Photoelectric Effect Theory Lesson

Summary

This educational script delves into the photoelectric effect, emphasizing the particle nature of light. It outlines the electromagnetic spectrum, detailing the relationship between frequency, wavelength, and energy of photons. The script explains how photons with higher frequency possess more energy, behaving more like particles, particularly with gamma rays. It introduces Planck's constant and the equations governing the photoelectric effect, including the work function and kinetic energy of emitted electrons. The threshold frequency for electron ejection and the impact of light intensity on photocells are also discussed, providing a comprehensive overview of the fundamental principles of quantum physics.

Takeaways

• 🌌 The electromagnetic spectrum consists of seven parts, ranging from gamma rays to radio waves, with gamma rays having the highest frequency and radio waves the lowest.
• 🔄 All electromagnetic waves are transverse waves that travel at the speed of light (3 x 10^8 m/s) in a vacuum and carry energy in the form of photons.
• ⚡ The energy of photons is directly proportional to the frequency of the electromagnetic waves, with gamma rays having the highest energy due to their high frequency.
• 📉 Photons with higher frequencies exhibit more particle-like behavior, while those with lower frequencies show more wave-like properties.
• 🔬 The photoelectric effect demonstrates the particle nature of light, where electrons are ejected from a metal surface when struck by light of a suitable frequency.
• ⚡️ Each metal has a specific threshold frequency, which is the minimum frequency required for the photoelectric effect to occur, and is directly related to the work function of the metal.
• 📉 The kinetic energy of emitted electrons (photoelectrons) is directly related to the frequency of the incident light, following the equation EK = hf - W0, where EK is the kinetic energy, hf is the energy of the photon, and W0 is the work function.
• 📊 The graph of kinetic energy versus frequency for emitted electrons is a straight line with a slope equal to Planck's constant, and the y-intercept representing the work function of the metal.
• 🔑 The work function and threshold frequency of a metal are indicators of how tightly electrons are bound to the metal's atoms, with higher values meaning electrons are more tightly bound.
• 🔆 The intensity of incident light affects the number of photoelectrons emitted, leading to a stronger current in a photocell, while the frequency of the light affects the kinetic energy of the emitted electrons.

Q & A

What are the seven parts of the electromagnetic spectrum?

The electromagnetic spectrum consists of gamma rays, x-rays, ultraviolet, visible light, infrared, microwaves, and radio waves.

What is the relationship between wavelength and frequency in electromagnetic waves?

The frequency of electromagnetic waves is inversely proportional to their wavelength. The shorter the wavelength, the higher the frequency, and vice versa.

How does the energy of photons relate to the frequency of electromagnetic waves?

The energy of photons is directly proportional to the frequency of the electromagnetic waves. Higher frequency waves carry photons with greater energy.

What is the significance of Planck's constant in the context of photon energy?

Planck's constant (6.63 x 10^-34 joules seconds) is used in the equation E = h * f to calculate the energy of a photon, where E is the energy, h is Planck's constant, and f is the frequency of the electromagnetic wave.

What is the photoelectric effect and its significance in understanding the particle nature of light?

The photoelectric effect is the emission of electrons from a metal surface when light of a suitable frequency shines on it. It demonstrates the particle nature of light, as electrons are ejected due to the energy of individual photons.

What is the threshold frequency, and how does it relate to the photoelectric effect?

The threshold frequency is the minimum frequency of light required to eject electrons from a metal surface. If the frequency of the incident light is higher than this threshold, electrons will be emitted.

How is the work function of a metal related to its threshold frequency?

The work function of a metal is the minimum energy needed for an electron to be emitted from the metal surface. It is calculated using the equation W0 = h * f0, where W0 is the work function, h is Planck's constant, and f0 is the threshold frequency.

What is the kinetic energy of photoelectrons in relation to the frequency of incident light?

The kinetic energy of photoelectrons (EK) is given by the equation EK = hf - W0, where hf is the energy of the incident photon and W0 is the work function of the metal. The higher the frequency of the incident light, the greater the kinetic energy of the emitted electrons, provided the frequency is above the threshold frequency.

How does the intensity of incident light affect the photoelectric effect?

An increase in the intensity of incident light increases the number of photons striking the metal, which in turn increases the number of electrons emitted and the current strength in a photocell, but it does not affect the kinetic energy of the individual photoelectrons.

