Let there be light • Most of what we know about the Universe comes from information that has been carried to us by light. • We will begin by examining the properties of light and then we will discuss the instruments that are used to detect it (telescopes).t.
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Let there be light Most of what we know about the Universe comes from information that has been carried to us by light. We will begin by examining the.
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Transcript
Let there be light• Most of what we
know about the Universe comes from information that has been carried to us by light.
• We will begin by examining the properties of light and then we will discuss the instruments that are used to detect it (telescopes).t.
Light Basics• Light is radiant energy– Radiant energy is energy that can travel through space from one
point to another without the need of a direct physical link
• In empty space light travels at a constant speed, 299,792.458 kilometers per second (this is a constant and is denoted by “c”).
– Fast enough to circle the Earth over 7 times in one second!– When light travels through matter, glass, water, gasses, etc. it
slows down.
• Light can be thought of one of two ways:1. As an electromagnetic wave – a mix of electric and magnetic
energy2. As photons – photons are packets of energy
- Both models have one thing in common – they classify light as being energy
Light As A Wave
Parts of an electromagnetic wave:
• Crest – the high point of a wave
• Trough – the low point of a wave
• Wavelength () – the distance of two wavecrests or two wavetroughs
• Frequency, which is the number of cycles (wavelengths) that pass in a fixed point in a given time.
Looking At Waves Through Sound• We can’t see light waves, but we can look at
sound waves to help us understand wave structure and wave energy.
• Which one of these wave models has the bigger wavelength?
• Which one of these models has the greater frequency?
The Difference Between Light and Sound Waves
• We use sound waves to hear. Even though sound has the same wave structure as light they are fundamentally different.– Sound energy relies on the vibration of sound waves
through matter.
• In other words, sound is transferred from one place to another via direct contact• Light is a form of radiation
–It is not dependant on matter to get form one place to another.
Light is Radiation!!!! Oh No!!!!
• Yes, light is radiation. It is one of many types of radiation. All this means is that it can travel through space without the need for a direct transfer of energy.– Sound was the opposite. It moves because of a direct transfer
• We can use what we already know and some simple concepts to help us out.– We know that every form of radiation
behaves as a wave– We also know that each type of radiation
moves at a constant speed through empty space (“c”)
– Furthermore, we know that some waves have a higher frequency than others
– Lastly we know that different radiations different wavelengths
Looking at it another way…
Wavelength (λ) x Frequency (f) = The Speed of Light (c)
Or
λ x f = cWhen we look at this we can notice a couple of
things
1. The speed of light (c) is a constant (3.0 x 108 meters/sec)
2. High frequency = short wavelength
3. Low frequency = large wavelength
4. Wavelength and frequency are inversely proportional
Wait, what about energy? How is energy related to λ = c/f ?• To help us with this lets take a small trip to this place and learn about a guy named Max Planck.
• Now we have Planck’s constant (h)
• Planck said that Energy (E) = h (constant) x frequency (f)
• If we take λ x f = c and solve for frequency(f), than we get