What is the work function of a metal?

[Bolter]

Homework Statement

Calculate the metal's work function

Relevant Equations

See below

Question:

I have tried this and got work function to e 5.1eV

My concern is that for these type of questions, do I need to take into account the signs of some values; such as the negative sign for the charge of an electron? Or could I just take the magnitude for all the values

Any help would be appreciated! Thanks

 

[haruspex]

Homework Statement:: Calculate the metal's work function
Relevant Equations:: See below

Question:

View attachment 258343

I have tried this and got work function to e 5.1eV

View attachment 258344

My concern is that for these type of questions, do I need to take into account the signs of some values; such as the negative sign for the charge of an electron? Or could I just take the magnitude for all the values

Any help would be appreciated! Thanks

You do need to consider signs. But the easiest way to get it right is to use simple logic. You know that the photon energy is having to overcome both the work function and the applied voltage, so you can write |hf|=[V|+|W|.

 

[vela]

It doesn't look like any of the possible answers is correct. The energy of the photon is 3.54 eV. If there is a photocurrent, the work function of the metal must be less than this.

You could save yourself a bit of time and reduce the chance of an error by spending a few minutes to learn to work with electron-volts instead of joules.

 

[Bolter]

You do need to consider signs. But the easiest way to get it right is to use simple logic. You know that the photon energy is having to overcome both the work function and the applied voltage, so you can write |hf|=[V|+|W|.

Ok noted. I’ll try to remember this the next time I stumble across a problem similar to this.

When I do use this, I get an answer of 1.99ev? Which doesn’t correlate to any of the options given to me

 

[Bolter]

It doesn't look like any of the possible answers is correct. The energy of the photon is 3.54 eV. If there is a photocurrent, the work function of the metal must be less than this.

You could save yourself a bit of time and reduce the chance of an error by spending a few minutes to learn to work with electron-volts instead of joules.

Yep have given this a try when working with electron volts and I get a value of work function to be 1.99ev; which doesn’t match up to any of the options like you have mentioned earlier