What Are the Characteristics of Light Unit E, Chapter 4, pE

Electromagnetic Waves Sunlight travels millions of miles from the sun – Electromagnetic waves: waves of vibrating electric and magnetic fields Radiant energy: energy electromagnetic waves carry Light does not need matter to travel – Vacuum: empty space Speed of light: 300 million m/s All electromagnetic waves travel at the same speed – Have different wavelengths and frequencies » Shorter wavelength = higher frequency » Shorter wavelengths = more energy

Electromagnetic Waves Electromagnetic spectrum – range of wavelengths of electromagnetic waves – Shortest to longest Gamma Rays X-rays Ultraviolet light Visible light Infrared light Microwaves Radio waves

Electromagnetic Waves Visible light – electromagnetic waves that have wavelengths we can see with our eyes – ROY G. BIV Red light has longest wavelengths – cm (650 nm (nanometers)) Violet light has shortest wavelengths Ultraviolet rays – electromagnetic waves that have wavelengths shorter than visible light – Shorter wavelengths mean more energy Honey bees can see these wavelengths Can cause sun burns & skin cancer

Electromagnetic Waves X-rays and gamma rays – Shorter wavelengths and more energy Travel right through your body without being absorbed Medical x-rays are pictures made using x-rays to expose film instead of light Bones absorb x-rays preventing the film being exposed

Electromagnetic Waves Longer wavelengths than visible light – Infrared waves Electromagnetic waves slightly longer than visible light Felt as heat – Microwaves – even longer wavelengths Used in microwave ovens to heat food – Radio waves – longest wavelengths Televisions and radios use different wavelengths – AM (amplitude modulation) & FM (frequency modulation) – VHF (very high frequency) & UHF (ultra-high frequency)

Reflection & Refraction Light is usually not visible as it travels from a light source – You see light waves when they are: Reflected off an object the reflected light enters your eyes – Reflection: the bouncing of light waves off a surface

Reflection & Refraction Objects have different colors because they reflect and absorb different wavelength (colors) of light – White light is a mixture of all colors of light – White object Reflect all colors – Red object Reflect red light // absorb the other colors – Black object Absorbs all colors of light

Reflection & Refraction Different shades of colors – Absorb and reflect different amounts of certain colors Prism separates sunlight into rainbow of colors – Medium: substance light travels through (other than vacuum) – Speed of light changes in different mediums Vacuum: 300 million m/s Slower when traveling through air Even slower when traveling through glass & water

Reflection & Refraction Refraction: the bending of light waves when passing from one medium to another – Prism Refracted when entering prism Refracted when leaving prism – The amount a wave is bent (refracted) depends on the wavelength Shortest wavelengths (Violet) bent the most Longest wavelengths (Red) bent the least

Reflection & Refraction Refraction causes many familiar phenomena – Rainbows Raindrops act like little prisms – Diamonds Multicolored sparkle – Straw sticking out of water Appears bent / broke – Mirage: caused when light travels through air of different temperatures When driving a puddle appears in the distance – Red sunrises/set Sunlight travels through thicker atmosphere Scatters most blue and violet light so much you can’t see it Scatters the red and orange light so you can

Transparent, Opaque, Translucent Transparent: medium, or substances, that light can travel through – Air, water, clear glass, clear plastic Transparent to all wavelengths of light – You can see objects clearly through them – Some objects transparent to only certain colors of light Apple juice is a clear liquid Cherry jello transparent to red light

Transparent, Opaque, Translucent Opaque: substances that light can’t pass through – Absorb or reflect light – Light energy they absorb turns into thermal energy making them warmer Wood, pottery, bricks, animals, and people

Transparent, Opaque, Translucent Translucent: substances that let some light through – You can’t see clearly through them – Light is scattered as it travels through Milky plastics, frosted glass, milky stained glass

Summary Light is electromagnetic waves you can see Light can be reflected, refracted, or absorbed The wavelengths of visible light an object reflects determines its color Refraction is the bending of light – Due to light changing speed when entering a different medium Objects that light can travel through are transparent Objects that absorb and reflect light are opaque Translucent objects transmit some light, but they distort or eliminate images

Homework Read Unit E, Chapter 4, pE Answer ?s on WS or Google Doc