```Hear The Light?Jane F Long                    McAuliffe Elementary                               1841 N. Springfield                               Chicago IL 60647                               (312) 534-4400Objectives:

The students will illustrate and describe a circuit which uses a tape
player, inductor, and flashlight to modulate a light beam.
The students will construct a flashlight transmitter using the materials
below.

Materials:

Modulated Laser from "Snack Book", 22 gauge wire, iron nails, flashlight
per group, two ear plugs per group, two alligator clips per group, batteries
and battery holders for two batteries and four batteries.

Strategy:

Step 1    A.  Introduce topic to class by recording your voice into tape                    recorder, then playing it back to students by way of the                    modulated laser.  (Teacher will have to construct this prior                    to this lesson.)                B.  Have tapes on hand with a variety of music from different                    cultural groups and play this music to class by way of                    modulated laser.                C.  Pass the tape recorder around and allow each student to say a                    few words into the recorder.  Play back to students by way of                    laser.                D.  Elicit questions and responses from students about what they                    are seeing, hearing, etc.      Step 2    A.  Explain the parts of the transmitter portion of the modulated                    laser by starting with the tape recorder.  Every student                    should be familiar with a tape recorder.                 B.  Next explain that a simple ear plug is used.  Be sure to                    explain that the ear piece has been cut off, the wires                    separated and the alligator clips attached.  Pause to make                    sure class is with you on each step.                C.  Next explain that the tape recorder is connected to a wire                    coil (induction coil).  Most students will not know why so                    you will come back to this part.                D.  Point out the flashlight which all students should also be                    familiar with.  Explain that we have interrupted the path                    between the batteries and bulb and rerouted the path through                    the induction coil.      Step 3    A.  Why do we need the tape recorder and flashlight connected to                    the induction coil?                B.  What have we recently studied that looks similar to this                    coil? (electromagnets)                C.  What did we learn about electromagnets and how did we make                    them?                D.  Suggest that if we make an electromagnet and change the                    voltage or current going into that electromagnet, we will                    also change the magnetic field.  Pass out nails, wire,                    battery holders and batteries to each group.  Each group will                    test how many paper clips can be picked up with two batteries                    attached.  Then test how many can be picked up with four                    batteries.  Did the magnetic field change?  (Yes, it got                    stronger)      Step 4    A.  Now that we see the magnetic field changes as the voltage                    changes, what is changing the voltage in the modulated laser?                     (the variation in the music or sound)  Since music is made up                    of different notes and each note is made up of a different                    number of vibrations, the varying vibrations create a varying                    push in current or voltage.  This varying voltage changes the                    magnetic field in the induction coil.  What exactly does this                            mean and why is this important for the working of this laser?                    (In an induction coil, each loop in the coil interacts with                    the magnetic fields produced by the other loops in the coil.                   A self induced voltage is produced as this magnetic field                    changes.  Demonstrate that voltage changes when the magnetic                   field changes by attaching a coil to a galvonometer and                     passing a magnet through the coil).                B.  The induction coil pushes the current towards the light bulb.                     Since the music is changing the voltage going to the                    induction coil, what must be happening to the light?  (It is                    also fluctuating or modulating)                C.  Go over the meaning of the two terms: induction coil and                    modulate.  Now say that what we have just described is the                    transmitter.  This transmitter transmits or sends a signal to                    somewhere else.      Step 5    A.  Hold up the solar cell and speaker/amplifier.  This is our                    receiver.  In other words it receives the signal that we are                    sending.  Does anyone have any ideas about how this receives                    the signal?  (Solar cell changes the light energy to                    electrical energy.  Since the light beam is modulating, the                    electrical impulses from the solar cell are also modulating.                   As we described earlier, this changing electrical impulse or                    changing voltage is going into our speaker and causing a                    vibration in this speaker which is equal to the vibrations                    from the music at the source.  So what happens?  We hear the                    music that originated in the tape recorder from the receiver                    across the room).      Step 6    A.  Each group will make the transmitter part of the modulated                    laser and test it on teachers equipment.  Have a contest on                    who can hear the signal from the furthest away. Performance Assessment:

Students will use the modulated laser they built as a guide and illustrate
the circuit involved in making this work.  They will then describe in detail how
the modulated laser works.

Rubric: 5 points:  Circuit is illustrated completely and accurately.  The explanation is            clear enough for anyone to follow the instructions and build a            modulated laser. 4 points:  Circuit is illustrated as above but explanation lacks clarity.3 points:  Circuit is illustrated but not labeled, and explanation lacks clarity            and details.2 points:  Circuit is not illustrated completely and explanation unclear.1 point:   Illustration and explanation lack details necessary to understand the                lesson completely. Multicultural Applications:

Have various tapes from different cultural backgrounds to play for the
students.  Also ask the students how this lesson can apply to our lives and our
future.  What are the future uses and applications of this type of communication
device?

Reference:

Doherty, Paul, The Exploratorium Science Snackbook, Exploratorium, 3601 Lyon Street, San Francisco, CA 94123, 1991.```