What can be inferred about the binding energy of electrons in metals from their threshold frequencies?

Metals with higher threshold frequencies require more energy to eject electrons, indicating that electrons are more tightly bound to the metal's atoms. Conversely, metals with lower threshold frequencies have electrons that are more loosely bound and can be ejected with less energy.

Outlines

00:00

🌈 Understanding the Electromagnetic Spectrum and Light Energy

The paragraph explains the electromagnetic spectrum, highlighting the different types of waves from gamma rays to radio waves. It describes the relationships between frequency, wavelength, and energy, explaining how shorter wavelengths correspond to higher frequencies and energy. It introduces photons as energy carriers, showing how the energy of photons is proportional to frequency. Planck’s constant is introduced as part of an equation to calculate photon energy, with gamma rays behaving most like particles due to their high frequency and energy.

05:02

🌟 The Dual Nature of Light

This paragraph discusses the concept of the dual nature of light, noting that visible light exhibits both wave-like and particle-like properties. It also touches on the relationship between frequency and wavelength, emphasizing that higher frequency leads to shorter wavelengths. The wave equation is used to show that frequency and wavelength are inversely proportional. Wave behaviors such as refraction, diffraction, and interference are reviewed as evidence of light's wave nature, while the photoelectric effect serves as proof of light's particle nature.

10:04

⚡ The Photoelectric Effect and its Key Equations

The focus shifts to the photoelectric effect, describing how electrons are ejected from a metal surface when light above a certain frequency strikes it. The threshold frequency is introduced as the minimum frequency needed to eject electrons, along with the concept of the work function, which is the minimum energy required for an electron to leave the surface. Key equations are provided for calculating photon energy, work function, and kinetic energy, stressing the importance of knowing these values when analyzing the photoelectric effect.

15:07

📊 Kinetic Energy and Frequency Graphs in the Photoelectric Effect

This section details how to interpret graphs related to the photoelectric effect, specifically the kinetic energy versus frequency graph. The equation E_k = h(f - f_0) is manipulated to fit the linear graph model. Planck’s constant is identified as the gradient of the graph, while the work function appears as the y-intercept. The x-intercept corresponds to the threshold frequency. The paragraph also compares different metals based on their threshold frequencies and work functions, showing how higher frequencies result in greater kinetic energy for ejected electrons.

20:09

🔬 Electroscope and the Role of Photon Energy

The behavior of electroscopes under different light conditions is explored. When red laser light or ultraviolet light is shone onto a positively or negatively charged electroscope, the effects vary based on the energy of the light. Red light, with low energy, has no effect, while ultraviolet light, with higher energy, can cause electrons to be emitted from the negatively charged electroscope, leading to a loss of charge. The explanation emphasizes how the energy of photons, determined by the frequency of light, impacts electron behavior.

💡 Photoelectric Cells and Light Intensity

This paragraph covers the function of a photoelectric cell, where incident light causes electrons to move from the cathode to the anode, generating a current. The frequency of the light must exceed the threshold frequency to emit electrons, and increasing the frequency boosts the kinetic energy of the electrons. The intensity of the light, linked to the number of photons, increases the number of electrons emitted and, consequently, the current measured. A distinction is made between the effects of frequency and intensity on electron emission and current generation.

Keywords

💡Electromagnetic Spectrum

The electromagnetic spectrum refers to the range of all types of electromagnetic radiation. This includes gamma rays, x-rays, ultraviolet light, visible light, infrared, microwaves, and radio waves. In the video, it's essential because understanding the behavior of light, including the photoelectric effect, requires knowledge of where different forms of light, like gamma rays or microwaves, fit in the spectrum.

💡Photon

A photon is a particle representing a quantum of light or other electromagnetic radiation. It carries energy proportional to the radiation frequency. In the video, photons are central to understanding the photoelectric effect, as they are the particles that strike a metal surface, potentially causing electrons to be emitted based on their energy.

💡Frequency

Frequency refers to the number of wave cycles that pass a given point per second, measured in Hertz (Hz). Higher frequency waves, like gamma rays, have more energy, while lower frequency waves, like radio waves, have less. In the video, frequency is crucial in determining both the energy of photons and their behavior in phenomena like the photoelectric effect.

💡Wavelength

Wavelength is the distance between successive crests of a wave, typically measured in meters. It's inversely proportional to frequency, meaning shorter wavelengths correspond to higher frequencies. In the context of the video, wavelength helps explain the relationship between energy and frequency of electromagnetic waves, affecting whether electrons are emitted in the photoelectric effect.

