9u2.1 - Properties of waves

Certain forms of energy can travel from one place to another in the form of waves. The nature of the wave is determined by the medium in which it travels and the type of wave involved. However, all waves involve oscillation (moving to and fro about a fixed point) or vibrations of one form or another.

Characteristics of waves

• Frequency
• Wavelength
• Velocity
• Amplitude

Frequency

Waves can be described by their vibrations per unit time, called the frequency. The frequency of a wave is measured in Hertz, or cycles per second. The frequency is given the symbol f, or the Greek letter nu (ν). The number of complete waves passing a fixed point per unit time is the frequency.

Wavelength

The wavelength measures the distance between the same point of two consecutive waves. It is a distance and therefore measured in metres, m. The wavelength is assigned the symbol lowercase lambda, λ.

Velocity

The velocity or wavespeed is how fast the wave propagates from one place to another as m,easured by the displacement of the wavefront in metres per second. The wave velocity is assigned the symbol v, although for light it is asigned the symbol c.

Amplitude

The amplitude is a measure of the extent of each oscillation from the mid-point. It can be considered the height of the wave.

Wave calculations

The velocity of a wave, the frequency of the wave and the wavelength are related by a very simple equation:

Velocity = Frequency x Wavelength

Research and presentation

Research into animals which can make and detect waves for communication.

communication-in-animals

9u2.2 - Longitudinal and transverse waves

The vibrations of waves can either be perpendicular to the direction of wave motion or they can be in the same plane as the direction of wave motion. If the wave form is perpendicular to the direction of wave motion then the wave is said to be "transverse". If the vibrations act along the same line of wave propagation then the wave is said to be longitudinal.

Longitudinal waves are compression waves and include lengthways vibrations in springs and sound waves.

Transverse waves include water waves and light waves.

Caused by a vibration, particles vibrate back and forth, energy is transferred, compressions and rarefactions, air pressure increases and decreases to make the ear drum move.

9u2.3 - The ear and hearing

Sound waves

Sound waves are compression waves of the particles in the medium through which the energy is travelling. In air at 1 atmosphere pressure and 20°C, sound waves travel at about 343 ms^-1.

The more dense the medium in terms of particles the faster energy can travel through it. Sound travels through water at about 1500 ms^-1.

The source of the sound compresses the particles, leaving a region of rarifaction with fewer particles. The compression wave travels through the medium in this way.

The ear

Ears are the adaptation of organisms to use the vibrations of air particles (sound) to gain an evolutionary advantage. Prey animals can hear the approach of predators. Predators can detect the presence of the next meal.

Hearing

The vibrations travel through the air and are collected by the external ear structure, known as the pinna. These vibrations are then channelled into the middle ear through the ear canal, where they meet the tympanic membrane, otherwise known as the ear-drum. The vibrating air particles cause the ear-drum to vibrate and these vibrations are transferred by three small bones to the cochlear nerves, where the vibrations are changed to electrical signals that then travel to the brain for interpretation.

The effect of wave characteristics on sound

1. The wavelength of the sound

This changes the pitch that is heard. The shorter the wavelength the higher the pitch.

2. The amplitude of the wave.

The greater the amplitude the louder the sound

Sound in nature

There are very few creatures that have not adapted to make use of the information provided by vibrations in the air. Some organisms make far more use of sound than humans, particularly sea creatures, where the increased speed of sound in water can provide information very rapidly.

Sonar, echo location and even sound energy as a weapon.

Video link - Sound sense

9u2.4 - Electromagnetic radiation

Visible light

Light is a form of energy that propagates at 3 x 10⁸ ms^-1. The energy travels by vibrations of an electrical and magnetic field, called electromagnetic radiation.

The wavelength of visible light, i.e. radiation that can be detected by our eyes, is between 400 and 700nm (nanometres = 10^-9 m). The wavelength of 400nm corresponds to violet light, while the waves that have wavelength of 700nm corrspond to red light. All of the colours fall between these two wavelengths. This is known as the visible spectrum

The electromagnetic spectrum

Visible light makes up only a small fraction of the possible wavelengths of electromagnetic radiation. These waves can range from a tiny fraction of a nanometer to thousands of kilometers. The whole range is described by bands of radiation wavelengths, only one of which is visible light. The whole range is known as the electromagnetic spectrum.

9u2.5 - The law of reflection

Reflection

Imagine you're standing in front of a mirror holding a ball. When you throw the ball at the mirror, it bounces back to you. The law of reflection is like a rule that describes how this bouncing happens.

