physipics

FIVE:

CIRCUITS

NOTE: These Talk-About Frames are samples of a much larger, and growing, collection. Scroll down to see the current list.

Ins and outs and rounds and rounds of electric circuits

C1: Ins and outs and rounds and rounds of electric circuits

Syllabus / specification points:

• circuits transfer energy to their surroundings; a resistor, such as the thin wire in a filament lamp, transfers energy by heating

• A circuit needs a source of energy, such as a cell or battery

• A circuit operates, and energy transfers, when it carries a current; this requires a complete circuit; a circuit can be broken (or switched off) by opening a switch

• E can stand for energy and I for current

Models of circulation I: money and goods

C1.B: Ins and outs and rounds and rounds of electric circuits

Syllabus / specification points:

• We can’t directly see what’s going on inside wires, so we must use models to understand circuits

• Some models are better matches than others to the observed behaviour of electric circuits

• We should critically evaluate models

Models of circulation II: water

C1.C: models of circulation – water in the environment

Syllabus / specification points:

• Water circulates in the global environment, and the circulation needs a source of energy, which is the Sun

Models of circulation III: blood

C1.D: models of circulation – blood

Syllabus / specification points:

• Blood circulates, ‘pumped’ by the heart

• In different locations in the body, blood gains and loses materials

• There is some resistance to the flow

• Flow of liquid along a pipe can be driven by pressure difference

Models of circulation IV: a delivery route

C1.E: models of circulation – a delivery route

Syllabus / specification points:

• A delivery driver follows a circuit

• At the depot, she collects packages

• At the delivery addresses, she leaves the packages

• There may be resistance to travel, along the route

• It is important to evaluate models

Electric current

C2: Electric current

Syllabus / specification points:

• The current is the same at all points in a single loop (simple series) circuit

• We use ammeters to measure current, and the unit is the amp (ampere), A

• In a circuit in which there are no other changes, increasing resistance reduces current

Current and resistance

C2.B: Current and resistance

Syllabus / specification points:

• If the circuit energy source doesn’t change too much then when resistance in a circuit increases the current decreases.

resistors in series and parallel

C3: Resistors in series and parallel

Syllabus / specification points:

• Resistors connected in series have a resistance to current that is larger than for any one of them alone

• Resistors connected in parallel have a resistance to current that is smaller than for any one of them alone

flow of charged particles

C4: Flow of charged particles

Syllabus / specification points:

• Atoms have electrons, which are very small and all the same, each with negative electric charge

• Atoms normally have a balance of positive and negative charge, and are electrically neutral, but if they lose one or more electrons they become positive ions

• If there are free charged particles, such as electrons and ions, they may flow

• The flow creates an electric current

current in a wire

C5: Current in a wire

Syllabus / specification points:

• There are free electrons and positive ions inside metals

• The ions have fixed locations but the electrons can flow within the metal

• A flow of charged particles such as electrons creates an electric current 

energy transfer from flow

C5.B: Energy transfer from flow

Syllabus / specification points:

• A flow of free electrons in a metal results in many collisions with the metal ions.

• This transfers energy to the ions, so that they vibrate more.

• An increase of vibration of many ions increases the temperature.

• Energy can then transfer to the surroundings by heating (thermal processes)

difference and flow

C6: Difference and flow

Syllabus / specification points:

• Flow from one place to another is created by difference.

• For example, temperature difference produces a flow (transfer) of energy.

• A cell or battery has positive and negative terminals; there is a difference.

• The difference in electric circuits is called potential difference.

• Potential difference produces a flow, a current, when there is a circuit connecting the terminals.

difference and no difference

C6.B: Difference and no difference

Syllabus / specification points:

• Where there is no resistance in a part of a circuit, no potential difference is needed for there to be current

• Where there is resistance there must be a potential difference ‘across’ (between the ends of) the resistor, for there to be current.

• In a simple circuit with a ‘power source’ (such as a cell or battery) and a single resistor, the potential difference across the power source and the potential difference across the resistor are the same size.

Circuits, provisional list, May 2021


Comp: completed and ready, but so far unpublished


C1        The ins and outs and rounds and rounds of electric circuits            FREE

C1.B    Models of circulation I: money and goods                                        FREE

C1.C    Models of circulation II: water                                                           FREE

C1.D    Models of circulation III: blood                                                          FREE

C1.E     Models of circulation IV: a delivery route                                           FREE

C2        Electric current                                                                                  FREE

C2.B    Current and resistance                                                                      FREE

C3        Resistors in series and parallel                                                         FREE

C4        Flow of charged particles                                                                 FREE

C5        Current in a wire                                                                               FREE

C5.B    Energy transfer from flow                                                                  FREE 

C6        Difference and flow                                                                          FREE

C6.B    Difference and no difference                                                            FREE

C6.C    Measuring the difference in a simple circuit                                    Comp

C7        Current, resistance and potential difference I                                 Comp

C7.B    Measuring the difference in a series circuit                                     Comp

C7.C    Measuring the difference in a parallel circuit                                   Comp

C8        Current, resistance and potential difference II                                Comp

C8.B    Circuits and scientific predictions                                                   Comp

C8.C    The meaning of resistance                                                              Comp

C8.D    Where the skill is                                                                             Comp

C9        A linear graph                                                                                  Comp

C10      A filament lamp graph                                                                     Comp

C11      A diode graph                                                                                  Comp

C12    ‘Conventional current’ and electron flow                                          Comp

C13    Current and charge                                                                           Comp

C14    Charge, potential difference, and energy                                          Comp

C15    Electric charge and particles                                                            Comp

C16    Charge and time                                                                               Comp

C17    An energy equation                                                                           Comp

C18    Low power                                                                                        Comp

C19    More power                                                                                      Comp

C20    The kilowatt-hour for measuring energy                                           Comp

C21    Dividing potential                                                                              Comp

C22    A variable resistor                                                                             Comp

C23    Circuits that ‘know’ I: temperature                                                   Comp

C24    Circuits that ‘know’ II: light intensity                                                 Comp 


C30    Field lines                                                                                          Comp

C31    The Earth’s magnetic field                                                                Comp











All ’comp’ (completed) Frames are available at low cost.

Copyright (c) David Brodie, 2019-2021

Photography: Adobe Stock