# I need help on these questions ! Nature of light

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#1
I need help on these questions
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#2
(Original post by Imrankhan0121)
I need help on these questions
Question b and c
And question is number 2

I worked out yeah old frequency and it is 5.5*10^14

How would u work it out ( energy of photon)

And potential difference
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#3
The images don't work so I'll write it

When blue light of wavelength 447 bm is shone onto a sodium surface , photoelectrons are emitted . The work function of sodium is 3.28eV

The tresholf frequency is 5.5 *10^14 I worked it out

The energy of photons of the blue light 2.78eV worked it out

Now c is hard for me .
The potential diff that would have to be applied to just prevent photoelemission would be

I don't know where to start
Help
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6 years ago
#4
(Original post by Imrankhan0121)
The images don't work so I'll write it

When blue light of wavelength 447 bm is shone onto a sodium surface , photoelectrons are emitted . The work function of sodium is 3.28eV

The tresholf frequency is 5.5 *10^14 I worked it out

The energy of photons of the blue light 2.78eV worked it out

Now c is hard for me .
The potential diff that would have to be applied to just prevent photoemission would be

I don't know where to start
Help
First find the maximum kinetic energy of the photoelectrons in this case. (Use Einstein's Equation)

To prevent them you need to apply a negative electric potential V such that a charge e would lose all that kinetic energy in overcoming that potential. That is, they would be brought to rest.

So equate
max. kinetic energy to eV
eV is the work done by the applied electric field in stopping the electrons.

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#5
(Original post by Stonebridge)
First find the maximum kinetic energy of the photoelectrons in this case. (Use Einstein's Equation)

To prevent them you need to apply a negative electric potential V such that a charge e would lose all that kinetic energy in overcoming that potential. That is, they would be brought to rest.

So equate
max. kinetic energy to eV
eV is the work done by the applied electric field in stopping the electrons.

Why would finding the max velocity to find voltage
I haven't got mass of particle
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6 years ago
#6
(Original post by Imrankhan0121)
Why would finding the max velocity to find voltage
I haven't got mass of particle
You have the mass of an electron given to you in the formulae book?
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6 years ago
#7
(Original post by Imrankhan0121)
Why would finding the max velocity to find voltage
I haven't got mass of particle
You don't need that.

You have the max kinetic energy of the electrons from applying the Einstein equation with work function and the photon energy.
Equate that to eV to find V.

Read my 1st post again. I explained why this finds the voltage.

key words
. kinetic energy
. work done by an electric field = eV
. work done by field stops the electron and removes its kinetic energy

Do you understand the idea of work and energy?
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#8
Ok thanks
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#9
The question gave me no velocity dude
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#10
im confused help still
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