GREPhysics.NET: GR9677 #42

GR9677 #42

Problem

GREPhysics.NET Official Solution

This problem is still being typed.

Quantum Mechanics $\Rightarrow$ }Photoelectric Effect

Recall the photoelectric equation relating the incident electromagnetic wave to the kinetic energy and the work function $hc/\lambda = K+\phi \ approx 12E-7/500E-9 = K+2.28 \Rightarrow K = 12E-7/5E-7-2.28\approx 0.2 eV$ , as in choice (B).

Alternate Solutions

cczako
2013-10-18 15:36:40

Remember KE=E-phi where E is the energy of the light and phi is the workfunction. Don't forget that E=hc/lambda and that hc can be written as 1240 nm*eV. That means that 500 nm is about 2.5 eV so KE is simply 2.5 -2.28 which is 0.22 eV or choice B.

Reply to this comment

Comments

cczako
2013-10-18 15:36:40

Reply to this comment

Dodobird
2010-11-12 14:46:11

We get E = .12 eV, which doesn't really help us differentiate between choice A and B. There is a difference of .01 eV in 'closeness' to these answers. In fact the wording of the problem would suggest our maximum energy can only be .03 eV out of the choices given.
Help?

pam d
2011-09-15 21:55:01

I know this is way too late but you actually get $\frac{1240}{500}=2.5eV$ (a reasonable mental calculation). The difference between this and the work function gives the maximum possible KE, which puts you at about $0.22 eV$ .

Reply to this comment

CarlBrannen
2010-10-07 14:14:11

Use h-bar c = 1240 nm eV. Converting 500nm, we get 2.48 eV. Subtracting 2.28 eV for the work function, we find 0.2 eV, answer (B).

Reply to this comment

vortex
2005-12-05 15:50:02

As a twist of fate!, the formula is given in question 27.

Reply to this comment

Post A Comment!

You are replying to:

Use h-bar c = 1240 nm eV. Converting 500nm, we get 2.48 eV. Subtracting 2.28 eV for the work function, we find 0.2 eV, answer (B).

Bare Basic LaTeX Rosetta Stone
LaTeX syntax supported through dollar sign wrappers $, ex., $\alpha^2_0$ produces $\alpha^2_0$ .
type this...	to get...
$\int_0^\infty$	$\int_0^\infty$
$\partial$	$\partial$
$\Rightarrow$	$\Rightarrow$
$\ddot{x},\dot{x}$	$\ddot{x},\dot{x}$
$\sqrt{z}$	$\sqrt{z}$
$\langle my \rangle$	$\langle my \rangle$
$\left( abacadabra \right)_{me}$	$\left( abacadabra \right)_{me}$
$\vec{E}$	$\vec{E}$
$\frac{a}{b}$	$\frac{a}{b}$

The Sidebar Chatbox...
Scroll to see it, or resize your browser to ignore it...

All-Solutions List | Latest Comments | Unanswered Questions (Cries for Help!) |::| About

This site is not affiliated with ETS, nor is it officially endorsed (yet) by ETS. This site is the work of an individual named Yosun Chang. The solutions, sans user comments and ETS questions, are © 2005 by Yosun Chang except where noted. All rights reserved. / The comments appending particular solutions are due to the respective users. / Educational Testing Service, ETS, the ETS logo, Graduate Record Examinations, and GRE are registered trademarks of Educational Testing Service. The examination questions are © 1997 and © 2001 by ETS.

Bare Basic LaTeX Rosetta Stone