Electric Steel Guitar Lesson Plan

Transcription

1 Electric Steel Guitar Lesson Plan Science Standards Addressed: New Colorado P- 12 Academic Standards o 1. Physical Science - Apply an understanding that energy exists in various forms, and its transformation and conservation occur in processes that are predictable and measurable Adams County School District 50 Standards Based Education o SC Energy comes in many forms such as light, heat, sound, magnetic, chemical, and electrical (CAS: 4.1.1) o SC Recognize that waves such as electromagnetic, sound, seismic, and water have common characteristics and unique properties (CAS: 8.1.4) Objective: To explore the principles of electromagnetism and induction using a handmade electric steel guitar as a demonstration. Materials: Handmade electric steel guitar Amplifier ¼ instrument cable Tuning Fork (optional) Rubber band (optional) Electric guitars cover a wide range of scientific concepts meaning that creating corresponding lesson plans for the subject can be difficult. Therefore, we have decided to create a basic lesson plan that most students can understand and in addition, we have lesson plan extensions that we can dip into if the students appear interested and capable of understanding the material.

2 Basic Steel Guitar Lesson Plan: 1. Set up the guitar beforehand 2. Ask the students to describe what sound is, and how they think it works to get a sense of the knowledge base. 3. Introduce the term sound wave and play a few notes on the guitar to demonstrate. 4. Briefly explain the way that the sound wave propagates through the air. 5. Use the amplifier to alter the volume of the sounds. Students should be able to easily identify volume as a characteristic of sound. Establish that volume is related to amplitude of the sound wave. Draw samples of large and small amplitude waves on the board and ask students to predict which one is louder. 6. Produce sounds of varying frequency and see if the students pick up on the difference. If necessary, use guiding questions and visuals (i.e. Draw a high and low frequency wave and ask students to spot the differences ) 7. Establish that frequency is another characteristic of sound (and more generally, all waves). Demonstrate the concept of frequency with active participation from the students (ex: have them jump in place a certain number of times in ten seconds). Establish that frequency is the number of repetitions in a particular time period. 8. For a post survey, ask students to identify and separate low frequency sounds from high frequency sounds, and low amplitude sounds from high amplitude sounds.

3 Extensions to Basic Steel Guitar Lesson Plan Faraday s Law 101: 1. Electromotive Force (EMF) is generated in a closed circuit when the magnetic flux within the circuit changes at a certain rate (i.e. EMF generated is proportional to the rate of change of magnetic flux) 2. EMF is basically voltage. Magnetic flux can be taught to the students as the number of magnetic field lines going through the plane of the circuit. 3. Pickups have lots of loops so as to gobble up more magnetic flux! 4. Direction/orientation of flux are important in Faraday s Law. Faraday s favorite buddy, Lenz, has his own law, which talks about the direction. This is why orientation of pickups during humbucking works! 1. Describe the differences and similarities between the sound waves produced by the loudspeaker and those produced by the unamplified string. Answer: The primary similarity is that the two sound waves have the same frequency. The primary difference is that the amplitude of the sound wave from the speaker is larger than that of the vibrating string. 2. Trace the energy in the system, from the vibrating string to the sound that you hear from the loudspeaker. Make a flowchart illustrating the type of energy involved and the additions/transformations it goes through as it moves through the system. Neglect minor losses such as friction. Answer: A flowchart tracing the energy should show the kinetic energy of the vibrating string being converted to electromagnetic energy in the form of an alternating (AC) current by the pickup and traveling through the instrument cable. The amplifier adds electromagnetic energy by amplifying the signal, and this energy is converted back to kinetic energy by the vibrating loudspeaker.

4 Optional Steel Guitar Activity: Other Signals Note: This activity may or may not work as described depending on the pickup/amplifier used. Try it beforehand. 1. Plug in the guitar to the amplifier and turn the volume up to a moderate volume. 2. Rather than pluck the strings with a pick, hold the guitar close to your face and yell or sing into the pickups. You should hear your voice through the amplifier. If not, try turning up the volume until you can hear your voice. 3. Now, remove the pickup from the guitar and repeat. This time, you should not be able to hear your voice through the loudspeaker. 4. Take the tuning fork and hit it on your knee to get it vibrating. Slowly bring it closer to the pickup until you can hear it amplified in the loudspeaker. Caution: Do not bring the tuning fork too close to the pickup, or the magnets within may violently attract the tuning fork to the pickup, slamming them together and possibly causing damage!!! 5. Now, stretch out the rubber band such that you can pluck the band and generate a noticeable tone. While plucking the band, slowly bring it closer to the pickup. You should not hear the rubber band tone through the loudspeaker. 1. Why are you able to hear your voice through the loudspeaker when the pickup is installed in the guitar but not when the pickup is removed? Answer: The pickups operate by perturbations in the magnetic field surrounding the coils creating an alternating current in the wire due to electromagnetic induction. Vibrating guitar strings nearby will do this because they are made with nickel and iron and interact with magnetic fields. When the pickup is installed in the guitar, a loud enough sound close to the strings will cause them to vibrate at the same frequency, which is then amplified by the pickup/amplifier system. So, it is actually still the vibration of the ferrous strings causing the sound in the speaker, and not your voice directly. Microphones work in a similar way. 2. Why does the tuning fork generate a sound through the loudspeaker but the rubber band does not? Answer: The tuning fork is made out of some ferromagnetic alloy containing iron or nickel and interacts with the magnetic field of the pickup similarly to the guitar string. Therefore, its vibration is detected by the pickup and amplified. The rubber band is not made of a ferromagnetic material and therefore has no effect on the guitar pickup.

5 Advanced Activity: Humbucking Note: This activity requires the use of two pickups. Also, noise levels will vary depending on environment. Try this activity beforehand in the room in where the lesson will take place to get an idea of the relative noise levels present. You may want to experiment with location and orientation of the pickups. Think of them as antennas on an old FM radio. 1. Remove the two pickups from the guitar and connect them in series through the amplifier. 2. Hold the two pickups next to each other such that the North poles of the magnets within both point in the same direction. 3. Turn on the amplifier and turn it up to a high volume until you can hear a hum coming through the loudspeaker. 4. Now, rotate one of the pickups 180 degrees so that the North poles of the magnets within point in opposite directions. The hum sound should be reduced in this orientation. 1. Why is the hum reduced when the pickup orientation is reversed? Answer: The hum generated by the pickup is a due to the presence of electromagnetic noise in the room generated by electrical devices plugged into wall outlets. Since these devices are powered by alternating current with a frequency of 60 Hz, this noise has a frequency and by electromagnet induction generates a response in the pickup. If there are two pickups wired in series and placed next to each other, the signal generated in both of them is of the same amplitude and the hum will be twice as loud as if there were only one pickup. However, if we reverse the polarity of one of the pickups by turning it around, the signal generated by the noise of the room (which has not changed orientation) in that pickup will be exactly out of phase with the signal in the other pickup, and the two signals cancel each other, thus bucking the hum.