Electromagnetic Waves

• Electromagnetic waves form a continuous spectrum.
• An object appears white if all wavelengths are reflected by equal amounts.
• An object appears black if all wavelengths are absorbed.
• The types of electromagnetic radiation can be ordered from lowest to highest frequency as follows: Radio waves, Microwaves, Infrared, Visible Light, Ultraviolet, X-rays, Gamma Rays.
• Electromagnetic waves all travel at the same speed in a vacuum and in air.
• The property of waves in different mediums that causes refraction is velocity, as wave speed is slower in denser materials, causing refraction.
• When waves enter a denser medium, they refract, bending towards the normal and the angle of refraction is less than the angle of incidence.
• Radio waves can be produced by oscillations in an electrical circuit.
• The largest wavelength of visible light is red.
• A red colour filter absorbs all wavelengths of light other than those in the red range of the spectrum, allowing only red light to pass through the filter.
• The highest frequency of visible light is blue.
• Diffuse reflection is the reflection from a rough surface which causes scattering.
• Any wavelengths of light that aren’t reflected by an opaque object are absorbed by the object.
• X-rays and Gamma rays are ionising radiation that can cause mutations in genes and lead to increased risk of developing various cancers.
• The colour of an opaque object is determined by the wavelengths of light that are most strongly reflected, with different objects reflecting different wavelengths of light by different amounts.
• Microwave radiation has practical uses in satellite communications and cooking food.
• A convex lens is represented by a circle in a ray diagram.
• Specular reflection is the reflection from a smooth surface in a single direction.
• Radio waves are used in television transmission and radio transmission.
• Ratios do not require units.
• Gamma rays originate from changes in the nuclei of atoms.
• Concave lenses can only produce virtual images.
• Refraction is the wave phenomenon used by lenses to form an image.
• Parallel rays of light are refracted and brought together at a point known as the principal focus when passing through a convex lens.
• Ultraviolet waves can cause the skin to age prematurely and increase the risk of developing skin cancer.
• Magnification is the ratio between image height and object height.
• Infrared radiation has practical uses in electrical heaters, cooking food, and infrared cameras.
• The focal length of a lens is the distance from the lens to the principal focus.
• Radio waves can induce oscillations in a circuit with the same frequency as the waves themselves.
• Convex lenses can produce real or virtual images.
• The colour of visible light waves is determined by the wavelength and frequency of the light waves.
• A concave lens is represented by a dot in a ray diagram.