⇒ Electromagnetic radiation often behaves as a wave
⇒ However, other behaviours can only be explained by thinking of electromagnetic radiation as a stream of packets (i.e. quanta) of energy, called photons
⇒ The energy of a proton is proportional to its frequency e.g. the energy of an xray photon is higher than a photon of visible light because the xray photons have a higher frequency
⇒ To calculate the energy of a photon we use the following formula: E = hf
⇒ Since frequency x wavelength = wave speed, we can also write the equation as follows: E = hc⁄wavelength
⇒ The intensity of electromagnetic radiation is the energy transferred per unit time per unit area
⇒ Electromagnetic intensity depends on the energy carried by the photons, the number of photons transferred each second, and the area on which they are incident
⇒ So, the intensity of electromagnetic radiation will increase in the following situations:
⇒ Electrons within an atom can absorb photons and gain energy
⇒ Energy carried by photons and gained by electrons is extremely small, so a different unit of energy is used - the electron volt (eV)
⇒ The work done in electron volts (i.e. the energy transferred) is calculated using the following formula: W = VQ
⇒ To convert electron volts to joules, multiply the energy in electron volts by 1.6 x 10-19 J/eV
⇒ To convert joules to electron volts divide the energy·in joules by 1.6 x 10-19 J/eV
⇒ An electron gains and loses energy as it moves within the atom
⇒ The electron contains both kinetic energy and electrostatic potential energy
⇒ The positive charge of the proton means that the negatively charged electron is attracted to the nucleus, so work must be done to move the electron away from the nucleus (hence why the electron has less energy as it gets closer to the nucleus)
⇒ The electron will move further from the nucleus (i.e. move to a higher energy level) if it gains the right amount of energy by absorbing a photon
⇒ On the other, if the electron loses energy by emitting a photon it will move closer to the nucleus (i.e. move to a lower energy level)
⇒ An electron can only absorb a specific amount of energy (i.e. the possible or allowed energies for electrons are not continuous)
⇒ For example, when you use stairs you can only gain or lose gravitational potential energy in fixed amounts
⇒ Also see our notes on: