2 • Ultrasonics / Resonance / Beats / Velocity of Sound

Define the Audio Frequency Range of the human Ear

20Hz - 20,000Hz

Define the Audio Frequency Range of the Dog Ear

20Hz - 30,000Hz

Define Ultrasonic Frequency

Frequencies above 20,000Hz

Name a use of the Audio Frequency Range

Dog Whistle

Define 3 uses of Ultrasounds

1. Sonar - navigation at sea

2. Medical - breaking up kidney stones

3. Ultrasonic scanning - Pregnancies

Define Resonance

The transfer of energy between two bodies with the same natural frequency

Demonstrate resonance using pendelums

1. Disturb Pendulum B

2. Causes pendulum D to oscillate as they have the same frequency

Demonstrate resonance using tuning forks

1. Make Tuning Fork A to vibrate, place it on Sound Box A

2. Ball starts vibrating, hence Tuning Fork R is resonating

Name 3 uses of Resonance

1. Microwave Oven

2. Shop Security Tags

3. Stethoscope

Demonstrate the use of a Microwave Oven

1. Resonance occurs between microwave and food molecules

2. Food gets hots, not oven

Demonstrate the use of Shop Security Tags

Resonance activates the door transmitter alarm

Demonstrate the use of a Stethoscope

You can hear the heartbeat when you match the skins frequency with the heart through pressure

What are beats a result of?

The interference of sound waves

Name the types of interference

Sound waxing - constructive interference

Sound waning - destructive interference

Define the laws of beats

1. Number of beats per second = f2 - f1

2. If number of beats = 0, then f1 = f2

Label This Formula

Number of Beats per Second

f2 - frequency 2

f1 - frequency 1

Demonstrate the interference of sounds

1. Elastic band slows down fork vibrations

2. Both forks vibrating make a beat due to difference in frequencies

Name a use of the interference of sound

Piano