Materials Included In Kit

Additional Materials Required

Safety Precautions

The materials used in this laboratory activity are considered nonhazardous. Wear chemical splash goggles whenever working with chemicals, heat or glassware. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. All materials may be reused or discard excess sodium chloride, plastic cups and plastic wrap in the regular trash according to Flinn Suggested Disposal Method #26a.

Lab Hints

• Enough materials are provided in this kit for 20 students working in groups of 4 or for 5 groups of students. This laboratory activity can reasonably be completed in one 50-minute class period. The prelaboratory assignment may be completed before coming to lab, and the worksheet may be completed the day after the lab.
• This laboratory experiment should not be used as a diagnostic tool. If hearing loss is suspected, please seek professional testing from an audiologist.
• This laboratory activity can easily accommodate more student groups with the purchase of additional tuning forks.
• More information about Noise Induced Hearing Loss (NIHL) is available at websites for the American Hearing Research Foundation, Kidshealth.org and Hearing Education and Awareness for Rockers (H.E.A.R.).

Teacher Tips

• Many students may be surprised by the ramifications of using MP3-type devices incorrectly. Often they believe if the device is capable of reaching a certain volume it must be safe to do so. By conducting this lab students will learn things they can do now to protect their hearing for life.

Answers to Prelab Questions

1. Describe tinnitus in your own words.

   Tinnitus is a condition in which the brain thinks it is hearing sounds that are not actually present.

2. How does smoking contribute to poor hearing?

   Smoking restricts blood flow. When blood flow is decreased the cilia are not able to repair, causing them to break. Cilia are broken permanently resulting in decreased hearing ability.

Sample Data

Answers to Questions

1. How do sound waves contribute to the changes observed in both water and salt when exposed to a tuning fork?

   Sound waves carry energy that creates an alternating pressure traveling through a solid, liquid or gas. The pressure from the waves caused the water and salt to be displaced.

2. In steps 12 and 13, plugging each ear was done to simulate conductive hearing loss. Did the test results turn out as anticipated?

   Most students will find that the sound was more prevalent in the plugged ear simulating conductive hearing loss.

3. 1. Based on your results of the Rinne test, did sound last longer when conducted through bone or air?

      The Rinne Test suggests that sound travels longer through air than bone.

   2. Was this consistent with anticipated results?

      Typically, this will be true in most students’ results.

4. How does sound differ from sound waves?

   Sound waves carry energy which causes alternating pressure due to differences in the density of molecules. Sound is similar to hearing. It is our interpretation of the amplitude, frequency and duration of the sound waves.

5. A vacuum is a space that is empty of matter. Is it possible to have sound in a vacuum?

   Sound is a mechanical wave created by the vibrations of material objects and therefore requires a medium in order to propagate. This means that for sound to travel, some type of matter (solid, liquid or gas) must be present. Matter is needed because sound travels by pushing molecules back and forth. If no molecules are present to push, such as in a vacuum, sound will not propagate.

6. Describe the specific modifications you can make to protect yourself from hearing loss.

   It is important when using MP3 players to not play them over half their volume capacity and it is also advised not to use them for more than one hour at a time. It is also beneficial to use ear plugs when performing loud activities such as using loud power tools.

References

American Speech-Language-Hearing Association. Type, Degree and Configuration of Hearing Loss. http://www.asha.org/public/hearing/disorders/types.htm (Accessed June 2010).

McDonnough, J. T.; Matkins, J. J. Using Sound Knowledge to Teach About Noise-Induced Hearing Loss. Science Scope. 2007, p 42–47.

Silverthorn, D. Human Physiology: An Integrated Approach; Pearson: Benjamin Cummings: San Francisco, CA; 2004; pp 341–342.

Introduction

Every day we are exposed to sounds from televisions, radios and even traffic. Usually these sounds are present at safe volumes that do not affect our hearing. However, when exposed to sounds that are too loud or that last too long, hearing can be damaged. Conduct this simulation to understand how sound waves affect structures similar to the human ear.

Concepts

• Sensory perception
• Hearing loss

Background

The ear is an organ that serves two distinct functions—hearing and equilibrium. Hearing is our perception of energy carried as sound waves. Sound waves are alternating pressure waves with peaks of compressed air and valleys of diffuse air. Sound is a person’s interpretation of the amplitude, frequency and duration of the sound waves (see Figure 1).

