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  • Home / Ask Me Stuff
  • Lessons
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      • First Law of Thermodynamics
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      • Introduction to Half-Reactions
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      • Galvanic Cells
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      • Nernst Equation
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      • Introduction
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      • First-Order Reactions
      • Second-Order Reactions
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      • Arrhenius Equation
      • How Long will it Take to Decay?
      • What Order is this Reaction?
      • Find the Rate Constant
      • Find the Activation Energy
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      • Ideal Gas Law
      • Density of Gases
      • Ideal Gas Law and Changes in P, V, T
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      • HCl + Alkene (Adding across a double bond)
      • Reaction of OH with Alkyl Halide
      • What is Regioselectivity?
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      • Average Atomic Mass
      • Solve for Isotopic Abundance
      • Limiting Reagents
      • Percent Yield
      • Actual Yield and Percentage Yield
      • Percent Composition
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      • What's in an Atom?
      • Quantum Numbers
      • Pauli, Aufbau, Hund
      • Light: E h ν λ
      • Energy Levels of Hydrogen
      • Energy Levels of Non-Hydrogen Atoms
    • Organic Naming >
      • Naming Organic Molecules
      • How to Name Amines
      • How to Name Amides
  • Privacy Policy
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Light: Energy, Wavelength, Frequency and Planck's Constant


Light travels in tiny packages called photons.  Each of these photons carries are certain amount of energy, E.  Based on this, we also say that they have a wavelength (λ) and a frequency (ν), and that the three of these are related as follows:
c = λν
E = hν
where c is the speed of light (3.0 x 10^8 m/s) and h is Planck's constant (6.626 x 10^-34 Js).

Wavelength is measured in distance.  It is usually best to convert it to metres.
Frequency is often given in hertz (Hz).  These are the opposite of seconds (s^-1).
Energy is often given in joules.  This is ideal.  If it is given in calories, you must convert is to joules by multiplying by 4.184

Sample Question

Q: What is the wavelength (in nm) of light with a frequency of 4.5 x 10^14 Hz?

A: c = λν, so λ = c/ν.  λ = (3.0 x 10^8 m/s) / (4.5 x 10^14 s^-1) = 6.67 x 10^-7 m = 667 nm.
Created by Nathan Oldridge (aka ChemistNATE).  All lessons here are Public Domain.