The construction of a speaker will be worth 5% of your term work (70%). The construction of a simple electric motor assignment will be worth 5% of your Culminating Evaluation (30%).
Each student must submit their own motor/speaker. These motors/speakers will be kept in the class until the end of the semester. A digital photo will be taken of the motor/speaker to avoid duplication.
Examples of the motor/speaker can be found in the physic classroom.
Cost - $0.00
Students should not to spend any money on parts. Wire is available from the school. Students are encouraged to be resourceful by taking scrap materials that are headed for the garbage.
Specifics on Motors
The motor is to be a model of the St. Louis Motor (shown on the next page), not a “Beakman’s motor”. Students can find other types of motors on the internet which are too easy to construct and do not require the understanding of the mechanics of motors or the underlying electromagnetic principles. Students are encouraged to use permanent magnets as the external magnetic source. You do not have to purchase magnets. Classroom magnets can be used during the test.
Specifics on Speakers
A speaker is much easier to build then a motor. However, the specifications on speakers are difficult to match for your home audio systems. Please do not test your speakers at home – it could damage your home audio systems.
Rubric for Motor and Speaker assignmentsCriteria / Below level 1
0-50% / Level 1
50-60% / Level 2
60-70% / Level 3
70-80% / Level 4
80-100% / % of final mark
Works / Not assembled / Requires significant modifications before it will work / Assembled to some resemblance of a working motor/speaker / Works with a minimal degree of teacher manipulation / Works quite well with little adjustment required by the teacher (speaker needs to be heard without bending over) / /40
Materials / rebuilt from an old speaker or motor / Uses many parts of old speakers and motors / Contains a few parts from old speakers and motors / Very little use of new material / Uses completely recycled items. / /40
Creativity / No imagination / Little imagination used in the construction / Some imagination used in the construction / Well designed / Imaginative and well designed / /20
Due Date: Last week of classesClosure Date: end of semester
St. Louis MotorExample of a St. Louis Motor Key Parts / Description of key parts
/ Place to input the current
Brushes must gently touch the commutator (split ring)
Axel should rotate freely. Armature should be properly balanced. Decide if you want the axel on a vertical or horizontal plane
Commutator should be made from a good conducting material. Check with a battery – many metals are coated.
Permanent magnets will be provided
Electromagnet – review the factors affecting the strength of an electromagnet covered in class.
The biggest mistake made in past is the proper wrapping of an electromagnet. Check the polarities once your electromagnet is constructed before continuing.
SpeakerCross-section of a speaker and its key parts / Description of key parts
/ Diaphragm (cone)– some sort of light weight material which will push the air as the speaker vibrates
Voice coil – the electromagnet which receives the continually changing current. The voice coil should be as light as possible without sacrificing its magnetic strength
Spider – an elastic material which supports the vibration of the voice coil and diaphragm – either attached to the diaphragm or voice coil
Magnet – a permanent magnet will interact with the electromagnet to facilitate the vibration
Note – F = ma, Newton’s second law is a major consideration in the construction of a speaker. To work properly, the voice coil must have a high rate of acceleration. Therefore, a large magnetic force (interaction between the permanent magnet and the electromagnet) coupled with a small mass (voice coil) will provide the best rates of acceleration.