The alternating current generator (Item No.: P )

Transcription

1 Teacher's/Lecturer's Sheet The alternating current generator (Item No.: P ) Curricular Relevance Area of Expertise: Physik Education Level: Klasse 7-10 Topic: Elektrizitätslehre Subtopic: Elektromotor und Generator Experiment: Der Wechselstromgenerator Difficulty Preparation Time Execution Time Recommended Group Size Intermediate 10 Minutes 10 Minutes 2 Students Additional Requirements: Experiment Variations: Keywords: Task and equipment Information for teachers Additional information The students are already well acquainted with a simple alternating current generator, the dynamo on their bicycle, whose working principle is to be worked out in this experiment. Technically, inner pole machines are used to generate high alternating voltages. These are generators with stationary induction coils and rotating (electro)magnets. The very simple model which the students are to construct and experiment on is an inner pole machine. Notes on setup and procedure It must be ensured, that the coils are so connected that the alternating voltages generated do not cancel each other out. The model of the galvanometer is not suitable for the detection or recognition of alternating voltage, as the natural vibration of the pointer of this instrument is too weakly damped. When time must be saved, then the displacement of the pointer of the measuring instrument from the zero point should be performed earlier in the preparation for the experiment. Remarks Alternating current generators with permanent magnets are only used technically when relatively low performances suffice, e.g. with bicycle dynamos. In higher performance alternating current generators, the magnetic fields are generated by electromagnets, which receive their exciting current via sliding contacts and slip rings. The observation noted under Result - Observations 4 and the evaluation in Evaluation - Question 3 in the report are unnecessary for the understanding of the construction and functioning of an alternating current generator; they are of significance, however, for education on the proper, independent handling of measuring instruments in experiments with alternating current.

2 The alternating current generator (Item No.: P ) Task and equipment Task How can alternating current be generated? Assemble a simple model of an alternating cbrrent generator and Bse it to obtain a clear Bnderstanding of generating alternating cbrrent technically.

3 Equipment Position No. Material Order No. Quantity 1 JBnction modble, SB Socket modble for incandescent lamp E10, SB Coil, 400 tbrns Coil, 1600 tbrns U-core Rotating stem Bar magnet, l = 72mm Connecting cord, 32 A, 250 mm, red Connecting cord, 32 A, 250 mm, blbe Connecting cord, 32 A, 500 mm, red Yoke Filament lamps 4V/0.04A, E10, piece 13 MBlti-range meter, analogbe

4 Set-up and procedure Set-up Set Bp the experiment as shown in Fig. 1. TBrn the adjbsting screw at the back of the instrbment to move the pointer of the measbring instrbment away from the zero point, as far as possible to the right; select the 100 mv / 50 µa measbrement range. Screw the magnet tightly to the rotating stem. Position the magnet between the two coils so that the poles are each abobt 1 cm distant from the coils, as shown in Fig. 2. Fig. 1 Fig. 2

5 Procedure Rotate the magnet at different speeds and observe the measbring instrbment; note what yob observe Bnder ResBlt - Observations 1 in the report. Insert the I-core in one of the coils (see Fig. 3) and again rotate the magnet; observe the measbring instrbment; note what yob observe Bnder ResBlt - Observations 2. TBrn the magnet slowly and thereby observe how often the pointer of the measbring instrbment is deflected to the left and to the right dbring one complete revolbtion; note what yob observe Bnder ResBlt - Observations 3. Rotate the magnet as qbickly as possible and thereby observe the pointer of the measbring instrbment, compare this with the previobs deflections and note yobr resblt Bnder ResBlt - Observations 4. Replace the two coils with 400 tbrns with the single coil with 1600 tbrns and connect it to the measbring instrbment; slide the yoke in the coil and rotate the magnet alongside to it (Fig. 4), compare the pointer deflection with that fobnd in ResBlt - Observation 2, note the resblt Bnder ResBlt - Observations 5. Fit the coil with 1600 tbrns on the U-core; connect the lamp holder with 4 V / 0.04 A filament lamp to the coil; insert the thin end of the rotating stem with magnet in the U-core (Fig. 5, Fig. 6), selecting a distance of abobt 5 mm between the magnet and the U-core; rotate the magnet very qbickly, observe the lamp and note yobr observation Bnder ResBlt - Observations 6. Fig. 4 Fig. 3 Fig. 5 Fig. 6

6 Report: The alternating hurrent generator Result - Observations 1 (10 Punkte) Result - Observations 2 (10 Punkte)

7 Result - Observations 3 (10 Punkte) Result - Observations 4 (10 Punkte)

8 Result - Observations 5 (10 Punkte) Result - Observations 6 (10 Punkte)

9 Evaluation - Question 1 (10 Punkte) What can be concluded from the observation, that the pointer of the measuring instrument swings to and past the zero point during the rotation of the magnet? Evaluation - Question 2 (10 Punkte) Explain the observation noted under Result - Observations 2.

10 Evaluation - Question 3 (10 Punkte) Explain the observation noted under Result - Observations 4 and then state the reason why an instrument designed to measure direct current (or direct voltage) cannot be used for measurements in an alternating current circuit. Evaluation - Question 4 (10 Punkte) Explain the observation noted under Result - Observations 5.