Photoelectric effect & your home

[accountkiller]

If the photoelectric effect causes light to knock electrons out of metals, why don't the metal surfaces in our home lose electrons when we turn on the light?

I'm a third-year college student. This question was a discussion question in the back of the chapter, and I thought it was a great question but I have no idea what the explanation is.

Why is it that metals at home don't lose their electrons because of our light?

 

[ZapperZ]

Why don't you start by asking why don't the metal, which act as a photocathode, in a standard photoelectric effect experiment, lose electrons? After all, if anything will clearly lose electrons, that photocathode will.

Upon closer examination of the circuit, one will realize that the photocathode tends to be grounded. This means that it has a plentiful supply of electrons, preventing a charging effect.

Now, take a lot at the metals in your home. These metals, especially those connected to your appliances, or large large metal objects, are typically either grounded or connected to some other large objects that will ground it.

Or, the light source that you are using may not have enough energy to cause a photoemission, if the work function is too high. After all, metals like copper has a work function of around 4.7 eV. This is in the UV range, way higher than your typical visible light energy.

Zz.

 

[Upisoft]

If the photoelectric effect causes light to knock electrons out of metals, why don't the metal surfaces in our home lose electrons when we turn on the light?

I'm a third-year college student. This question was a discussion question in the back of the chapter, and I thought it was a great question but I have no idea what the explanation is.

Why is it that metals at home don't lose their electrons because of our light?

They do lose electrons.

 

[NobodySpecial]

They do lose electrons.

And the surface normally has air around it so any lost electrons are quickly replaced.

 

[accountkiller]

Zz, I'm not sure what you mean by the metal being grounded and "uncharged" as a reason for why the electrons aren't lost... even if the metal is grounded, the light still evokes the electron out, does it not?

Upisoft & NobodySpecial, that is the theory my dad came up with to try to explain to me - that as soon as the electrons escape by photoemission, they are immediately drawn back in, so it's like a never-ending process. Why are they immediately drawn back in? Is it because the light doesn't give it too much kinetic energy to escape any farther than just right above the surface?

NobodySpecial, how does the air interact with the electrons to make them go back to the metal?

 

[Upisoft]

Zz, I'm not sure what you mean by the metal being grounded and "uncharged" as a reason for why the electrons aren't lost... even if the metal is grounded, the light still evokes the electron out, does it not?

When a metal is grounded the Earth itself acts as huge source of electrons. So in this case Earth successfully gains small positive charge. Even if this happens a lot you will see no big charge in the metal object.

Upisoft & NobodySpecial, that is the theory my dad came up with to try to explain to me - that as soon as the electrons escape by photoemission, they are immediately drawn back in, so it's like a never-ending process. Why are they immediately drawn back in? Is it because the light doesn't give it too much kinetic energy to escape any farther than just right above the surface?

I think that both cases are possible. If electron returns it will do that because the Earth(and the metal object) are positively charged compared to the atmosphere. In the second case the electron will probably find positive ion in the atmosphere and recombine.