The magnetic effect of a current-carrying conductor

Transcription

1 Teacher's/Lecturer's Sheet The magnetic effect of a current-carrying conductor (Item No.: P ) Curricular Relevance Area of Expertise: Physik Education Level: Klasse 7-10 Topic: Elektrizitätslehre Subtopic: Elektromagnetismus Experiment: Die magnetische Wirkung eines stromdurchflossenen Leiters Difficulty Preparation Time Execution Time Recommended Group Size Intermediate 10 Minutes 10 Minutes 2 Students Additional Requirements: Experiment Variations: White paper (DIN A4) Ruler (approb. 30 cm) Keywords: Task and equipment Information for teachers Additional Information Whereas the heating and lighting effects of electric current are directly perceivable with human senses, this is not the case with the chemical and magnetic effects. In this ebperiment, the students should recognise that a current-carrying conductor is surrounded by a magnetic field. They will then be in a position to understand the functioning of common electrical appliances and equipment, such as electric bells and electric motors. For the ebplanation of the phenomena which occur during the ebperiment, it is helpful when the knowledge of the students on permanent magnetism (forces between magnets; magnetic poles; magnetic fields) is refreshed prior to this ebperiment. Notes on setup and procedure In this ebperiment, we are using de facto a short-circuit. This is permissible, because the power supply is equipped with an electronic current limitation. This should be pointed out to the students, because they could otherwise underestimate the dangers connected with short-circuits. Remarks As the connecting cables are made of copper, they cannot be related to the magnetic effect. The fact that we are dealing here with field lines which do not run in the direction of one pole to the other, and also do not pass into a body or emanate from it, is frequently surprising for the students and difficult for them to understand. The introductory ebperimental steps using a bar magnet in the second ebperiment are intended to reactivate the knowledge of the students on permanent magnets and so to make it easier for them to understand the most important analogies to electromagnets.

2 The mngnetic effect of n current-cnrrying conductor (Item No.: P ) Tnsk nnd equipment Tnsk Does electric current nlso exert mngnetic effects? 1. Use a compass needle to ebamine whether a straight conductor which is carrying current eberts a magnetic effect. 2. Demonstrate that a coil which carries current acts like a bar magnet, and ebamine on what the strength of its magnetic field is dependent.

3 Equipment Position No. Mnterinl Order No. Qunntity 1 Straight connector module, SB Angled connector module, SB Interrupted connector module, SB Junction module, SB On-off switch module, SB Coil, 400 turns Coil, 1600 turns Yoke Drawing compass, 2 units piece 10 Connecting cord, 32 A, 250 mm, red Connecting cord, 32 A, 250 mm, blue Connecting cord, 32 A, 500 mm, red Connecting cord, 32 A, 500 mm, blue Multi-range meter, analogue PHYWE power supply DC: V, 2 A / AC: 6 V, 12 V, 5 A Bar magnet, l = 72mm Additional material White paper (DIN A4) Ruler (approb. 30 cm) Set-up nnd procedure Set-up First experiment Set up the circuit as shown in Fig. 1 and Fig. 2. Plug a short connecting cable in the junction connector building blocks so that it lies along the North-South direction. Set the limiting current of the power supply to 2 A.

4 Fig. 1 Fig. 2 Second experiment Draw two lines at right angles to each other on the sheet of paper, then position the compass on it so that the pivot of the compass needle lies directly above the point of intersection of the lines. Turn the sheet of paper until the compass needle lies along the shorter line and mark the ends of this line N and S (see Fig. 4). Place the bar magnet on the sheet of paper at a distance of about 10 cm from the compass needle and mark two field lines on the paper (Fig. 3 and Fig. 4). Fig. 3 Fig. 4 Third experiment Set up the circuit as shown in Fig. 5 and Fig. 6, with the switch first open; connect the coil with 1600 turns between the two long connecting cables and select the 300 ma measurement range. Remove the bar magnet and replace it, in the same position, with the coil. Bring the compass back into its original position (above the intersection of the lines) and rearrange if necessary.

