Derive the formula for the maximum kinetic energy of an electron emitted from a metal with work function energy p , that is illuminated by light of frequency f.

MYTUTOR SUBJECT ANSWERS

Answers / Physics / A Level / Derive the formula for the maximum kinetic energy of an electron emitted from a metal with work function energy p , that is illuminated by light of frequency f.

1507 views

Derive the formula for the maximum kinetic energy of an electron emitted from a metal with work function energy p , that is illuminated by light of frequency f.

The phenomenon this question relates to is the photoelectric effect, and it can only be explained using Einstein’s photon model of light.

Electromagnetic waves are emitted in discrete lumps of energy, called photons.

The energy carried by one of these photons is given by E = hf = hc/l where l is the wavelength of the wave ( f=c/l ) , and h is the planks constant.

If a photon collides with a free electron in the surface of the metal, then the electron absorbs all of the energy of the photon. So the electron gains energy equal to hf.

However, energy is required to remove this electron from the metal. This is due to the negative charge of the electron and the positive charge of the nuclei in the metal atoms causing an attraction between them.

The energy required to remove the electron is the 'work function energy', p.

So the maximum kinetic energy that an electron can have once it has absorbed a photon and left the metal is KE = hf – p.

This is because the electron initially gains ‘hf’ of kinetic energy from the photon but then loses ‘p’ energy as it does work against the forces holding it in the metal.

George R. A Level Further Mathematics tutor, A Level Maths tutor, A ...

2 years ago

Answered by George, an A Level Physics tutor with MyTutor

Still stuck? Get one-to-one help from a personally interviewed subject specialist

147 SUBJECT SPECIALISTS

£26 /hr

James L.

Degree: Medical Sciences (Bachelors) - Exeter University

Subjects offered:Physics, Science+ 4 more

“Hi, I'm James, a Biology Masters graduate. I'm really passionate about science, and I hope i can share some of my interest with you!”

4.9

113 reviews | 295 completed tutorials

Save profile

Mabast H. GCSE Physics tutor, A Level Physics tutor, IB Physics tutor...

View profile

£20 /hr

Mabast H.

Degree: Physics (Bachelors) - Imperial College London University

Subjects offered:Physics, Maths+ 3 more

“Undergraduate Physicist with lots of experience in teaching in different fields and age groups, looking to instil a passion for learning into students.”

4.4