GW 3.1 Electromagnetic Radiation

What are the four types of energy trnasfer?

1. Convection

2. Latent heat

3. Conduction

4. Radiation

Convection

• When a fluid (liquid or gas) moves to carry heat from one place to another

• Ex: You are standing in a shallow region of a pond, and the water suddenly briefly feels hotter or colder

Latent heat

• When you evaporate water (which takes energy), then the water vapor moves and condenses somewhere else, which releases energy

• Ex: Your hand gets really hot (and also wet!) when you put it over a pot of boiling water

Conduction

• When heat is moved through a material by its molecules jiggling together

• We can’t see any motion occurring on a human scale

Electromagnetic radiation

• the sun creates a lot of energy and some of it reaches Earth by waves of light

• propagates oscillations (or waves) in electric and magnetic fields

• everything emits electromagnetic radiation al the time

  • the amount emitted depends on its temperature and properties

  • hotter things = emit more electromagnetic radiation at shorter wavelengths

  • cooler things = emit less electromagnetic radiation at longer wavelengths

• frequency (v)

• wavelength (λ)

What is frequency (v) ?

• the number of times wave crests pass you per second

• the speed of wave is equal to the product of its frequency and wavelength

  • c = λv

What is the speed of light in a vacuum?

c - 3.0 × 10^8 m s^-1

Does the speed of light depend on the wavelength of light? Why or why not?

• No

• b/c light travels through the atmosphere only very slightly slower than it travels through a vacuum

• we can approximate the speed of light in the atmosphere as the speed of light in a vacuum

Electromagnetic spectrum (shortest to longest wavelength)

• Gamma rays

• X-rays

• Ultra-violet

• Infrared

• Microwaves

• Radio

On the electromagnetic spectrum, what is the relationship between wavelength and energy?

• The shorter the wavelength, the higher the energy

• The longer the wavelength, the lower the energy

In addition to a wave, electromagnetic radiation is considered a what?

• A photon

  • The energy of a photon is proportional to its frequency

  • Light with shorter wavelengths is associated with higher energy photons