Question

A negatively charded metal plate is illuminated by light. Electrons escape from the metal when blue light of weak intensity is used. No electrons escape when weak or intense rad light is used. Explain. Marks Available: 6 ( including Quality of Communication marks: 2)

Answer 1

@sarah786. I can't handle these crazy question given by my crazy teacher!

Answer 2

its depend upon energy
see lambda = h / mv
energy and wavelength are inverse to each other , So blue light of shorter wavelength have more energy as Compare to red light of Longer wavelength /

Answer 3

Yes, I know that, but I'm not going to get full mark with it. I forget to write" Explain using idea of Photoelectic effect"

Answer 4

Wkipedia it http://en.wikipedia.org/wiki/Photoelectric_effect

Answer 5

my brain stops working after reading such a long passage!

Answer 6

The photoelectric equation is
\[K=hf-\Phi\]
where K is the kinetic energy of an emitted electron, h is Planck's constant, f is the frequency of the incident light, and Phi is the work function, which is the measure of how much energy it takes for an electron to be emitted. What do you notice when hf is smaller than Phi?

Answer 7

@caozeyuan ... @AllTehMaffs 'll surely help u to understand it ^^

Answer 8

@AllTehMaffs Great! you saved my Xmas!

Answer 9

^_^ Hooray! That all makes sense for what you needed?

Answer 10

That's actually called the Einstein equation, not the photoelectric equation - it's just used in the description of the photoelectric effect.

Answer 11

At least now I have something to write on my stupid "Christmas Gift of Physics Department"

Answer 12

They always give the best presents, don't they? ^_^

Answer 13

It surely is the "BEST" gift I've ever received!

Answer 14

^_^

Then for a good description of what's happening, just to add a bow on top, I have a question for you:

Can Kinetic Energy be negative?

Answer 15

@AllTehMaffs . NO! KE=1/2*m*v^2. m is positive ( how can a mass be negative!) and v^2 is positive, therefore, KE is positive

Answer 16

Correct! So that tells you something very important about the right hand side of that equation.

Answer 17

Yes, when hf-phi<0, KE becomes 0 hence no PEE

Answer 18

yup yup yup ^_^

Answer 19

Now the present is wrapped and under the tree. Happy Christmas physicsing! ^_^

Answer 20

No, I'mnot happy. I hate physics!

Answer 21

Well physics always and forever loves you.

Answer 22

I will let Physics alone and marry Biology in my university! LOL!