# Threshold frequency(quantum phenomena)

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thefatone

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#1

https://00c07169b8f01b5b433281e611ee...%20Physics.pdf

question 2c

i have

and that's it i have no idea what to do from there

i also know that

question 2c

i have

and that's it i have no idea what to do from there

i also know that

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thefatone

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#2

samb1234

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#3

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#3

(Original post by

help?

**thefatone**)help?

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thefatone

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#4

(Original post by

Start by calculating the work function, and see if you can go from there (or there is a shortcut because of the values they have used)

**samb1234**)Start by calculating the work function, and see if you can go from there (or there is a shortcut because of the values they have used)

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samb1234

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#5

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#6

(Original post by

Think about how the work function relates to the threshold frequency

**samb1234**)Think about how the work function relates to the threshold frequency

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samb1234

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#7

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#7

(Original post by

work function is half the value of frequency isn't it?

**thefatone**)work function is half the value of frequency isn't it?

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#8

(Original post by

no. E=hf

**samb1234**)no. E=hf

and E=hf doesn't have in it :/

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Someboady

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#9

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#9

(Original post by

work function is half the value of frequency isn't it?

**thefatone**)work function is half the value of frequency isn't it?

E (work function) = h (planck's constant) * f0 (Threshold Frequency)

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Someboady

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#11

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#11

thus for this question:

first calculate work function

workfunction = hf (where f is threshold frequency of 5.6 * 10^14)

thus workfunction is something you can calculate (my calculator is under my bed xD)

therefore

Ekmax = work function - (2*5.6 × 10^14) - since frequency is twice the threshold frequency

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The-Spartan

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#12

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#12

You know right? so

is the best start, calculating the energy of the incoming photons.

. This is the total energy of the incoming photons yes?

Now not all this energy goes into the kinetic energy of the electron. Remember, some of it goes into liberating it. The energy needed for this is the work function energy.

for the energy needed at the work function, we know where is the threshold frequency.

I think this is where you are confused. Work function of a metal is the

**energy**required to liberate an electron. Not the threshold frequency, which is just the minimum frequency of an incoming photon to have the energy equal to the work function.

Back to the first equation:

therefore

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#13

(Original post by

Ekmax = work function - hf (where f is threshold frequency)

thus for this question:

first calculate work function

workfunction = hf (where f is threshold frequency of 5.6 * 10^14)

thus workfunction is something you can calculate (my calculator is under my bed xD)

therefore

Ekmax = work function - (2*5.6 × 10^14) - since frequency is twice the threshold frequency

**Someboady**)Ekmax = work function - hf (where f is threshold frequency)

thus for this question:

first calculate work function

workfunction = hf (where f is threshold frequency of 5.6 * 10^14)

thus workfunction is something you can calculate (my calculator is under my bed xD)

therefore

Ekmax = work function - (2*5.6 × 10^14) - since frequency is twice the threshold frequency

(Original post by

You're pretty much there

You know right? so

is the best start, calculating the energy of the incoming photons.

. This is the total energy of the incoming photons yes?

Now not all this energy goes into the kinetic energy of the electron. Remember, some of it goes into liberating it. The energy needed for this is the work function energy.

for the energy needed at the work function, we know where is the threshold frequency.

I think this is where you are confused. Work function of a metal is the

Back to the first equation:

therefore

**The-Spartan**)You're pretty much there

You know right? so

is the best start, calculating the energy of the incoming photons.

. This is the total energy of the incoming photons yes?

Now not all this energy goes into the kinetic energy of the electron. Remember, some of it goes into liberating it. The energy needed for this is the work function energy.

for the energy needed at the work function, we know where is the threshold frequency.

I think this is where you are confused. Work function of a metal is the

**energy**required to liberate an electron. Not the threshold frequency, which is just the minimum frequency of an incoming photon to have the energy equal to the work function.Back to the first equation:

therefore

On this particular question op you don't have to actually calculate the work function separately. Either way will work but algebraically if we know that f=2 f0 then we have Ek=2hf0 -hf0 =hf0, which is neater as it avoids any potential errors from rounding earlier on in the question (spartan's answer should really be 3.71, but by using rounded numbers earlier we end up with a slight rounding error, although you would still probably get the mark in the exam)

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The-Spartan

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#14

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#14

(Original post by

[/b]

On this particular question op you don't have to actually calculate the work function separately. Either way will work but algebraically if we know that f=2 f0 then we have Ek=2hf0 -hf0 =hf0, which is neater as it avoids any potential errors from rounding earlier on in the question