5 Fig. 5 Fig. 6 Procedure First experiment Set the power supply to 0 V and switch it on. Close the switch and increase the voltage until the control lamp on the power supply lights up. Open the switch and hold the compass directly under the connecting cord which lies North-South. Close the switch and observe the compass needle. Open and close the switch several times while observing the compass needle, and note what you observe under Result - Observation 1 in the report; in addition, make a sketch of the position of the compass needle relative to the straight conductor (+ ). With the switch closed, hold the compass directly over the straight conductor (connecting cord) and observe the compass needle as shown in Fig. 6. Note your observation under Result - Observation 2, and sketch the present position of the compass needle relative to the straight conductor. Lift the compass higher and higher and observe the deflection of the compass needle; hold the compass directly under the straight conductor and move it downwards while observing the compass needle; note your observations under Result - Observation 3. Hold the compass directly alongside the straight conductor, then slowly move it horizontally away from the straight conductor, while observing the compass needle. Note your observation under Result - Observation 4. Finally, again hold the compass under the straight conductor, open the switch, reverse the polarities of the power supply and ammeter connections, close the switch, observe the compass needle and note what you observe under Result - Observation 5. Set the power supply to 0 V and switch it off. Fig. 7 Second experiment

6 Move the compass slowly once around the bar magnet along the marked field lines, observing the movement of the compass needle. Note what you observe under Result - Observation 6. Third experiment Set the power supply to 0 V and switch it on. Close the switch. Increase the voltage until the ammeter shows 250 ma. Slowly approach the compass to the coil, observing the compass needle; note what you observe under Result - Observation 7. Move the compass slowly once around the coil along the marked field lines, observing the movement of the compass needle and comparing it with that noted under Result - Observation 6. Note your observation and the result of the comparison under Result - Observation 8. Bring the compass back into its original position. Note the deflection of the compass needle at successive current intensities of 250 ma, 150 ma and 50 ma; in each case suitably mark the position of the tip of the compass needle on the sheet of paper (e.g. with dots); note your observation under Result - Observation 9. Open the switch, set the power supply to 0 V and replace the coil with 1600 turns with the coil with 400 turns. Close the switch. Observe the deviation of the compass needle at 50 ma, 150 ma and 250 ma, and suitably mark each position of the tip of the compass needle on the sheet of paper (e.g. with dashes); compare the deflections with those caused by the coil with 1600 turns; note your observation under Result - Observation 10. Slide the iron core (yoke) in the coil; compare the deflection of the compass needle before and after sliding the iron core in; note the result under Result - Observation 11. Lay nails or paper clips on the sheet of paper and bring the coil with core near to them; note what you observe under Result - Observation 12. Set the power supply to 0 V and switch it off.

7 Report: The magnetic effect of a current-carrying conductor Result - Observation 1 (10 Punkte) Result - Sketch 1 (10 Punkte) Sketch the position of the compass needle as observed in Observation 1.

8 Result - Observation 2 (10 Punkte) Result - Sketch 2 (10 Punkte) Sketch the position of the compass needle.

9 Result - Observation 3 (10 Punkte) Result - Observation 4 (10 Punkte)

10 Result - Observation 5 (10 Punkte) Result - Observation 6 (10 Punkte)

11 Result - Observation 7 (10 Punkte) Result - Observation 8 (10 Punkte)

12 Result - Observation 9 (10 Punkte) Result - Observation 10 (10 Punkte)

13 Result - Observation 11 (10 Punkte) Result - Observation 12 (10 Punkte)

14 Evaluation - Question 1 (10 Punkte) Which conclusion must be drawn from the observations which you have noted under Observation 1, 2, 3 and 5? Evaluation - Question 2 (10 Punkte) The form of the magnetic field which apparently surrounds the straight conductor when this carries current can be determined from the observations noted under Observation 1, 2 and 4 as well as from the sketches. Try to describe this magnetic field (the course of the field lines).

15 Evaluation - Question 3 (10 Punkte) Below it is showed how the course of the field lines of a current-carrying conductor can be determined by the right hand rule. Try to ebplain this rule in your own words.

16 Evaluation - Question 4 (10 Punkte) What can be concluded from Observations 7 and 8 with respect to the effect of a coil which is carrying current? Evaluation - Question 5 (10 Punkte) What is the strength of the magnetic field of a coil which is carrying current dependent on? Ebpress this dependency as far as possible with The... the....

17 Evaluation - Question 6 (10 Punkte) A coil which is carrying current is called an electromagnet. Summarise the advantages, and any disadvantages, which an electromagnet offers when compared to a permanent magnet. Evaluation - Question 7 (10 Punkte) Give ebamples of practical uses of electromagnets.