity of another moving charge.

5.4 Nature of science:
Models and visualization: Magnetic field lines provide a powerful visualization of a magnetic field. Historically, the field lines helped scientists and engineers to understand
a link that begins with the influence of one moving charge on another and leads onto relativity. (1.10)

5.4 Understandings:
• Magnetic fields
• Magnetic force

5.4 Applications and skills:
• Determining the direction of force on a charge moving in a magnetic field

Investigate charge moving through a magnetic field, Lorentz force
Magnetic force vs. magnetic field
Magnetic force vs. electric charge
Magnetic force vs. speed

Investigate the radius of curvature as a function of m, v, q, and B
https://www.geogebra.org/m/p7jG2u2Q
https://www.geogebra.org/m/dFQG5amD

• Determining the direction of force on a current-carrying conductor in a magnetic field
• Sketching and interpreting magnetic field patterns

Use The Physics Classroom Magnetism Interactive to draw the magnetic field around a bar magnet.
Qualitative investigation of the magnetic field (B)

• Determining the direction of the magnetic field based on current direction

Quantitative investigation of the electromagnetic field
B (Tesla) vs. distance (cm)
B (T) vs. electric current (A)

• Solving problems involving magnetic forces, fields, current and charges

5.4 Guidance:
• Magnetic field patterns will be restricted to long straight conductors, solenoids, and bar magnets

5.4 Data booklet reference:

5.4 International-mindedness:
• The investigation of magnetism is one of the oldest studies by man and was used extensively by voyagers in the Mediterranean and beyond thousands of years ago

5.4 Theory of knowledge:
• Field patterns provide a visualization of a complex phenomenon, essential to an understanding of this topic. Why might it be useful to regard knowledge in a similar way, using the metaphor of knowledge as a map – a simplified representation of reality?

5.4 Utilization:
• Only comparatively recently has the magnetic compass been superseded by different technologies after hundreds of years of our dependence on it
• Modern medical scanners rely heavily on the strong, uniform magnetic fields produced by devices that utilize superconductors
• Particle accelerators such as the Large Hadron Collider at CERN rely on a variety of precise magnets for aligning the particle beams

5.4 Aims:
• Aims 2 and 9: visualizations frequently provide us with insights into the action of magnetic fields; however, the visualizations themselves have their own limitations
• Aim 7: computer-based simulations enable the visualization of electromagnetic fields in three-dimensional space


Topic 11: Electromagnetic Induction (HL)
11.1 Electromagnetic Induction

11.1 Essential idea: The majority of electricity generated throughout the world is generated by machines that were designed to operate using the principles of electromagnetic induction

11.1 Nature of science:
Experimentation: In 1831 Michael Faraday, using primitive equipment, observed a minute pulse of current in one coil of wire only when the current in a second coil of wire was switched on or off but nothing while a constant current was established. Faraday’s observation of these small transient currents led him to perform experiments that led to his law of electromagnetic induction. (1.8)

11.1 Understandings:
• Electromotive force (emf)
• Magnetic flux and magnetic flux linkage
• Faraday’s law of induction
• Lenz’s law

Studynova lectures on E & M (HL-Electromagnetic Induction)

https://www.rigb.org/our-history/michael-faraday

Electrical timeline in the UK
http://www.engineering-timelines.com/how/electricity/timeline.asp

11.1 Applications and skills:
• Describing the production of an induced emf by a changing magnetic flux and within a uniform magnetic field
• Solving problems involving magnetic flux, magnetic flux linkage and Faraday’s law
• Explaining Lenz’s law through the conservation of energy

11.1 Theory of knowledge:
• Terminology used in electromagnetic field theory is extensive and can confuse people who are not directly involved. What effect can lack of clarity in terminology have on communicating scientific concepts to the public?

11.1 Utilization:
• Applications of electromagnetic induction can be found in many places including transformers, electromagnetic braking, geo-phones used in seismology, and metal detectors

11.1 Aims:
• Aim 2: the simple principles of electromagnetic induction are a powerful aspect of the physicist’s or technologist’s armoury when designing systems that transfer energy from one form to another

11.1 Guidance:
• Quantitative treatments will be expected for straight conductors moving at right angles to magnetic fields and rectangular coils moving in and out of fields and rotating in fields
• Qualitative treatments only will be expected for fixed coils in a changing magnetic field and ac generators

11.1 Data booklet reference:


11.2 Power generation and transmission

11.2 Essential idea: Generation and transmission of alternating current (ac) electricity has transformed the world.

11.2 Nature of science:
Bias: In the late 19th century Edison was a proponent of direct current electrical energy transmission while Westinghouse and Tesla favoured alternating current transmission. The so called “battle of currents” had a significant impact on today’s society. (3.5)