**samb1234**)[/b]

On this particular question op you don't have to actually calculate the work function separately. Either way will work but algebraically if we know that f=2 f0 then we have Ek=2hf0 -hf0 =hf0, which is neater as it avoids any potential errors from rounding earlier on in the question

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#15

(Original post by

True, but this only works in specific questions. I find it nicer to run through the set algorithm for kinetic energy shortcuts loose me marks all the time

**The-Spartan**)True, but this only works in specific questions. I find it nicer to run through the set algorithm for kinetic energy shortcuts loose me marks all the time

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#16

(Original post by

Work function relates to the threshold frequency by

E (work function) = h (planck's constant) * f0 (Threshold Frequency)

**Someboady**)Work function relates to the threshold frequency by

E (work function) = h (planck's constant) * f0 (Threshold Frequency)

(Original post by

**samb1234**)**Work function is the minimum amount of energy required to liberate a photon, and we know that the threshold frequency is the minimum frequency required to liberate a photon.**Therefore thew ork function =h x threshold frequencyis

where

E= energy of photon in joules <--- how does that become the work function?? i don't understand

any formula working out and substitutions required pls i don't understand :/

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lerjj

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#17

(Original post by

i'm pretty sure E=hf

is

where

E= energy of photon in joules <--- how does that become the work function?? i don't understand

any formula working out and substitutions required pls i don't understand :/

**thefatone**)i'm pretty sure E=hf

is

where

E= energy of photon in joules <--- how does that become the work function?? i don't understand

any formula working out and substitutions required pls i don't understand :/

2)The work function is the energy needed to liberate a photon

3)If you shine a light of double threshold frequency, then half will be used to overcome the work function

So the remaining energy is the kinetic energy, which is just of the incident light.

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Someboady

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#18

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#18

**thefatone**)

i'm pretty sure E=hf

is

where

E= energy of photon in joules <--- how does that become the work function?? i don't understand

any formula working out and substitutions required pls i don't understand :/

Threshold frequency is the minimum frequency of light required for electrons to be emitted from the metal.

Work function is the minimum amount of energy required for an electron to be emitted from the surface of a metal.

So if you link the two... The threshold frequency provides the work function right?

Thus the photon that is absorbed must have energy equal to the work function for the electron to be emitted. and we know work function and threshold frequency are linked

So we can say that the energy of the photon must have a minimum energy = h * threshold frequency i.e. E = hf. And we know that the minimum energy is the work function so:

work function = h*threshold frequency. This is a general rule. Learn this formula.

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#19

(Original post by

Okay so basically... What is work function. What is threshold frequency

Threshold frequency is the minimum frequency of light required for electrons to be emitted from the metal.

Work function is the minimum amount of energy required for an electron to be emitted from the surface of a metal.

So if you link the two... The threshold frequency provides the work function right?

Thus the photon that is absorbed must have energy equal to the work function for the electron to be emitted. and we know work function and threshold frequency are linked

So we can say that the energy of the photon must have a minimum energy = h * threshold frequency i.e. E = hf. And we know that the minimum energy is the work function so:

**Someboady**)Okay so basically... What is work function. What is threshold frequency

Threshold frequency is the minimum frequency of light required for electrons to be emitted from the metal.

Work function is the minimum amount of energy required for an electron to be emitted from the surface of a metal.

So if you link the two... The threshold frequency provides the work function right?

Thus the photon that is absorbed must have energy equal to the work function for the electron to be emitted. and we know work function and threshold frequency are linked

So we can say that the energy of the photon must have a minimum energy = h * threshold frequency i.e. E = hf. And we know that the minimum energy is the work function so:

**work function = h*threshold frequency**. This is a general rule. Learn this formula.
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#20

(Original post by

You're pretty much there

You know right? so

is the best start, calculating the energy of the incoming photons.

. This is the total energy of the incoming photons yes?

Now not all this energy goes into the kinetic energy of the electron. Remember, some of it goes into liberating it. The energy needed for this is the work function energy.

for the energy needed at the work function, we know where is the threshold frequency.

Back to the first equation:

therefore

**The-Spartan**)You're pretty much there

You know right? so

is the best start, calculating the energy of the incoming photons.

. This is the total energy of the incoming photons yes?

Now not all this energy goes into the kinetic energy of the electron. Remember, some of it goes into liberating it. The energy needed for this is the work function energy.

for the energy needed at the work function, we know where is the threshold frequency.

**I think this is where you are confused**. Work function of a metal is the**energy**required to liberate an electron. Not the threshold frequency, which is just the minimum frequency of an incoming photon to have the energy equal to the work function.Back to the first equation:

therefore

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