PHOTOELECTRIC EFFECT

Question 1

Talk abt how the gold leaf electroscope works

Answer 1

1. System is og uncharged
2. System becomes charged by adding electrons
3. Electrons flow through system. Gold leaf repelled as same charge as apparatus
4. If visible light on plane, nothing happens
5. If UV light on plane, gold leaf drops
6. High freq. = electrons are liberated, no more same charge

Question 2

Why did the leaf fall from the UV light?

Answer 2

• light behaves as a particle known as a photon (a packet of energy)
• energy of a photon is directly proportional to freq. of a wave (Ephoton = hf) (h = Planck’s constant) (Ephoton = h(c/y))

Question 3

What is the work function and explain how it is relevant and give equation

Answer 3

• The minimum energy needed to liberate an electron
• the excess photon energy will transfer to the electron’s Ek
• diff metals = diff work functions
• if energy of photon < work function, no electrons are liberated

Hf = WF + Ek

Question 4

How does diff intensity & freq. affect the PE effect

Answer 4

Higher intensity = higher number of photons arriving = more electrons emitted per second = leaf falls faster
Does not change KE of emitted electron

Higher frequency = more energy given as kinetic energy = WF is constant = number of photons emitted is the same

Question 5

What is threshold freq and give equation

Answer 5

fo = minimum freq. of photon needed to liberate electron from metal surface
Hfo = WF

Question 6

Ek vs freq graph

Answer 6

Y intercept = -WF
Grad = Planck’s constant
X intercept = fo