Sound is characterized by pitch and loudness. Pitch is interpreted as high and low sounds. Our brain interprets low-frequency waves with low-pitched sounds and high-frequency waves with high-pitched sounds. Loudness, which will be studied in this activity, is characterized by sound intensity and is also influenced by the sensitivity of an individual’s ear. The intensity of a sound wave is a function of the wave amplitude. Intensity is measured in decibels (dB) (see Figure 2). Normal conversation has a noise level of around 60 dB. At concerts the music is often projected around 120 dB. This intensity places listeners in danger of damage to their hearing. The amount of damage depends on the duration and frequency of the noise. Electronic music players such as iPods^® and other MP3 players are commonly used among teens. These electronic devices have the potential to produce noise levels that can cause damage to the ear. A recent study revealed that more than half the population of teenagers in the United States experienced ringing in their ears. Tinnitus is a condition characterized by the perception of ringing, buzzing, hissing and other noises, even in the absence of sounds. It can be caused by ear infections and as a result of noise-induced hearing damage.

In order to understand how hearing loss can occur it is important to understand the anatomy of the ear. The structures of the inner ear include delicate hairs called cilia. Cilia bend in response to pressure waves; this movement sends signals to the brain. Cilia bend and then can break when exposed to loud sounds (classified as sounds > 80 dB) especially if the noise is extremely loud or if it occurs over an extended period of time. Once cilia break, they cannot repair themselves. Resting the ears by avoiding loud sounds for extended periods of time allow the bent cilia in the ear to recover from the pressure created by the excessive noise.

Audiologists, professionals who diagnose and treat hearing loss, recommend limiting exposure to loud noises whenever possible. This includes turning down the volume of music players and decreasing the amount of continuous time exposed to them. Other methods of protecting hearing are earplugs, use of high-quality headphones, turning the volume down, resting ears between sessions and not smoking. Smoking restricts blood flow; therefore the cilia are not able to recover as quickly, causing breakage.

If an audiologist suspects hearing loss, the patient is given an audiometry test. In addition to a physical examination, the Weber and Rinne tests may also be performed to determine the type of hearing loss. Hearing loss is divided into two main categories— conductive and sensorineural. Conductive hearing loss occurs when sound is not conducted efficiently through the outer ear to the eardrum. It usually results in a reduction of sound level or the inability to hear quiet sounds. Sensorineural hearing loss occurs when there is damage to the inner ear or to the nerve pathways from the inner ear to the brain. This occurs as a result of being over-exposed to loud noises. Sensorineural hearing loss also involves a reduction in sound level, but also affects speech understanding, or ability to hear clearly.

Both the Weber and Rinne tests use a 512- or 1024-Hz tuning fork. During the Weber test a vibrating tuning fork is placed in the middle of the subject’s forehead. The sound will seem louder in the ear with conductive hearing loss. If the sound seems to be evenly distributed between both ears it may indicate proper hearing or symmetrical hearing loss (equal loss in both ears). The Rinne test is conducted in addition to the Weber test to determine if the hearing loss is sensorineural. The vibrating tuning fork is placed directly on the mastoid process (the back side of the ear) until sound is no longer heard. Then the fork is immediately moved to the outside of the ear. Subjects with normal hearing or sensorineural hearing loss will hear the sound longer through air than through bone. If the subject has conductive hearing loss, her or she hears the sound longer through bone than air.

Experiment Overview

Simulate the effect sound has on your ears using a tuning fork, water and sodium chloride.

Materials

Prelab Questions

1. Describe tinnitus in your own words.
2. How does smoking contribute to poor hearing?

Safety Precautions

The chemicals used in this lab are considered nonhazardous. Wear chemical splash goggles whenever working with chemicals, heat or glassware. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

1. Fill a plastic cup with tap water.
2. Strike the tuning fork against the rubber heel of a shoe.
3. Immediately place the tips of the tuning fork into the water.
4. Record observations on the worksheet.
5. Stretch enough plastic wrap to tightly cover the top of the cup containing water.
6. Sprinkle a small amount of sodium chloride on the top of the plastic wrap.
7. Strike the tuning fork against the rubber heel of a shoe.
8. Approach the top of the plastic wrap with the tuning fork. Record observations on the worksheet.

Weber Test

9. Strike the tuning fork against the heel of a rubber-soled shoe.
10. Hold the fork to the middle of the subject’s head as shown in Figure 3.
    {11018_Procedure_Figure_3}
11. Ask the subject which side the sound seems louder, if either. Record results on worksheet.
12. Repeat steps 9–11 while the subject plugs his or her left ear using a finger. Record results on worksheet.
13. Repeat steps 9–11 while the subject plugs his or her right ear using their finger. Record results on worksheet.

Rinne Test

14. Strike the tuning fork against the heel of a rubber-soled shoe.
15. Hold the tuning fork against the bone behing of the subject’s right ear as shown in Figure 4.
    {11018_Procedure_Figure_4}
16. Have the subject count how many seconds he or she hears the sound.
17. Repeat step 14 and hold the fork near the right ear as shown in Figure 5.
    {11018_Procedure_Figure_5}
18. Have the subject count how many seconds he or she hears the sound. Note which form of conduction lasted longer.
19. Complete the worksheet.

Student Worksheet PDF

11018_Student1.pdf