💡Photoelectric Effect

The photoelectric effect is the emission of electrons from a material, typically a metal, when it is exposed to light of sufficient frequency. The video explains how photons of light, if above a certain threshold frequency, can cause electrons to be emitted from a metal surface, a phenomenon crucial for demonstrating the particle nature of light.

💡Planck's Constant

Planck's constant is a fundamental constant, represented by 'h', used to describe the quantization of energy. Its value is 6.63 × 10^-34 joule-seconds. In the video, it is used in the formula E = hf to calculate the energy of photons, showing that energy is directly proportional to the frequency of light.

💡Threshold Frequency

Threshold frequency is the minimum frequency of light required to eject an electron from a metal surface. In the video, this concept is key to understanding why not all light can cause the photoelectric effect—only light with a frequency above this threshold can cause electron emission.

💡Work Function

The work function is the minimum amount of energy needed to remove an electron from the surface of a metal. The video discusses how the energy of incident photons must exceed this work function for electrons to be emitted, linking this concept to the threshold frequency in the context of the photoelectric effect.

💡Kinetic Energy of Emitted Electrons

The kinetic energy of emitted electrons is the energy that an electron has after being ejected from a metal surface, dependent on the excess energy from the photon after overcoming the work function. In the video, this is explained using the equation EK = hf - W0, where any excess energy after the work function is converted into the electron's kinetic energy.

💡Wave-Particle Duality

Wave-particle duality refers to the concept that light and other forms of electromagnetic radiation exhibit both wave-like and particle-like properties. In the video, this duality is explored through the photoelectric effect, where light behaves like a particle (photon) to eject electrons, but also has wave characteristics, like wavelength and frequency.

Highlights

The electromagnetic spectrum is composed of seven parts, ranging from gamma rays to radio waves.

Gamma rays have the highest frequency and shortest wavelength, while radio waves have the lowest frequency and longest wavelength.

The speed of all electromagnetic waves is a constant 3 x 10^8 meters per second.

Electromagnetic waves carry energy in discrete packets called photons, whose energy is dependent on frequency.

The energy of photons is calculated using the equation E = hν, where h is Planck's constant and ν is the frequency.

Photons with higher frequency have greater energy and exhibit more particle-like behavior.

The photoelectric effect demonstrates the particle nature of light, where electrons are ejected from a metal surface upon exposure to light of suitable frequency.

Each metal has a threshold frequency, which is the minimum frequency required to emit electrons.

The work function of a metal is the minimum energy needed for an electron to be emitted from its surface.

Electrons emitted from a metal due to the influence of photons are called photoelectrons.

The kinetic energy of emitted electrons can be calculated using the equation EK = hf - W0, where W0 is the work function.

The graph of kinetic energy versus frequency for emitted electrons is a straight line with a slope equal to Planck's constant.

Different metals have different threshold frequencies and work functions, affecting how tightly electrons are bound.

An electroscope can be used to demonstrate the effects of different frequencies of light on the emission of electrons.

A photo cell operates by emitting electrons when photons fall onto the cathode, generating an electric current.

The intensity of incident light affects the current strength in a photo cell, while the frequency affects the kinetic energy of the emitted electrons.

