Unit 2 - Keep in touch (Physical Science extension)
Content
- 9PSu2.1 - Speed of sound
- 9PSu2.2 - Echo location
- 9PSu2.3 - Graphical representation of waves
- 9PSu2.4 - Waves, constructive and destructive interference
- 9PSu2.5 - Lenses and ray-diagrams
- 9PSu2.6 - Sub-structure of the eye, rods, cones, electromagnetic sensitivity
- 9PSu2.7 - Colour and perception
- 9PSu2.8 - Optical illusions
- 9PSu2.9 - Digital and audio information transmission - binary logic
Skills and understanding
Teaching notes and resources
Scheme of work
Virtual oscilloscope
9PSu2.1 - Speed of sound
Sound travels in compression waves. These are longitudinal and the energy transfer speed depends on the number of particles per unit volume, as well as the forces holding the particles together.
For this reason, the speed of sound in air is much lower than the speed of sound in water.
- Speed of sound in air =
- Speed of sound in water =
- Speed of sound in rock =
9PSu2.2 - Echo location
This is the process of sending out a sound wave and registering it when it boundes back off objects. Humans can hear echoes if the sound is loud enough and the distance is great enough, but there are many animals that use this effect located their prey or simply to build up an image of the surroundings in darkness.
The video "Sound Sense" shows how the animal kingdom has evolved to use sound in many ways.
Experiment to determine the speed of sound in air
A sharp short noise is made at one end of a 1m tube and the reflected sound detected using computer software.
The data is recorded 5 times and an average taken.
Factors affecting the speed of sound in air include anything that also affects the density of the air, such as temperature, atmospheric pressure and humidity.
9PSu2.3 - Graphical representation of waves
9PSu2.4 - Waves, constructive and destructive interference
Constructive interference occurs when two waves overlap and combine to create a larger wave by aligning their crests, while destructive interference happens when two waves overlap and partially or completely cancel each other out by aligning a crest of one wave with a trough of the other, resulting in a smaller wave or no wave at all.
Experiment: Interference patterns in a ripple tank
9PSu2.5 - Lenses and ray-diagrams
A lens is a shaped piece of transparent glass or plastic that refracts light. When light is refracted it changes direction due to the change in density as it moves from air into glass or plastic. Lenses are used in cameras, telescopes, binoculars, microscopes and corrective glasses. A lens can be convex or concave.
Convex lenses
A convex lens is thicker in the middle than it is at the edges. Parallel light rays that enter the lens converge. They come together at a point called the principal focus.
Convex lenses bulge outwards while concave lenses bulge inwards.
Concave lenses
A concave lens is thinner in the middle than it is at the edges. This causes parallel rays to diverge. They separate but appear to come from a principle focus on the other side of the lens.
The images formed by both types of lens is determined by the position of the object.
Glossary
- Object
- Real image
- Virtual image
- Inverted
- Focal length
9PSu2.6 - Sub-structure of the eye, rods, cones, electromagnetic sensitivity
9PSu2.7 - Colour and perception
9PSu2.8 - Optical illusions
9PSu2.9 - Digital and audio information transmission - binary logic