11.2 Understandings:
• Alternating current (ac) generators
• Average power and root mean square (rms) values of current and voltage
• Transformers
• Diode bridges
• Half-wave and full-wave rectification

11.2 Applications and skills:
• Explaining the operation of a basic ac generator, including the effect of
changing the generator frequency
• Solving problems involving the average power in an ac circuit
• Solving problems involving step-up and step-down transformers
• Describing the use of transformers in ac electrical power distribution
• Investigating a diode bridge rectification circuit experimentally
• Qualitatively describing the effect of adding a capacitor to a diode bridge rectification circuit

11.2 Guidance:
• Calculations will be restricted to ideal transformers but students should be aware of some of the reasons why real transformers are not ideal (for example: flux leakage, joule heating, eddy current heating, magnetic hysteresis)
• Proof of the relationship between the peak and rms values will not be expected

11.2 International-mindedness:
• The ability to maintain a reliable power grid has been the aim of all governments since the widespread use of electricity started

11.2 Theory of knowledge:
• There is continued debate of the effect of electromagnetic waves on the health of humans, especially children. Is it justifiable to make use of scientific advances even if we do not know what their long-term
consequences may be?

11.2 Aims:
• Aim 6: experiments could include (but are not limited to): construction of a basic ac generator; investigation of variation of input and output coils on a transformer; observing Wheatstone and Wien bridge circuits
• Aim 7: construction and observation of the adjustments made in very large electricity distribution systems are best carried out using computer-modelling software and websites
• Aim 9: power transmission is modeled using perfectly efficient systems but no such system truly exists. Although the model is imperfect, it renders the maximum power transmission. Recognition of, and accounting for, the differences between the “perfect” system and the practical system is one of the main functions of professional scientists

11.2 Data booklet reference:


11.3 Capacitance

11.3 Essential idea: Capacitors can be used to store electrical energy for later use.

11.3 Nature of science:
Relationships: Examples of exponential growth and decay pervade the whole of science. It is a clear example of the way that scientists use mathematics to model reality. This topic can be used to create links between physics topics but also to uses in chemistry, biology, medicine and economics. (3.1)

11.3 Understandings:
• Capacitance
• Dielectric materials
• Capacitors in series and parallel
• Resistor-capacitor (RC) series circuits
• Time constant

11.3 Applications and skills:
• Describing the effect of different dielectric materials on capacitance
• Solving problems involving parallel-plate capacitors
• Investigating combinations of capacitors in series or parallel circuits
• Determining the energy stored in a charged capacitor
• Describing the nature of the exponential discharge of a capacitor
• Solving problems involving the discharge of a capacitor through a fixed resistor
• Solving problems involving the time constant of an RC circuit for charge, voltage and current

11.3 International-mindedness:
• Lightning is a phenomenon that has fascinated physicists from Pliny through Newton to Franklin. The charged clouds form one plate of a capacitor with other clouds or Earth forming the second plate. The frequency of lightning strikes varies globally, being particularly prevalent in equatorial regions. The
impact of lightning strikes is significant, with many humans and animals being killed annually and huge financial costs to industry from damage to buildings, communication and power transmission systems, and delays or the need to reroute air transport.

11.3 Utilization:
• The charge and discharge of capacitors obeys rules that have parallels in other branches of physics including radioactivity (see Physics sub-topic 7.1)

11.3 Aims:
• Aim 3: the treatment of exponential growth and decay by graphical and algebraic methods offers both the visual and rigorous approach so often characteristic of science and technology
• Aim 6: experiments could include (but are not limited to): investigating basic RC circuits; using a capacitor in a bridge circuit; examining other types of capacitors; verifying time constant

11.3 Guidance:
• Only single parallel-plate capacitors providing a uniform electric field, in series with a load, need to be considered (edge effect will be neglected)
• Problems involving the discharge of capacitors through fixed resistors need to be treated both graphically and algebraically
• Problems involving the charging of a capacitor will only be treated graphically
• Derivation of the charge, voltage and current equations as a function of time is not required

11.3 Data booklet reference:


Additional resources for topic 5 & 11
http://web.mit.edu/8.02t/www/802TEAL3D/index.html

http://vlab.amrita.edu/index.php?sub=1&brch=192

https://www.walter-fendt.de/html5/phen/

AP YouTube channel
https://apcoronavirusupdates.collegeboard.org/students/ap-course-schedule
zoom lectures during covid