⇒ Energy is measured in joules
⇒ Charge (Q) is measured in coulombs (C)
⇒ In an atom, the central nucleus is positively charged and the surrounding electrons are negatively charged
⇒ A neutral atom has the same number of protons and electrons. It becomes ionised when it gains or loses electrons
⇒ There is a spectrum of electromagnetic radiation
⇒ In order of decreasing wavelength (i.e from long to short) the electromagnetic spectrum is as follows: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays
⇒ Electromagnetic radiation carries information across the universe at the speed of light
⇒ Every chemical element has a unique 'signature' (i.e. emission spectrum) which can be revealed by analysing the light it gives off by spreading the light out into a spectrum
⇒ Light from distant galaxies takes billions of Earth to reach us, by which time the spectrum from the galaxies has red shifted (i.e. the wavelength of the light has been lenghtened), meaning we can tell the speed and distance of each galaxy from Earth (and, therefore, the age of the universe)
⇒ Line spectra can be used for many different things e.g. identifying samples of illegal drugs
⇒ Also see our notes on: