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THE IB SAYS
THE IB SAYS
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.
Understandings: Circuit diagrams
Applications and skills: Drawing and interpreting circuit diagrams; Describing ideal and non-ideal ammeters and voltmeters
Guidance: 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
Data booklet equations: None, but see the circuit symbols on page 4 of the physics data booklet
My vodcast
My vodcast
The heating effect of an electrical current
The heating effect of an electrical current
This section of the topic deals further with the concepts of electrical potential, current, power and resistance introduced in the previous section. In any functional and useful circuit, energy will be transferred. All of that energy will eventually be dissipated into the universe as degraded energy (energy that is no longer possible to use to do work) in the form of heat. This is another consequence of the second law of thermodynamics.
Circuit diagrams and circuit symbols
Circuit diagrams and circuit symbols
Circuit symbols are pictograms arranged in circuit diagrams that show the electrical connections between the different components. It is important to remember that, like a map of a public transport system, a circuit diagram includes all the components and connections, but does not preserve scale or the geographical arrangement of the components.
The IB preferred symbols match the most common international system (that of the IEC). The only significant difference with other symbols that you might find in textbooks is with the resistors in the American ANSI system that resemble squiggly lines rather than the boxes of the IB / IEC diagrams.
Some rules for drawing circuit diagrams with a pencil / ruler (as you may need to in exams). In lab reports / notes I recommend the CIRCUIT DIAGRAM software and website.
Use a ruler / sharp pencil or a software package
Leads and layout almost always vertical or horizontal
Don’t write the names of components (unless possibility of confusion)
Do write values of units
Draw a dot where leads join
Try not to cross non-connecting leads
IMPORTANT: Make sure that lines representing wires connect to the components, NO GAPS
CIRCUIT DIAGRAM
CIRCUIT DIAGRAM
I highly recommend the CIRCUIT DIAGRAM website for drawing diagrams for use in notes, presentations and lab reports.
(But do practice pencil and ruler as you may need in exams)
Ideal and non-ideal ammeters and voltmeters
Ideal and non-ideal ammeters and voltmeters
Ammeters measure current at a point in a circuit. Voltmeters measure the potential difference between two points in a circuit. 'Traditional' analogue meters work by using the magnetic effects of electric current to turn a needle proportional to the potential difference or the current. Modern multimeters can be used as ammeters, voltmeters or other measuring devices.
Ammeters measure current at a point in the circuit - should be in series with the component. Ideal ammeter takes no energy from the circuit (zero resistance), non-ideal (real) ammeters have constant and very low resistance.
Voltmeters measure the energy converted (per unit charge) between two points in a circuit and be placed in parallel across the component(s). Ideal voltmeters have infinite resistance, non-ideal (real) voltmeters have constant and very high resistance.
Resources from textbooks
Resources from textbooks
Oxford Physics: pages 182 - 196
Hamper HL (2014): pages 233 - 235 for using ammeters and voltmeters
Relevant questions from Dot Point Physics (5 Electric currents)
Relevant questions from Dot Point Physics (5 Electric currents)
pages 255 - 263
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