What is the concept behind series connections
Introduction to electricity
Introduction of current and voltage
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By Mrs. H. Urban-Woldron (E-Mail) developed and made available from Vienna:
Applet on current strength, potential and voltage in the electric circuit for download: Electric circuit
Overview of the lesson:
In the proposed teaching concept, types of charge and electrons are initially dispensed with and the relatively neutral overarching term electricity is used. The sign difficulties caused by the negative electrons are thus avoided in the introductory phase. Energy considerations are only carried out later (in Bavaria in the 8th school year).
The magnetic effect around current-carrying conductors is particularly emphasized. It provides convincing arguments in favor of the circuit concept and against the consumption of electricity (even third graders can understand and apply the arguments!). The change in the magnetic effect when reversing the polarity (a motor changes its direction of rotation; a magnetic needle under a cable deflects in the other direction) is not compatible with a two-lead concept, but with a circuit concept. The latter is further reinforced by the observation that the deflection of two magnetic needles under the cables takes place in the same direction and is of the same magnitude, just in front of and behind a lamp. This can be interpreted in such a way that “the same thing is going on” in front of and behind the lamp in the supply lines, the electricity flows in the same direction and it flows the same amount. A qualitative measure of the current strength is provided by the change in the brightness of a lamp and the deflection of the magnetic needle in the same direction.
This is about the introduction of the current strength as a measure of the intensity of the process in an electrical device in a deeper and more precise manner. Even if the principle of the moving-coil measuring device can no longer be regarded as being up-to-date for a measuring instrument, it is didactically of great value for introduction. When a lamp and motor are connected in series, the brightness of the lamp serves as an indicator of the amount of electricity that is flowing through the lamp at any given point in time. The rotation of the motor is prevented by a spring dynamometer, the extension of which depends on the current strength (Caution: the current strength can easily exceed the permissible current strength when the motor is braked and the winding can burn out). This idea is related to the moving coil measuring instrument, in which the coil rotation is also braked by a spring.
After being informed that the unit of current strength is determined by the magnetic effect, the students carry out measurement exercises on series and parallel connections. The statements about the current strength in the unbranched circuit and the knot rule are formulated as a rule of thumb.
Without discussing the behavior of water circuits in detail, the analogy that a pump must generate a pressure difference between its input and output in order to push water through a circuit is used as an introduction to potential difference as a drive for the flow of electricity (references to hot water heating and water cooling for Car engine). Correspondingly, a battery generates a potential difference between its two connections in the sense of an electrical pressure difference on the electricity.
Using the rules for electrical potential described below: "The potential value at the positive pole of a battery or a power supply unit is greater than that at the negative pole" and "If two points are connected by a line, the potential has the same value at both points", can be used with With the help of this model, parallel, series and mixed circuits can be set up clearly and easily and the potential values and potential differences are illustrated. When lamps are connected in series, it becomes clear in an intuitive way that the potential difference given by the battery must be distributed among the lamps connected in series. With the parallel connection, you can easily work out that the same height difference, corresponding to the same potential difference, appears between the branching points.
|Rule (1)||The potential value at the plus pole of a generator is greater than at the minus pole.|
|Rule (2)||Outside of generators, electricity flows from places with a high potential value to places with a low potential value.|
|Rule (3)||If two points in a circuit are only connected by a connecting cable, the electrical potential has the same value at both points.|
|Rule (4)||Unless otherwise stated, the potential value at the negative pole of a generator is zero volts.|
In the following lesson, the term voltage is introduced for the potential difference and both terms are used synonymously over and over again. This makes it clear that a voltage always relates to two points.
In analogy to the pressure difference as a measure of the strength of a pump, the potential difference was introduced as the strength of a generator. Generators of different strengths lead to processes of different intensity in the same device, i.e. to different currents. This also gives rise to the idea for a measurement method: the effects are compared in a “standard device”. This can again be the force on a spring exerted by a motor braked by the spring. This brings you back to the principle of the moving-coil measuring mechanism (or as a black box, as is the case with current measurement with the current multiple measuring instruments). A convincing choice of the unit of measurement can best be justified later in connection with electrical energy or power.
This is followed by exercises in measuring tension.
|Rule (5)||The greater the voltage (potential difference) between the connections of the generator, the greater the current through the connected electrical device.|
In these lessons, potentials, voltages and currents are practiced in more complicated electrical circuits.
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