Description:

This task is designed to take students approximately 40-50 minutes to complete.

The activity portion is done in small groups of 4. The follow-up questions are completed individually by each student working alone.

Overall Task Content Area:

Physical Science

Specific Knowledge Areas:

Motions and Forces

Energy

Performance Expectations:

• conducting investigations
• using equipment
• gathering, organizing, and representing data
• formulating conclusions from investigational data
• applying scientific principles to develop explanations and solve new problems

National Science Education Standards:

8 B PS 3: Transfer of energy: Grades 5-8
3.4 Electrical circuits provide a means of transferring electrical energy when heat, light, sound, and chemical changes are produced.

4 B PS 3: Light, heat, electricity and magnetism: Grades K-4
3.3 Electricity in circuits can produce light, heat, sound, and magnetic effects. Electrical circuits require a complete loop through which an electrical current can pass.

(Use the "hot" link on the PALS home page to check the full text of related National Science Education Standards, if desired.)

National Council of Teachers of Mathematics:

MEAS2: Apply appropriate techniques, tools, and formulas to determine measurements:
Grades 6-8 k. select and apply techniques and tools to accurately find length, area, volume, and angle measures to appropriate levels of precision

PS2: Solve problems that arise in mathematics and in other contexts:
Grades 6-8

CNX1: Organize and consolidate their mathematical thinking through communication:
Grades 6-8

REP1: Create and use representations to organize, record, and communicate mathematical ideas:
Grades 6-8

General Instructions to the Teacher:

This task is designed to take students approximately 40-50 minutes to complete.

Students will be working in groups of 4 for the experiment/activity part of this exercise.

Students work together for up to 20 minutes. They are instructed to notify you when finished with the group work, and then to go on to the individual work beginning with question #1. If students are still working together 20 minutes after the testing begins, instruct them to cease their group work and begin individual work. At this point, they may no longer talk. Whether or not they are just beginning their individual work, remind students that they now have about 25 minutes to complete the individual activity.

Students should be ready to work as soon as the period begins. Group assignments should be made in advance. The materials should be set out at each lab station, if possible. A central supply area, if needed, should be easily accessible. All supplies should be clearly labeled.

Materials:

• Compass
• Empty box (bottom only)
• Empty toilet paper tube
• One length of 22 gauge insulated magnet wire marked "Galvanometer"
• One length of 22 gauge insulated magnet wire marked "Generator"
• Strong bar magnet with north pole marked "N"
• tape

Advance Preparation:

• Each student will need two wires- one will be for the "generator" and one will be for the "galvanometer"
  • To make these wires- cut lengths of 22 gauge insulated magnet wire (looks like plain copper wire) such that the wires are sufficiently long to make 50 turns around the box with 30 cm left over.
  • Attach alligator clips to both ends of each wire.
  • Label one wire "Galvanometer" and one wire "Generator" for each student.
• Label the North pole "N" on each bar magnet.
• The student will need a "box bottom" that is unassembled. If boxes are assembled- simply cut the side corners of each box so that sides can be positioned flat to the table.

Content Background:

The simple galvanometer is used to detect the presence of an electric current and to determine the amount of the current. When a magnet is moved into or out of the coils of wire that are wrapped around the tube, the changing magnetic field intensity inside the tube creates a voltage along the wire. Increasing the rate of change of the field's intensity (in this case moving the magnet more rapidly into or out of the magnet) or increasing the number of turns of wire around the tube will increase the voltage. The voltage inside the wire causes a current to flow inside the wire, so as the voltage gets higher, the current gets larger. The current produces a second magnetic field, some of which occupies the space containing the compass, so as the current gets larger, the second magnetic field gets more intense. The second magnetic field causes the compass's needle to be deflected, so as the second field gets more intense, the deflection of the needle gets larger. Therefore, when a student rapidly moves a magnet into or out of the tube, the deflection of the compass needle should be larger than when the magnet is moved slowly. Finally, the direction of the compass needle's deflection depends on which pole of the magnet is pointed toward the tube and on whether the magnet is moving into or out of the tube.

Safety:

• Be careful.
• Teachers and students should always exercise appropriate safety precautions and utilize appropriate laboratory safety procedures and equipment when working on science performance tasks.
• Be sure to keep magnetic sensitive items away from the magnets! E.g. digital watches and calculators.

Extensions/modifications:

• To expand and target the specific NCTM standard(s) to be measured, ask the students to use ratios to compare the amount of deflection of magnet movement.