Energy. Radiant Energy Radiant: think light…. How does light carry energy through space???
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Transcript of Energy. Radiant Energy Radiant: think light…. How does light carry energy through space???
Radiant EnergyRadiant Energy
• Radiant: think light….
• How does light carry energy through space???
WavesWaves• Light waves
– electromagnetic – consist of an electric & magnetic fields
oscillating at right angles to each other in direction of motion
WAVE WAVE CHARACTERISTICSCHARACTERISTICS• WavelengthWavelength –
distance between crests
• AmplitudeAmplitude – height of wave from origin to crest or peak– Brightness
• FrequencyFrequency – how fast a wave oscillates – The number of
times a wave completes an up and down cycle
– Measured in cycles per second
– s-1 = 1/s = hertz = Hz
Speed of LightSpeed of Light
• constant speed in space
c = 3.00 x 108 m/s
For all waves,• The shorter the wavelength () of a
wave, higher the frequency ()• c = x = c/
Practice ProblemPractice Problem
• Calculate the wavelength of a radio wave with a frequency of 93.1 x 106 s-1
= c/ = 3.00 x 108 m/s / 93.1 x 106 s-1
= 3.22 m
• Beyond red is the infrared portion. This is also called radiant heat– Used in microwaves,
radio waves, tv waves
Electromagnetic SpectrumElectromagnetic Spectrum
• Beyond violet is the ultraviolet radiation (UV)– Responsible for
sunburns and skin cancer.
– X-rays are even shorter in wavelength
Electromagnetic SpectrumElectromagnetic Spectrum
Planck’s TheoryPlanck’s Theory
• Max Planck predicted accurately how the spectrum of radiation emitted by an object changes with temperature
• Proposed that there is a fundamental restriction on amounts of energy that an object emits or absorbs, called quantum.– Means FIXED AMOUNTS
• Related the Frequency of the radiation to the amount of energy.
• E = h
• Energy = Planck’s Constant x Frequency
Know Planck’s Constant Know Planck’s Constant
(h) = 6.6262 x 10(h) = 6.6262 x 10-34-34 J-s (Joule x second) J-s (Joule x second)
• Energies absorbed or emitted by atoms are quantized, which means that their values are restricted to certain quantities.
• Energy is not continuous!
• Quantized Continuous
Planck’s Theory AppliedPlanck’s Theory Applied
• Determining temperatures of distant planets and stars by measuring the wavelengths of the EM radiation that they emit
• Why can’t we see quantized energy– Planck’s Constant is very small.– Quanta are too small for every day notice,
but to a very small atom they make a big difference!
The Photoelectric EffectThe Photoelectric Effect(Einstein thanks Planck…)(Einstein thanks Planck…)
• electrons ejected from surface of a metal when light shines on it
• Einstein realized that Planck’s idea of energy quanta could explain this
• Light consists of quanta of energy that behave like tiny particles, called PHOTONS– Each photon carries an amount of energy
given by Planck’s equation.