Physipics Review Fames

THREE: WAVES

NOTE: These FREE Frames are samples of a much larger, and growing, collection. The samples here are not  an unbroken sequence. The complete set, with both FREE and NOT FREE Frames provides explanation without gaps. 

W2b

Syllabus / specification points:

• Waves carry energy by vibrations but without transfer of material outwards from the source.

• A material that allows waves to travel through it, or transmits the waves, is a medium.

• Waves may lose energy to the medium; the medium absorbs the energy. 

• The absorbed energy may become dissipated in the medium.

• Waves spread form the source and so the energy they carry becomes more spread out.

• Higher rate of transfer of energy is associated with higher amplitude of the wave.

making sound waves with particles of air

W4d

Syllabus / specification points:

• Sources of sound vibrate.

• The vibrations make the surrounding medium, such as air, also vibrate.

• Vibrations of the medium create a moving pattern of compressions (where particles are close together) and rarefactions (where particles are further apart).

• The moving pattern is a sound wave.

• The vibrations of the particles of the medium (such as air) are parallel to the direction of travel of the wave.


musical notes, frequencies and wavelengths

W4g

Syllabus / specification points:

• Different notes (or different pitches) have different frequencies.

• Sound waves travel at the same speed in the same medium.

• Lower frequency waves have longer wavelength; higher frequency waves have shorter waveength.

• The relationship between frequency and wavelength is inverse (meaning that when one increases the other decreases).


refraction, wavelength and colour

W9b

Syllabus / specification points:

• Refraction happens at boundaries between media, such as at air-glass and glass-air boundaries.

• Different colours have different wavelengths and frequencies.

• Red light has longer wavelength (and lower frequency); violet light has shorter wavelength (and higher frequency).

• At air-glass and glass-air boundaries, violet light is refracted by bigger angles than red light is.

• That splits ordinary light, white light, into a colour spectrum. The process is called dispersion of white light.

• Our sensations of colour are created from different wavelengths by our eyes and brains.


predicting frequency

W11e

Syllabus / specification points:

• Equations predict, and being able to predict is extremely useful.

• An equation is a statement that the left side of the ‘=‘ sign has the same value as the right side.

• For good (‘correct’) equations the previous point is true whether or not we know what the values are.

• Until we know values we can use letters.

• In the equation ‘c = f x L’, c is the speed of light, f is frequency, and L is wavelength. Often, people use the Greek letter λ (lambda) for wavelength.

• An equation is a statement of truth. We can get a new statement of truth when we change an equation AS LONG AS WE CHANGE BOTH SIDES IN THE SAME WAY.

• So we can change  ‘c = f x L’ by dividing both sides by L.

• In the new equation, the right side has multiplication and division by L. Those are opposite processes. So the right side can become simpler: just f.

• If two values are the same, it doesn’t matter which is on the left and which is on the right.

• f  has the same value as c divided by L. That’s an equation for predicting the value of frequency.


reflection of light by a plane (flat surface) mirror II

W13c

Syllabus / specification points:

• Your face reflects light. 

• Reflected light spreads out from every point on your face. That’s how we see you.

• If the light hits a mirror there is more reflection.

• A normal line, at 90° to the mirror surface, helps us to understand how a mirror makes an image.

• When light is reflected by the smooth surface of a mirror the angle of the arriving light (measured from the normal) is the same as the angle of the reflected light.

• After reflection by the mirror the light keeps on spreading out.

• It spreads out as if it were coming from a point behind the mirror. 

• The image of a point on your face is created at a point behind the mirror. That happens for every point on your face. 

• So you see yourself behind the mirror. But it’s not a real you. We call to a virtual image.


singing and sound signals: using microphones, amplifiers and speakers

W15c

Syllabus / specification points:

• Voices produce vibrations, which travel as sound waves.

• The sound waves can carry complicated patterns of change, that start with the voice.

• Sound waves produce increases and decreases of pressure of the air.

• These changes in pressure cause vibrations in a microphone.

• The microphone generates changes of electrical voltage. The electrical changes match the pattern of the sound waves.  A cable can transmit the changes as a ‘sound signal’. 

• An amplifier supplies energy to increase the amplitude of the electrical changes. It doesn’t change the pattern of changes in any other way. It doesn’t change the frequencies.

• The amplified sound signal cause vibrations of a speaker.

• The sound from the speaker matches the sound from the voice, but it’s louder.


water waves spreading from a source

List of completed Physipics Frames

Waves V2.0, October 2021


W1a        Waves move, energy moves

W1b        Waves with amplitude carry energy faster

W1c        Measuring water waves I: wave speed, amplitude, and wavelength

W1d        Wavelength and amplitude of some ocean waves

W1e        Measuring water waves II: introducing frequency

W1f         Frequency and period


W2a        Transmission, absorption and reflection of water surface waves

W2b        Water waves spreading from a source


W3a        Comparing reflection and refraction

W3b        Diffraction of water waves


W4a        What makes us think that sound travels as waves I?

W4b        What makes us think that sound travels as waves II?

W4c        Sources of sound, transmitting media, and some reflections

W4d        Making sound waves with particles of air

W4e        Comparing sound waves and water surface waves

W4f         Frequencies of some sound waves and water surface waves

W4g        Musical notes, frequencies and wavelengths


W5a        Vibrations and hearing

W5b        Infrasound, sound, and ultrasound 


W6a        The speed of sound

W6b        Equations, logically … using sonar I

W6c        Equations, logically … using sonar II

W6d        Measuring distance with sonar

W6e        Measuring distance and making images with ultrasound


W7a        Seismic vibrations and waves

W7b        Refraction of seismic waves, and shadow zones

W7c        P-waves and S-waves


W8a        What makes us think that light travels as waves?

W8b        Things can happen to waves

W8c        Sound and light waves – travel through media


W9a        Light has wavelength and frequency

W9b        Refraction, wavelength and colour

W9c        Filters – absorbing or transmitting different wavelengths

W9d        Absorption, reflection and the colours of surfaces


W10a    Something invisible – infrared radiation

W10b    More than you can see – ultraviolet radiation

W10c    Some different radiations, different wavelengths, same speed through space

W10d    The radio age: using radio waves and microwaves

W10e    Using invisible radiations, X-rays and gamma rays


W11a    The electromagnetic spectrum: wavelength and diffraction

W11b    The electromagnetic spectrum: experiencing some different wavelengths and frequencies, all at the speed of light

W11c    The electromagnetic spectrum: speed = frequency x wavelength

W11d    Changing equations – is it just kids’ play?

W11e    Predicting frequency

W11f     Predicting wavelength


W12a    Electromagnetic radiation: health and hazards

W12b    Journeys of electromagnetic radiation, including visible light

W12c    When light arrives at surfaces


W13a    Rays: reflection and refraction of light

W13b    Reflection of light by a plane (flat surface) mirror I

W13c    Reflection of light by a plane (flat surface) mirror II

W13d    Refraction by glass blocks

W13e    Total internal reflection (TIR)


W14a    Rays and images I

W14b    Rays and images II

W14c    Rays, images and lenses

W14d    The focal length of a converging lens

W14e    The image in your eye

W14f     Predictor rays and a converging lens I

W14g     Predictor rays and a converging lens II


W15a    Receiving information b y light and sound

W15b    Talking: varying frequency and amplitude to send information

W15c    Singing and sound signals: using microphones, amplifiers and speakers

W15d    Radio information

W15e    analogue to digital to analogue



















Copyright (c) David Brodie, 2019-2021

Photography: Adobe Stock

Copyright (c) David Brodie, 2019-2021

Photography: Adobe Stock