Download Speaker in a Cup

Curriculum topics:
 Electricity
 Magnetism
 Electromagnetism
 Experimental
Variables
Subject:
Physical Science
SPEAKER IN A CUP
Change electromagnetic waves to sound waves
large nut
magnet
small nut
Grade range: 4 – 12
cup
washer
machine
screw
magnetic
strips
Get music out of a plastic cup! Create a working speaker by combining
a cup, lid, magnet, washer, nuts, and a machine screw with a coil of
magnet wire. The activity can be done as a step-by-step assembly or as
a Design Challenge.
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Teaching (RAFT) helps
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through affordable
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and inspire the joy and
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© 2015, RAFT
http://www.raft.net/raft-idea?isid=687
Materials required
Safety tip: Wash hands after
handling electrical components.
For each Speaker:
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Spoon straw
Double stick tape, ~3 cm x 1 cm (1”x ½”)
Magnet wire, 28 gauge, 1.5 m (60”) long
Sandpaper, fine grit, ~2 cm x 5 cm (1” by 2”)
Adhesive magnet strips, 1 cm x 2 cm
(3/8” x 1”), 2
Clear cup, ~270 ml (9 oz), with a lid with
straw slits
Ring magnet, ~2.9 cm (1⅛”) diameter with a
~1 cm (3/8”) hole
Machine screw, flat head, M5 - .8 x 20 (#832), ~2 cm (¾”) long, zinc coated
Matching size nut for machine screw,
M5 - .8 (#8-32)
Nut, large, M12 ~1.3 cm (½”), zinc coated
How to build it
1
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Steel fender washer, M5 - 25, ~3 cm (1¼”)
diameter with ~5 mm (3/16”) hole, zinc
coated
Cone shaped drinking cup, paper
Adapter (see Expanded Materials
Preparation & Assembly Guide at
http://www.raft.net/raft-idea?isid=687)
Sound source with earphone jack
Scissors
Warning! Use a low cost/ expendable
sound source! The speaker in a cup has
very low resistance and may damage
sound source.
Note: Some students may need assistance with the How to build it
steps. If needed, steps could be done in advance by an adult.
Wrap a strip of double stick tape around the sipping end of the spoon straw about ¼ cm (1/8”)
from the end of the straw as shown. Cut a slit into the spoon end of the straw as shown.
Cut small slit in the spoon end of the straw
Double stick tape wrapped around sipping end of straw
2
Fold the sandpaper over the end of the magnet wire and lightly sand away the insulated coating
from a 3 cm (~1”) long section until a bright copper color is just seen.
Note: When handling wire work slowly and carefully to avoid kinks.
3
Insert the sanded end of the magnet wire into the slit in the spoon straw. Run the magnet wire
down to the “sipping end” of the straw, see below.
Second run wire down straw
4
First insert wire into slit
Carefully coil the wire on top of the double stick tape. Make a neat coil about 1 cm (3/8”) wide,
overlapping back and forth as needed. Pull the wire fairly tight against the straw while wrapping,
straightening out any minor kinks that may have formed. Continue coiling until the wire left
uncoiled has a length equal to the length of the straw, as shown below.
Wire coil over
double stick tape
5
Remove the magnet wire from the slit and twist the 2 straight wires around each other 2 times,
very close to the coil to prevent the coil from uncoiling. Sand the other wire end as in step 2.
6
Cut the tip off the paper cone cup so as to create a hole a little smaller than the straw’s diameter.
7
Attach the adhesive magnet strips to the inside bottom of the cup, parallel, 1 cm (⅜”) apart. (See
Expanded Materials Preparation & Assembly Guide at http://www.raft.net/raft-idea?isid=687)
Speaker in a Cup, page 2
© 2015, RAFT
To do and notice
Check that the sound source is able to produce loud sounds.
For a radio-tune to a strong signal.
1
2
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paper cone
with tip cut off
Connect each of the adapter’s two clips to a sanded end of the coil’s wire.
Plug in the adapter into the sound source’s earphone jack.
cup lid
Basic Exploration
3
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Assemble the washer, machine screw, small nut and ring magnet as
shown below. Place the large nut on top.
large nut
small nut
magnet
machine screw
washer
4
spoon
Place the assembly from step 3 onto the magnet strips in the cup.
straw
Carefully insert the coil of wire into the magnet’s hole over the end of the
screw. Turn on the sound source and adjust the coil up & down; listen.
5
Pinch the spoon end of the straw and insert into the hole in the cup lid
from the cup side. Slide the lid down the straw and snap the lid onto
the cup. Place an ear near the cup lid, adjust the straw up & down; listen.