Here's the rule: When light (or in our example, the ball) hits a surface, like a mirror, it bounces off at the same angle it hit the surface. So, if you throw the ball straight at the mirror, it bounces straight back to you. If you throw it at an angle, it bounces off at that same angle.

So, the law of reflection is basically saying that when light hits a shiny surface, like a mirror, it bounces off in a predictable way. It's like playing billiards and knowing exactly where the ball will go after it hits the edge of the table.

The angle of incidence = the angle of reflection

9u2.6 - The pinhole camera

What is a Pinhole Camera?

Also called a camera obscura, A pinhole camera is a simple camera that uses a small hole to project an image onto a surface. This style of camera has been used for centuries and is a very simple way to explore photography.

How does a pinhole camera work

When light from a scene enters through a tiny hole (the “pinhole”) in the front of the camera, it forms a beam of light rays. These light rays travel in straight lines and create an upside-down image of the scene on the back wall of the camera (the tracing paper), which acts as the film or sensor. This happens because each point in the scene sends out rays in different directions, and the pinhole lets only a small set of rays from each point through to the back wall.

Watch on YouTube

9u2.7 - Refraction and lenses

Refraction

When a wave enters a new medium, the frequency stays the same but the wavelength, speed and direction can change. The change of direction is called refraction.

Lenses

Lenses make use of the refraction of light by changing its direction to that the light forms images on screens.

There are two types of lens, converging and diverging. The converging lens (convex) is the "fat" one and the diverging lens (concave) the "thin" one.

9u2.8 - Sight and the eye

Sense of Sight

The sense of sight, also known as vision, is one of our key senses. It allows us to perceive and interact with our surroundings, functioning primarily through the eyes.

Structure of the Eye

• Eyeball: The organ that contains all necessary components for sight.
• Cornea: The clear, dome-shaped surface that helps focus incoming light.
• Pupil: The opening in the center of the iris, controlling the amount of light that enters the eye.
• Iris: The colored part of the eye, adjusting the pupil size based on light levels.
• Lens: Focuses light onto the retina and adjusts shape for focusing at different distances.
• Retina: Contains photoreceptors that convert light into electrical signals.

How We See

• Capturing Light: Light is focused by the cornea and lens onto the retina.
• Image Processing: Light is detected by rods and cones in the retina and converted into electrical signals.
• Signal Transmission: Signals are transmitted to the brain via the optic nerve.
• Perception: The brain processes signals to produce visual perception.

Watch on YouTube

9u2.9 - Diseases of the eye

Common Vision Problems

• Myopia (Nearsightedness): Trouble seeing distant objects clearly.
• Hyperopia (Farsightedness): Trouble seeing close objects clearly.
• Astigmatism: Vision distortion caused by an irregular cornea.
• Color Blindness: Difficulty distinguishing certain colors.

Myopia

Myopia is also called short-sighted, or near-sighted. In this situation the person has difficulty focussing on far objects.

Hyperopia

This is also called hypermetropia, long-sighted or far-sighted. In this situation the person has difficulty focussing on near objects. This is typical of older people who's lens becomes less flexible and cannot be compressed to bring near objects into focus.

Importance of Eye Care

Maintaining eye health is crucial for clear vision. Regular eye exams, protective eyewear, and good nutrition can help preserve eye health.

Unit Test

Revision list

Subject-Specific Content to be Assessed (topic, knowledge and skills):

• • Longitudinal and transverse waves
• • Sound waves
• • Sound waves for communication in animals
• • The ear
• • Water waves
• • Light waves
• • The electromagnetic spectrum
• • Prisms
• • Reflection and refraction
• • Lenses
• • The eye
• • Problems with vision

Water and sound waves. The ripple tank. Water waves are transverse, sound waves are longitudinal. Wave equation

Diffraction and interference

Radiowaves, microwaves, infra-red, visible, ultra violet, X-ray, gamma, cosmic.

Symmetry extension

Design and construct in class

Different eyes from the animal kingdom. The brain does the processing - we do not "see" the image.

Myopia, hypermetropia, detached retina, glaucoma, cataracts - deficiency disease

No calculations

Resonance circus (Extension)

• 1. Pendulum on strings – amplitude – waves not resonance
• 2. Metal strips on motor
• 3. Tuning fork on giant tube
• 4. The sonometer – speaker/box/paper flies off
• 5. Video – tacoma bridge/ Video shattering glass with resonance