LIGHT AND SOUND YEAR 9 SCIENCE

Electromagnetic Spectrum Definition: a scale which classifies different types of light based on the distance of their wavelength. Short wavelength = high energy Long wavelength = low energy

Electromagnetic Spectrum

The Human Eye Cornea – a transparent layer at the front of the eye for protection. Iris – the coloured part of the eye, a ring of muscle that changes the size of the pupil Lens – angles and focuses light that enters through the pupil onto the retina. Retina – back layer of the eye, detects light that enters the eye because it contains light-sensitive cells called rods and cones. Fovea – a small pit in the retina, composed of lots of closely packed cone cells, providing the spot with the clearest vision. Optic nerve – sends information about light from the retina to the brain.

How We See Light Light enters the eye through the transparent cornea. Iris changes in size, allowing control over the amount of light entering the eye. Light passes through the pupil and the lens. Lens causes light to become focused in one point on the retina. Light is detected by rods and cones in the retina. Rods and cones send information to the brain about the light via the optic nerve.

Light-Sensitive Cells in the Retina Rods – responsible for our perception of light and dark, and for peripheral vision. Cones – colour vision receptors Cones are activated by the light they are sensitive to

Angle of Incidence equals Angle of Reflection Reflection: bouncing back of a light ray after hitting a surface. Law of Reflection: when light strikes a smooth, shiny surface, the reflected light ray bounces off the surface at the same angle as it strikes the mirror. Angle of Incidence equals Angle of Reflection

Reflection Normal: an imaginary line at right angles (perpendicular) to the surface. Used as a reference point when measuring angles. Incident Ray: incoming light ray (coming toward the surface) Reflected Ray: outgoing light ray (going away from the surface). Angle of Incidence: i, angle between the incident ray and the normal. Angle of Reflection: r, angle between the refelcted ray and the normal.

Convex and Concave Convex: a surface that is curved outward. Concave: a surface that is curved inward Convex Concave

Reflection – Curved Mirrors Focus or Focal Point: the point at which both reflected rays overlap. Focal Length: the distance from the focal point to the mirror.

Refraction Refraction: the bending of light as it passes through different transparent substances at an angle. Light travels at different speeds through different substances. We call the differences in speed “refraction” – we say light is refracted when it travels from one transparent medium to another.

Refraction For a light ray moving from air to glass: Refracted Ray: the ray that has entered a different medium and bent. Angle of Refraction: the angle between the refracted ray and the normal. For a light ray moving from air to glass: Angle of Refraction is LESS THAN the Angle of Incidence For a light ray moving from glass to air: Angle of Refraction is GREATER THAN the Angle of Incidence

Refraction

Reflection and Refraction Practical Extension We will be talking about lenses in the next few lessons. Using the ray box kits, investigate what happens when parallel light rays are pointed onto a converging lens and diverging lens. Draw a ray diagram for each lens. Describe what you observe happening to the light rays as they pass through the lens. Converging Lens Diverging Lens

Each colour is a different wavelength