Photoelectric effect, Stopping voltage, Kinetic energy max... IMPORTANT!! (2 Viewers)

[Lucas_]

Hey,

So I'm still trying to wrap my ahead around the idea of the photoelectric effect. I've used two different text books but I am still struggling with the following ideas:

• Stopping Voltage (V_stop)
  
• Maximum Kinetic Energy (E_KMax)
• Work function (Phi)
• Threshold frequency

Basically, my understanding of the photoelectric effect so far is that a sheet of metal can emit electrons when exposed to EMR like UV light. These electrons are collected by a collector plate, with the resultant movement of electrons allowing current to flow through a circuit. This current is then measured by a meter. If the collector plate is made negative (how?) then the photocurrent will be zero (as negative electrons unwilling to flow to negative plate). Different coloured lights being shone on the metal (ie, different wavelengths) affect the electrons differently by providing them with varying levels of energy (again, how?) to overcome the negative potential.

I don't understand where the aforementioned terms come into my very basic understanding, nor what they even mean. If somebody could please help, I'll rep them x 2 if the system ever comes back!

 

[nightweaver066]

Hey,

So I'm still trying to wrap my ahead around the idea of the photoelectric effect. I've used two different text books but I am still struggling with the following ideas:

• Stopping Voltage (V_stop)
  
• Maximum Kinetic Energy (E_KMax)
• Work function (Phi)
• Threshold frequency

Basically, my understanding of the photoelectric effect so far is that a sheet of metal can emit electrons when exposed to EMR like UV light. These electrons are collected by a collector plate, with the resultant movement of electrons allowing current to flow through a circuit. This current is then measured by a meter. If the collector plate is made negative (1. how?) then the photocurrent will be zero (as negative electrons unwilling to flow to negative plate). Different coloured lights being shone on the metal (ie, different wavelengths) affect the electrons differently by providing them with varying levels of energy (2. again, how?) to overcome the negative potential.

I don't understand where the aforementioned terms come into my very basic understanding, nor what they even mean. If somebody could please help, I'll rep them x 2 if the system ever comes back!

1. By applying a potential (connecting a power pack or battery)

2. Light is made up of photons each carrying a quanta of energy proportional to frequency, E = hf
Also, c = f(lambda), but c is constant, so varying the wavelength will change frequency which changes energy.
So putting it all together,
Light of higher energy will give electrons a greater kinetic energy allowing it to overcome the opposing force by the potential.

Stopping voltage: The voltage YOU must APPLY (battery / power pack or something) that prevents electrons from reaching the anode (the work it exerts is greater than the maximum kinetic energy of electrons). No electron reaching anode = no electron flow.

Maximum kinetic energy: The name speaks for itself; the maximum kinetic energy of a photoelectron (an electron emitted by the photoelectric effect)

Work function: The MINIMUM amount of energy required for an electron to be released from a metal.

Threshold frequency: The MINIMUM frequency of a photon, that would carry energy equivalent to the WORK FUNCTION causing an electron to be emitted.

 

[jamesischool]

also the maximum kinetic energy of emitted photoelectrons is equal to E = hf - the work function required to emit electrons from the metal

 

[nightweaver066]

also the maximum kinetic energy of emitted photoelectrons is equal to E = hf - the work function required to emit electrons from the metal

Typing that up nicer

 

[jamesischool]

Typing that up nicer

thanks haha I'm not too skilful with the text creating thing

 

[Lucas_]

Thanks guys

If rep comes back you can have some

 

[jamesischool]

no idea what rep is...

 

[Lucas_]

Could either of you guys go over threshold frequency again? Not understanding that

 

[nightweaver066]

Could either of you guys go over threshold frequency again? Not understanding that

So the work function is the minimum energy required for an electron to be emitted by the metal.

This energy can be supplied by a photon (as photons carry energy proportional to frequency by E = hf)

The minimum frequency at which this energy can be attained (to supply/overcome the work function) is the threshold frequency.

 

[jamesischool]

say for example the work function of a metal was 10 joules and that planck's constant (h) is equal to 2. the minimum frequency required to reach the work function of 10 would be
E=hf
10=2(f)
f=5
the threshold frequency required for electron to be emitted is equal to 5 Hertz. this is really simplified but its easy to explain that way
feel free to keep asking questions it helps me learn too

 

[Lucas_]

Thanks guys

I totally understand the photoelectric effect now - It's actually pretty simple once you get your head around it!

 

[OperatingTheatres]

wow awesome cooperation here. thanks guys your simplified explanation helped me in my next lab (the photoelectric effect)