Transcripts

the photoelectric effect and the

particle nature of light before we can

study the photoelectric effect we need

to look at the electromagnetic spectrum

there's some facts that you really need

to know very well the electromagnetic

spectrum is made up of seven parts from

gamma rays right down to radio waves so

the highest frequency electromagnetic

waves are the gamma rays they go from

gamma rays to x-rays in ultraviolet then

a small section is our visible light

infrared microwaves and radio waves

radio waves have the longest wavelength

gamma waves have the shortest wavelength

the shorter the wavelength the higher

the frequency the longer the wavelength

the lower the frequency all of these

waves are transverse waves they all

travel at 3 times 10 to the 8 meters per

second this value is given to you on

your data sheet they can all travel

through a vacuum they don't need any

mechanical particles to move and they

all obey the wave equation where we can

say V for speed is frequency times

wavelengths but when we speak about

electromagnetic waves we can use a C in

the place of the V we see is 3 times 10

to the 8th meters per second as

mentioned over there electromagnetic

waves carry energy in packages and we

call these packages of photons think of

photo which has to do with light the

energy of the photons is dependent on

the frequency of the electromagnetic

waves and as you can remember from the

previous sketch that we had gamma rays

had the highest frequency so the photons

would have the highest energy it's all

according to this equation this is the

energy of your photons of your

electromagnetic waves so the higher the

frequency the higher the energy H is

Planck's constant 6.6 3 times 10 to the

negative 34 joules times seconds

remember it's not joules per second or

you can give the equation as Planck's

constant times the speed of

electromagnetic waves

by the wavelength because frequency is

equal to speed divided by wavelength the

higher the frequency of the photons the

greater the energy of the photons the

more the photons will behave like

particles if they have high frequency so

obviously then gamma rays which have the

highest frequency of all electromagnetic

waves will have the highest energy and

they will behave the most like particles

if we take this equation and we make our

constant a 1 the equal sign becomes a

proportionality so energy of your

photons is directly proportional to the

frequency of the photons they can ask

you to draw the graph for this it is

normally not in your textbooks or it

will be one of the options for a

multiple choice question so frequency of

your photons determines the energy of

the photons it's a direct

proportionality therefore it is a

straight line graph through the origin

so I've used x-rays as an example there

the second highest section of on our

range of electromagnetic waves after

gamma rays x-rays with a very high

frequency have more particle nature than

wave nature because they have high

energy the higher the energy of the

photons the more they're behave like

particles we are now going to look at

the relationship between the energy of

the photons and the wavelength of the

electromagnetic waves if you remember

again gamma rays are on the left-hand

side of the sketch so they have the

shortest wavelength the shorter the

wavelength the greater the energy of the

photons it comes from this equation H is

Planck's constant C is the speed of all

electromagnetic waves these two values

are constants make them a 1 and your

equal sign becomes a proportionality so

energy of your photons is inversely

proportional to the wavelength do not

say in directly use the word inversely

if we plot a graph of the energy versus

the wavelength will have an inverse

proportionality graph but if we plot the

graph of energy of the photons versus 1

over wavelength that is a direct

proportionality so that will give us a

straight line graph to

back to the particle nature and the wave

nature of the spectrum the lower the

frequency of the photons the lower the

energy of the photons they will behave

more like waves so for example

microwaves which are second from the

right-hand side on the sketch that we

have they are the second shortest of all

our electromagnetic waves they have low

frequency therefore long wavelengths

they will have more wave nature than

particle nature the invisible light it

falls in the middle of the

electromagnetic spectrum it therefore

has dual nature it has wave nature and

particle nature you might hear someone

talk about the dual nature of light that

is because light visible light has wave

nature and particle nature when more

growth that I would like to look at is

the graph of frequency versus wavelength

remember from our wave equation the

speed of electromagnetic waves is equal

to the product of the frequency and the

wavelength of the waves the higher the

frequency the lower the wavelength will

the lower the frequency the longer the

wavelength because these two values

always have to multiply to give you the

same constant three times ten to the

eighth meters per second so frequency is

therefore inversely proportional to

wavelength and our graph would give the

inverse proportionality if they asked

you to draw a graph of frequency versus

one over wavelength it would be a

straight line graph

through the origin the higher the

frequency the shorter the wavelength

because frequency and wavelength or

inverse proportionality x' in grade 11

you did two chapters on wave nature you

did a chapter on the refraction of light

using Snell's law and you also did a

chapter on 2d and 3d waves which

involved diffraction and interference so

diffraction interference and refraction

are all proof of wave nature proof of

particle nature is the photoelectric

effect and that is what we are doing in

grade 12 so you must know that

Nishan of the photoelectric effect it is

the process whereby electrons are

ejected from a metal surface when light

of suitable frequency is incident on

that surface in order to eject electrons

from a metal the frequency of the

incident light must be greater than the

