Download Lab 4 (Unit 6)

Unit 6 Electromagnetic Induction Goals After successfully completing this lab, you will be able to: 1) determine the conditions under which a current can be induced in a coil that is not connected to a battery; 2) determine which physical quantities affect the magnitude of the induced current; 3) record data carefully and identify patterns; and 4) revise a rule when new observations are made. Statement about organization… One lab report should be submitted for each group (please, remember to include all names!). Lab reports should be roughly organized as follows: statement of purpose (or statement of research questions), hypotheses and predictions, experimental procedure, collected data, analysis of collected data and conclusions. Lab reports will be evaluated using rubrics that were carefully designed to assess scientific abilities. The rubrics that will be used to evaluate this lab report are included at the end of this document. Students are strongly encouraged to thoroughly read through these rubrics before beginning lab reports. Labs are designed to fill the entire three-­hour session. It is important that you work hard and complete as much as you can, but there is no penalty for failing to reach the “finish line.” Please work carefully and thoroughly, and be sure to leave time at the end of the session to prepare what you have completed for submission. In these laboratory activities, you will generate currents in order to observe magnetic interactions. As Prof. Mazur mentioned in class, large currents can cause significant damage to power supplies if too much current passes through them for too long; in some cases, wires will begin to melt and the power supply may even explode! Therefore, to limit the current flowing through wires in this lab, make sure you include a resistor and a switch in any current loop you connect to a voltage supply. Also, please remember to turn off voltage supplies when you are not using them. You will use galvanometers and voltage supplies in these activities. The galvanometer must never be placed in the same circuit as the voltage supply; they must be completely disconnected from one another. The galvanometer is extremely sensitive and will be instantly damaged if it is connected to the voltage supply in any way. I Observation experiment: Using a magnet to induce a current in a coil Available Equipment: neodymium magnets, a coiled wire, a galvanometer, connecting wires Lab 4-2
Your goal is to design as many experiments as possible to cause a current (also called ‘inducing a current’) in a coil of wire that is not connected to a battery. Even though these experiments are qualitative in nature, be specific and precise with what you do. a) First, decide how you would set-­‐up the experiment to detect if there is current in the coil. Hint: The galvanometer needle will deflect if a current flows through it. b) Draw a sketch for each experiment you perform. Briefly describe what you did. Indicate whether there was current induced in the coil or not. c) Develop a rule: Devise a preliminary rule that summarizes the list of conditions needed to induce a current in a coil. II Testing experiment: Does a coil behave like a magnet? Available Equipment: two coils, assorted connecting wires, a voltage source (with resistors and switch), a galvanometer In the previous lab you may have attempted to disprove the hypothesis that a coil of wire with current behaves like a bar magnet. Keep trying! Design experiments using this equipment to try to disprove this idea. Hint: Use your knowledge about the properties of magnets to induce current in a coil using a second coil instead of a magnet. a) Design as many experiments as you can (at least two) to test the idea. For each experiment: b) Describe your experimental procedure and include a labeled diagram c) Using the idea you are testing make a prediction of the outcome of the experiment. d) Conduct the experiment and record the outcome. e) Did the outcome match your prediction? What is your judgment about the idea? III Observation experiment: Inducing a current in a coil Available Equipment: 2 coils, a voltage source (with resistors and switch), connecting wires, a galvanometer One of the coils is connected to the voltage source, and the other is not. Your goal is to design an experiment to induce current in the coil that is not connected to the voltage source, without moving either coil. a) Describe your experimental procedure. Include a labeled diagram. b) Indicate whether there was current induced in the coil or not. c) Develop a rule: Revise the rule you devised in experiment I by devising a more general rule that summarizes the results of the observations from experiments I and III. Hint: Think about this rule in terms of the magnetic field. IV Observation experiment: Magnitude of induced current Available Equipment: neodymium magnets, coils with varying number of windings, a galvanometer, a voltage source (with resistors and switch) Lab 4-3
By now, you know how to use a magnet to induce a current in the coil. Your goal for this set of experiments is to devise a qualitative rule that relates the magnitude of induced current to the properties of the magnet, the motion of the magnet, and the properties and the orientation of the coil. a) Briefly describe each experiment using a sketch or words. b) Come up with as complete a list as possible of factors that affect the magnitude of the current induced in the coil. c) Summarize the factors that affect the magnitude of the induced current. Devise a qualitative rule (in words) that relates the magnitude of induced current to other factors. Hint: Think about this rule in terms of the magnetic field. V How does a galvanometer work? Available Equipment: A galvanometer a) Play with the galvanometer. b) Discuss how the galvanometer works with your group and with your TA. c) Is your understanding of a galvanometer work consistent now with your previous knowledge? If not, why? Why did we do this lab? Summarize your findings: • What are the conditions under which a current can be induced in a coil that is not connected to a battery? • What are the factors that affect the magnitude of the induced current? When several factors affect some physical quantity, what is the general strategy that you would use to determine the effect of each of them? For each item listed below, if your write-­‐up sa1sfies the descrip1on in the right column, you will earn a maximum of 3 points.
Scien&fic Ability
Is able to design a reliable experiment that inves&gates the phenomenon Adequate
The experiment might yield interes1ng pa3erns relevant to the inves1ga1on of the phenomenon. Is able to describe how to use available equipment to make measurements All chosen measurements can be made and all details of how it is done are clearly provided. Is able to devise an explana&on for an observed pa?ern A reasonable explana1on is made. Is able to make a reasonable predic&on based A correct predic1on is made that follows from on a hypothesis
the hypothesis and incorporates assump1ons. Is able to determine specifically the way in The effects of the assump1ons are determined which assump&ons might affect the predic&on and the assump1ons are validated. Is able to make a reasonable judgment about the hypothesis
A reasonable judgment is made and assump1ons are taken into account. Is able to communicate the details of an Diagrams and/or experimental procedure are experimental procedure clearly and completely clear and complete.
Is able to iden&fy sources of experimental uncertainty All experimental uncertain1es are correctly iden1fied.