# Photoelectric Effect

1. Nov 22, 2009

### Cursed

1. The problem statement, all variables and given/known data

The work function of chromium metal is 7.2 x 10-19 J. What is the maximum speed an electron can be moving if it is ejected from chromium metal by light of wavelength 250 nm? (Answer: u= 4 x105 m/s)

2. Relevant equations

$$\Phi = h v_{0}$$

$$KE = h v_{light} - \Phi = \frac{m_{e} u^{2}_{e}}{2}$$

$$\Delta E_{light}= \Phi + KE$$

$$h$$ is Planck's constant
$$v_{0}$$ is the characteristic frequency
$$m_e$$ is the mass of an electron (9.1 x 10-31 kg)
$$u_e$$ is the speed of the electron

3. The attempt at a solution

$$7.2\times10^{-19} J = \frac{(9.1\times10^{-31} kg) (u^{2}_{e})}{2}$$

$$u_e \approx 1.3 \times 10^6 m/s$$

Last edited: Nov 22, 2009
2. Nov 27, 2009

### Redbelly98

Staff Emeritus
Keep this equation in mind.

You have left out the energy of the photon, the hvlight in your earlier equation.