threshold frequency of the metal each

metal has its own particular threshold

frequency so if your frequency of your

incident light of the from the

electromagnetic spectrum is greater than

the threshold frequency of the metal

electrons will be emitted or ejected

from that piece of metal another word

for threshold frequency is called the

cut-off frequency the definition of

threshold frequency or cutoff frequency

it is the minimum frequency of light

needed to emit electrons from a certain

metal surface the symbol that we use is

a small letter F with a subscript 0

please make your subscripts look like

subscripts a lot of you are being

penalized in your tests and exams

because your subscripts are written too

high or too big the definition for the

work function which is the capital W for

work with a subscript zero work function

is the minimum energy that an electron

in the metal needs to be emitted from

the metal surface so to calculate work

function it is Planck's constant times

the threshold frequency for that

particular metal threshold frequency and

work function offset or they are fixed

for each particular metal that does not

change if the energy of the photons is

greater than the work function of the

metal electrons will be emitted with a

certain kinetic energy EK the following

equations are all extremely important

but they are given to you on your data

sheets this is the energy of the photon

that is incident on the metal so there

is your electromagnetic photon incident

metal this rectangular thing here is our

metal and these are our electrons inside

the metal the work function w0 is the

amount of energy needed to get the

electron from within the middle to the

surface and then if there is any energy

remaining that will be the kinetic

energy with which the electron moves

away from our metal surface E is

calculated by Planck's constant times

the frequency of your incident light

there it is

w0 is your work function which is

calculated by Planck's constant times

the threshold frequency of the middle

and EK is the normal equation for

calculating kinetic energy half MV

squared the mass of an electron is given

to you on your daughter sheet please

remember that you might get a question

in the exam and they don't give you the

mass of an electron you do actually have

it it's on the data sheet a quick look

at the sketch again this is the photon

of light from your electromagnetic

spectrum falling in on your metal he is

equal to H if in red there we go the

work function in green is the energy

needed to get the electron to the

surface and then the energy in blue is

the kinetic energy of the electron as it

moves away from the metal surface if

your energy of your photon is equal to

the work function your electron will

just be able to go to the surface it

will have no extra kinetic energy to

move away from the surface of the metal

the electrons that are removed from a

metal and the influence of photons are

called photo electrons there are normal

electrons but they're called photo

electrons we are now going to study the

kinetic energy versus frequency graph

for the emitted electrons for now just

ignore the graph and look on the

right-hand side if we consider the

general equation for straight line graph

you know it is y equals MX plus

C or F of X equals MX plus C this is

your vertical axis so in this case it's

kinetic energy M is your gradient X is

your horizontal axis in this case it is

the frequency of the incident light and

C is your y-intercept we are going to

arrange our equation which was e equals

W zero plus e K but in the place of E

I'm putting in H F and we are going to

manipulate this equation to fit the axes

of the graph so I want EK to be on the

left hand side where the Y is because

it's my vertical axis and I want

frequency to be in the place where X is

because that is my horizontal axis so

the equation becomes this EK equals hf

minus the work function so I made EK the

subject of the equation if you - work

function on both sides it becomes H if -

work function so that is what our

equation looks like now it is the same

form as the general equation for

straight line graph y equals MX plus C Y

is our e K our vertical axis H is M

which is the gradient so you can see the

gradient of this graph is Planck's

constant the slope represents H Planck's

constant X in this case is our frequency

and C is our work function so the

y-intercept of this graph is the work

function you can see this is an energy

energy and work are in joules this is

our energy axis and that is our

frequency axis the x intercept or the

frequency intercept is the threshold

frequency of our particular metal and

once again the slope is the the gradient

is Planck's constant so this is the

graph for EK equals h if - work function

there at the equation is w 0 work

function of the metal is the intercept

of the vertical axis and the gradient

represents Planck's constant all of

these graphs will have the same gradient

irrespective of which metal we use and

irrespective of which section we use

from the electromagnetic spectrum as you

can see from this graph any frequency

lower than the threshold frequency will

not give the electron any kinetic energy

to leave the metal the frequency that is

equal to the threshold frequency will

not give the electron any kinetic energy

but it will just get the electron to the

surface of the metal if I choose a

frequency slightly higher than the

threshold frequency say for example a

frequency over here you would take that

frequency

draw your dotted line up to your graph

draw it across and then you could read

off what the kinetic energy of that

electron would be as it leaves the metal

the higher the frequency of the incident

light as long as it's above the

threshold frequency higher frequency

will give your electron a higher kinetic

energy as it leaves the metal in this

sketch we have a few graphs for

different types of metals the same as

the previous graph on the vertical axis

we have the maximum kinetic energy of

the electron which is leaving the metal

on the horizontal axis we have the

