Introduction:
As a physics professor, one of the most interesting topics to teach is the properties of light and sound. Understanding the nature of light and sound waves is essential for comprehending many aspects of the science and technology behind them. In this article, we’ll look at the key concepts, equations and formulas, examples, and references for further learning.
Properties of Light:
Light is a type of electromagnetic radiation that can be described as a wave or a particle. Here are the key features of light:
- Speed: The speed of light, denoted as "c," is 299,792,458 m/s in vacuum and is considered to be the fastest possible speed.
- Wavelength and frequency: The wavelength, denoted as "λ," is the distance between two consecutive crests or troughs of a wave. Frequency, denoted as "f," is the number of waves per second, measured in hertz (Hz). The relationship between wavelength and frequency is λf=c.
- Refraction and reflection: Light can be refracted or bent when it passes through a medium with a different refractive index. Reflection occurs when light bounces off a surface, obeying the laws of reflection.
- Interference and diffraction: When two or more light waves meet, they can interfere with each other constructively or destructively. Diffraction occurs when light waves bend around an obstacle or pass through a narrow opening.
Properties of Sound:
Sound is a form of mechanical wave, which means it requires a medium to travel through. Here are the key features of sound:
- Speed: The speed of sound depends on the temperature, pressure, and humidity of the medium it travels through. In air at room temperature and standard pressure, sound travels at about 343 m/s.
- Wavelength and frequency: The wavelength of sound is the distance between two consecutive compressions or rarefactions of a wave. Its frequency is the number of vibrations per second and is measured in hertz (Hz). The relationship between wavelength and frequency is λv=c.
- Pitch and loudness: Pitch is a subjective measure of the frequency of sound, ranging from low (bass) to high (treble). Loudness is a measure of the intensity of sound, measured in decibels (dB).
- Reflection and diffraction: Sound waves can reflect off surfaces and diffract around obstacles, just like light waves.
Examples:
- Reflection of light: When you look in a mirror, you see a reflection of yourself because light bounces off the mirror’s surface and into your eyes.
- Refraction of light: When light passes through a prism, it refracts and makes a rainbow because each wavelength bends at a slightly different angle.
- Interference of light: In thin-film interference, light waves reflecting off the top and bottom surfaces of a thin film can interfere with each other and create colorful patterns.
- Echoes: When you shout in a large, empty room, you can hear an echo because sound waves reflect off the walls and bounce back to your ears.
- Doppler effect: When a siren on an ambulance passes you, the pitch of the siren seems to change because the frequency of the sound waves changes as the ambulance moves towards or away from you.
References:
- Halliday, D., Resnick, R., & Walker, J. (2013). Fundamentals of physics (10th ed.). John Wiley & Sons.
- Giancoli, D. C. (2014). Physics for scientists and engineers with modern physics (4th ed.). Pearson.
- Serway, R. A., & Jewett, J. W. (2018). Physics for scientists and engineers (10th ed.). Cengage Learning.