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Insert the spoon end of the straw into the hole in the paper cone from the
outside of the cone. Slide the cone part way down the straw. See the
illustration on first page. Adjust the coil of wire up & down, listen.
6
coil
large nut
In-depth Exploration
magnet
Explore the purpose of each of the parts. Compare the sounds produced small nut
by repeating steps 4-6 above for each of the following arrangements:
washer
machine screw
machine screw
small nut
inside magnet
(not visible)
cup
magnet
magnet
(only)
washer
add washer,
screw & small nut
large nut
added
magnetic
strips
The science behind the activity
For background information on electrons, magnetism, and sound see Expanded Science Behind the
Activity at http://www.raft.net/raft-idea?isid=687
Electromagnetism and Electrical to Kinetic Conversions
(Bolded words in parentheses are the proper scientific terms.)
Electrons can be made to bump along a path of metal wire (a conductive path) due to the push/pull
forces (voltage) created by a voltage source such as a battery. A sound source, such as a radio or MP3
player, will vary the flow of electrons (the current) in a way that duplicates the variations in sounds such
as speech and music.
Speaker in a Cup, page 3
© 2015, RAFT
Curriculum
Standards:
Energy can be
transferred from place
to place and converted
between forms
(Next Generation
Science Standards:
Physical Science,
Grade 4, 3-2 & 3-4;
High School, 3-3)
Waves
(Next Generation
Science Standards:
Grade 4, Physical
Science 4-1)
Electric or magnetic
interactions between
objects not in contact
(Next Generation
Science Standards:
Middle School,
Physical Science 2-5 )
Magnetic forces
(Next Generation
Science Standards:
Middle School, Physical
Science 2-3)
Electric Current Creates
a Magnetic Field
(Next Generation
Science Standards:
High School,
Physical Science 2-5)
Compare Multiple
solutions/Test Variables
(Next Generation
Science Standards:
Engineering Design,
Grades 3-5, 1-3; Middle
School, 1-2 &1-4; High
School, 1-3)
Break down complex
real-world problems
(Next Generation
Science Standards:
Engineering Design,
High School, 1-2)
Science & Engineering
Practices
(Next Generation
Science Standards:
Grades 4 – 12)
Additional standards at:
http://www.raft.net/raftidea?isid=687
Speaker in a Cup, page 4
The science behind the activity (continued)
For an electrical speaker to produce sound the electrical energy in the wire
must be converted into pressure waves in the air.
Electrons moving in a wire will create a temporary magnetic field around the
wire. That field will exist as long as the electrons flow. Changes in the direction
of the electron flow will change the orientation of the magnetic field. The
magnetic fields of the loops in the coil overlap creating a stronger magnetic field
(an electromagnet).
The large nut, washer, and screw concentrate the magnetic field of the
permanent magnet closer to the coil. This assembly will produce a louder
sound than the magnet alone.
concentrated
magnetic field
large nut
small nut
screw
magnet
washer
An electromagnet and permanent magnet which are near each other will be
either repelled when the like poles of the two magnets are closer together or
attracted when unlike poles are closer. The force of the attraction and
repulsion will vary with the variation of the electron flow. In Speaker in a Cup,
the magnet is fixed and the coil moves. When connected to the sound source
the coil’s tiny vibrations are transmitted to the straw, lid, and cone. The larger
surface area of the cup lid and cone will move more air, creating a
larger pressure wave and thus amplifying the sound.
Thomas Edison similarly used a large cone to enhance and direct
the sound from his first phonographic devices in 1877.
Learn more
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N
Connect the coil of wire, very briefly, to a battery, creating a magnetic
field (with poles at the coil’s ends) that can move a compass needle.
Compare with a simple coil of wire speaker – see Resources below.
Have a design challenge to create the loudest speaker.
Related activities: See RAFT Idea Sheet:
Breadboard Circuits - http://www.raft.net/ideas/Breadboard Circuits.pdf
Resources
Visit www.raft.net/raft-idea?isid=687 for “how-to” video demos & more ideas!
See these websites for more information on the following topics:
 Simple coil of wire speaker - http://madlabs.info/simple_speaker.shtml
 Basic information on electromagnetism http://www.allaboutcircuits.com/vol_1/chpt_14/2.html
 Student worksheet on electromagnetism http://www.allaboutcircuits.com/worksheets/em1.html
 Magnetic field lines for a speaker –
http://hyperphysics.phy-astr.gsu.edu/hbase/audio/spk.html
Acknowledgements:
Based on design by John Krupczak further developed by Kate Disney.
© 2015, RAFT