frequency of the incident light the

threshold frequency is given for each

particular metal as you can see each

particular metal has its own threshold

frequency so we'll look at potassium

potassium first this is the threshold

frequency potassium has the lowest

threshold frequency there is its work

function for sodium the work function

will be lower down it will be weird

intercepts with a vertical axis and it's

threshold frequency is higher it has

greater work function and greater

threshold frequency if we go up to

platinum of all these metals

in them has the highest highest

threshold frequency so it needs the most

energy to get an electron to the surface

I want you also to notice that all of

these graphs have the same slope they

have the same gradient because the

gradient represents Planck's constant it

will never change you will always have

the same gradient you have the value for

Planck's constant 6.6 3 times 10 to the

negative 34 joules times second so if

you were ever asked to calculate

anything from a graph like this and you

have certain values that you can read

off remember you have the gradient of

the graph the question above the graph

is which metal requires the greatest or

minimum energy to begin to eject

electrons which metal requires the least

energy to eject electrons potassium

requires the least energy it's got the

lowest threshold frequency and the

lowest work function

potassium requires the most energy to

release electrons because it has the

highest threshold frequency and it would

have the highest work function the next

question what does this mean with

respect to how tightly electrons are

bound to an atom in which one would you

say are the electrons the most tightly

bound in which one requires would

require more energy to remove electrons

from the atom

Platinum would require the most energy

from a photon to remove electrons from

the surface of the metal because

platinum has the highest threshold

frequency and if we had to extrapolate

this graph back down to the vertical

axis it would also have the greatest

work function so in platinum the

electrons would be more tightly bound to

the atom than in potassium potassium has

the lowest threshold frequency it will

have the lowest work function therefore

it would lose electrons the easiest of

all of these metals platinum would

require the most energy to have electron

removed you may get a question involving

an electroscope an electroscope is just

an apparatus that when it is positive or

negatively charged the gold leaf will

move away from the other piece of metal

because they have the same charge

so repulsion takes place in the first

example you your electroscope can be

positive or negatively charged but so

that when red laser light is shone on it

you know that red light has got a low

frequency therefore low energy of the

photons so whether this electroscope is

positively or negatively charged it

won't have any effect so there's no

effect on the electroscope our next

electroscope is positively charged that

means that electrons have been removed

so the positive goldleaf is repelled by

the other plate which is normally zinc

or platinum so the gold leaf is repelled

by the other metal if of ultraviolet

light is shown on the positively charged

electroscope nothing happens because

ultraviolet light has a very high

frequency therefore high energy of the

photons so it can remove electrons which

would just make the electroscope more

positively charged so in this case

nothing happens there's also no effect

because your electroscope is positively

charged it has too few electrons so this

very very little chance that you're

ultraviolet light will remove more

electrons in the third example our

electroscope is negatively charged so

something was done to give it a negative

charge so the while it's negatively

charged it would look like this the gold

leaf would also be repelled by the other

metal because they both would be

negatively charged but when the

ultraviolet light with high frequency

therefore high energy is shown onto the

plate electrons will be ejected or

emitted from the electroscope so the

plate will lose those extra electrons

and the gold leaf will go down the

difference between these two is

ultraviolet light

on a positively charged electroscope it

has already lost electrons so it won't

want to lose more so it no change takes

place there in this one the electroscope

is negatively charged so in the high

frequency ultraviolet light high-energy

photons shine onto the metal electrons

will be removed so it will lose its

negative charge and the plate the gold

leaf will go down to the other metal

plate in this sketch we will be looking

at the photo cell which works under the

influence of incident light photons fall

onto the cathode electrons are emitted

and they move towards the anode and flow

through the external circuit an ammeter

or micro milli ammeter is used to

measure the current strength the cathode

is connected to the negative terminal of

the cells and the anode is connected to

the positive terminal of the cells so

your intensity of your life determines

the current strength but just remember

that the frequency of your incident

light must be greater than the threshold

frequency for electrons to be emitted an

increase in the frequency of the

incident light will increase the kinetic

energy of the emitted electrons if we

change this equation to what it is on

the right hand side all I have done is

replaced a with HF the greater the

frequency of your incident light this is

constant for the metal the greater the

kinetic energy of the electrons moving

away from the metal but if we change the

intensity of the incident light in other

words a brighter light if you increase

the intensity of the incident light that

means you have increased the number of

photons falling in on the metal this

will increase the number of electrons

emitted from the metal and that will

lead to an increase in the current

strength measured by the emitter

in the photocell so do not confuse these

two and increase in frequency with an

increase in in intensity of the