so let's take a break from atoms look at something else

light. for some time we had known light to behave as an

electromagnetic wave, for this reason light is also called electromagnetic

radiation

light waves have both a wavelength, the distance from tip to tip

and a frequency, the number of waves that pass by a point per unit time

they are inversely proportional since the shorter the wave

the more of them that can go by per second resulting in a higher frequency

these variables are related by the following equation:

in which c is the speed of light, about 300 million meters per second

the speed limit of the universe. the electromagnetic spectrum

shows light of all the different wavelengths from gamma rays to radio

waves

including this tiny sliver in the middle which is visible light

the light we can detect with our eyeballs. the wave theory of light

was very useful for a time but it could not explain

the photoelectric effect. this was the observation

that if a certain metal plate is irradiated with light an electron is

ejected

which can be detected when it interacts with a positively charged wire or

plate sensor.

the incongruity was that the ability of the light to eject an electron

depends only on its frequency and not its intensity

so if the beam was below a certain frequency even a very intense beam

with a lot of light could not eject an electron whereas

above a certain frequency the faintest beam possible

could do it. this seem strange and a famous fellow named

albert Einstein solved the problem by extending a concept developed by max

planck

just five years prior. planck proposed that energy is not continuous

but rather is quantized, that is all energies

are multiples of the smallest fundamental unit of energy

the plank energy. in fact quantum theory went on to show that everything is

quantized

space and time too, so you can't infinitely subdivide them

you'll eventually get to a smallest thing that can't be divided further

but more on that in the physics course.

einstein extended what planck said about energy

and rationalized that light must also be made of quanta

which he called photons. these are particles of light

this explains the photoelectric effect because an electron is ejected

when struck by a singular photon with sufficient energy

it only takes one photon so even the faintest beam

above a certain frequency will be able to do it but if none of them are of that

minimum energy

no matter how many photons strike the sample an electron will not be ejected

it was found that the energy of the photon can be given by the following

equation:

according to the frequency of the photon and planck's constant

we now have to accept that light obeys

wave-particle duality, meaning it is both a particle

and a wave at the same time. confused? you should be

this is the first discovery in a series that brought about the quantum

revolution

completely changing the landscape of physics and how we view the universe

Newton's Laws no longer reign supreme

in the world of the very small and the universe became much stranger

almost overnight thanks to Einstein and others

that were inspired by him. thanks for watching guys, subscribe to my channel

for more tutorials

and as always feel free to email me