YouTube Transcript:
Chapter 3.1c Photoelectric Effect

Skip watching entire videos - get the full transcript, search for keywords, and copy with one click.

Video Transcript

View:

the topic of this video is

electromagnetic energy and specifically

the photoelectric effect

uh we'll be describing the particle

nature of light in this video

before i jump into um some observations

of the photoelectric effect i just want to

uh briefly describe what the

photoelectric effect is based off of so

there's an observation that if we take

a metal plate okay so this is a metal plate

plate

if you shine light onto it

okay uh what sometimes depending on the

light source

we can actually observe so this is light

coming in

we can observe an electron or electrons

being ejected from

the surface of the metal plate and the

energy of those electrons

can be uh determined based off of the

velocity that they are ejected from the plate

plate

so what is the photoelectric effect then

let's take a look uh we have three

examples of different wavelengths here

so we have 700 nanometer

light 700 nanometer 550 nanometer and

400 nanometer

so the the uh

what i want to do before jumping into

the observation is to to remind you that

at 700 nanometer

light this is going to be the um

low frequency light in this particular

case 550 nanometer light is going to be the

the

medium frequency and 400 nanometer is

going to be the

high frequency so remember frequency and

wavelength are inversely related so the

higher the wavelength the lower the

frequency and vice versa

so in the case of 700 nanometer light on

the left what happens is

um when this light is being uh

exposed to the metal surface no

electrons are ejected

even if you increase the the brightness

of the light source

okay you increase the brightness of the

light source no electrons are ejected

which is an interesting

thing because if light is behaving

exactly as

a wave and only as a wave then

increasing the brightness should

in theory increase the energy of the

wave okay that's sort of the classical

view of

of waves but what we can see here is that

that

so so this uh no electrons are ejected

at 700 nanometers regardless of the

intensity of the light

but for 550 nanometer light which is has

a higher frequency

we do see electrons being ejected at a

velocity of 2.96 times 10 to the fifth

meters per second

if we increase the frequency yet again or

decrease the wavelength however you want

to view it

what we see is not only are electrons

still being ejected

right but they are being ejected now

with even greater kinetic energy at

with a with a velocity of six point two

two times ten to the fifth

meters per second so so really what this

exposed was a was a a paradox that

if light strictly behaved as a wave

there's no way that that could this these

these

um observations could could uh uh be

explained with a wave

alone because again increasing the

intensity of 700 nanometer light

did not cause electrons to be ejected

from the surface

it appears that there is some energy

quantization happening in the light itself

itself

that is not dependent on the amplitude

of the light but on the frequency

or the wavelength however you want to

view it and recall that this is what max

planck had been working on

quantized energy of emission from black

body radiators

so einstein made the connection there

before i jump into um

the uh the equation well i guess it's up

here i'll give i'll write out the

equation again in one second but

in general what i want you to also keep

in mind is that

when energy is released

by us by a substance or a system when

energy is released by system we call this

exothermic

and when energy is absorbed

by a system we call this endothermic

okay um so the equation then

that um einstein used to assign

to enable us to calculate energy of of light

light

particles is energy is equal to planck's

constant times

frequency um so he's just pretty much

applying planck's

quantization here to now think about

uh light as particles

as well as waves okay so if we think

about um

light as

particles this is what we refer to as

photons okay so when we think about a

photon we are thinking about a discrete

particle of electromagnetic energy

and again this is now referring to

something called the wave particle

duality if we take

electromagnetic radiation and do an

experiment like the double slit

experiment we see into an interference pattern

pattern

which is the culmination of constructive

and interference

of waves so that's clearly as a wave feature

feature

but if we do with the photoelectric

effect we see behaviors that can only be

explained by particles

okay so so this is considered the wave

particle duality so let's go ahead and

use this equation

now which we can now think about um

uh is really useful for energy being

absorbed or emitted by

uh substances to solve a practice problem

problem

so you can pause the video now if you

want to write this down in your notes

i'm going to go ahead and jump into it

so we have light from a neon sign

we are observing radiation from excited

neon atoms okay so the neon atoms are

emitting energy this is an exothermic

process you could say

and if this radiation has a wavelength

of 640

nanometers what is the energy of the

photon being emitted well we have this

equation the energy of light being

emitted is equal to

planck's constant times the speed of

light over wavelength so let's go ahead

and plug those

in 6.626 times 10 to the negative 34

joules seconds that's multiplied by each

other those units

that's a constant multiplied by another

constant 2.998 times 10 to the 8

meters per second i'm using the s to the

negative 1 to indicate per second

and we're going to divide all of that by

640 nanometers but right away you should

be looking for units to be cancelling out

out

and what we can see here is that

reciprocal seconds will cancel out with

seconds on the top

but meters on the top cannot cancel out

with nanometers we have to reconcile

those units so we're going to convert nanometers

nanometers

to meters in the bottom so i'm putting

nanometers down here

and meters on top nanometers will cancel

here and meters will cancel

between the entire denominator and the

entire numerator

now we need the actual unit conversion here

here

so we know that in one nanometer that is

equal to a really small value of meters

one times ten to the negative ninth

meters so now all we're left with in

terms of units

is uh joules which isn't the unit of

is a unit of energy so

we have three this should give you 3.10

times 10 to the negative

Click on any text or timestamp to jump to that moment in the video

Most transcripts ready in under 5 seconds

One-Click Copy125+ LanguagesSearch ContentJump to Timestamps

Paste YouTube URL

Enter any YouTube video link to get the full transcript

Most transcripts ready in under 5 seconds

Get Our Chrome Extension

Get transcripts instantly without leaving YouTube. Install our Chrome extension for one-click access to any video's transcript directly on the watch page.

Add to Chrome — Free

Works with YouTube, Coursera, Udemy and more educational platforms

Get Instant Transcripts: Just Edit the Domain in Your Address Bar!

YouTube

←

→

↻

https://www.youtube.com/watch?v=UF8uR6Z6KLc

YoutubeToText

←

→

↻

https://youtubetotext.net/watch?v=UF8uR6Z6KLc

YouTube Transcript:Chapter 3.1c Photoelectric Effect

Video Transcript

Paste YouTube URL

Transcript Extraction Form

Get Our Chrome Extension

Get Instant Transcripts: Just Edit the Domain in Your Address Bar!

YouTube Transcript:
Chapter 3.1c Photoelectric Effect