2.4 The Photoelectric Effect

Photons are incident on a metal plate and electrons are released via photoelectric emission. Which graph shows the relationship between the maximum kinetic energy E_k of the photoelectrons and the wavelength  of the incident light?

A zinc surface with a work function of 4.3 eV and area of 10 cm² is charged to –5.0 mC then illuminated with an ultraviolet lamp. The lamp has an output power of 100 W and a frequency of 1.2 × 10¹⁵ Hz.

The lamp is positioned 30 cm above the surface. How long does it take for the zinc surface to become electrically neutral?

Assume that the UV light is incident normally on the zinc surface.

A monochromatic light source with wavelength λ illuminates a metal surface with function . Photoelectrons are emitted.

 Which of the following correctly relates the de Broglie wavelength of emitted photoelectrons, λ_e , to the wavelength of incident light λ ?

Visible light with wavelength  illuminates a clean sodium surface with work function 2.3 eV. Photoelectrons are emitted with a de Broglie wavelength equal to the wavelength of the incident light, .

 What is the wavelength of the incident light?

A semiconductor chip is used to store information. The information can only be erased by exposing the chip to ultraviolet (UV) light.

 A recycling company is setting up a production line to erase silicon chips that have a work function of 4.03 eV. They need to choose a UV source that meets the following requirements:

 Which machine should the company choose?

A vacuum photocell is connected to in series with a power supply, a variable resistor, and a sensitive ammeter. A voltmeter is connected in parallel across the photocell.

Monochromatic light of frequency illuminates the cathode, which has a threshold frequency . Photoelectrons are emitted and collected by the anode. A photocurrent is measured by the ammeter.

The potential difference across the photocell, , is increased until the ammeter reads zero.

Which of the equations below does not correctly relate the potential at which the current decreases to zero to the threshold frequency  and frequency ?

A vacuum photocell with work function  is illuminated by ultraviolet (UV) sources of frequency  and  (both above the threshold frequency), and the stopping potentials  and  are measured for each.

If , what is the ratio ?

Ultraviolet light with a wavelength of 240 nm falls on curved electrode of a vacuum photocell. The curved electrode has a work function of 3.2 eV. Electrons are emitted from the electrode surface with a range of kinetic energies. The stopping potential of the most energetic electron is  The distance between the electrodes is 3.6 cm.

The potential difference between the electrodes varies from , when curved electrode is positively charged, to , when its polarity reverses, with a frequency of 1 kHz.

Consider an electron that is emitted from the curved electrode when the potential just changes to . Take its kinetic energy to be equal to half the maximum kinetic energy.

What is the de Broglie wavelength of this electron by the time it reaches the other electrode?

In an experiment to demonstrate the photoelectric effect, a charged metal plate is illuminated with light from different sources. The plate loses charge when an ultraviolet light source is used but not when a red light source is used.

What is the reason for this?

A beam of light of wavelength λ is incident on a clean metal surface and photoelectrons are emitted. The wavelength of the light is doubled but energy incident per second is kept the same.

Which row in the table is correct?

Monochromatic light from light source A illuminates a metal surface and electrons are emitted from the surface. When light source B illuminates the same surface, no electrons are emitted.

Which property of the radiation from source A must be greater than that from source B?

Light is incident on a metal surface and causes emission of photoelectrons. These flow in a circuit as a photocurrent.

Which of the following is not an observed effect?  

When a metal in a vacuum is irradiated with UV radiation, electrons are emitted.

What would be the effect on the stopping potential and the photocurrent if the intensity of the ultraviolet radiation is increased?

What is the maximum speed of emitted photoelectrons from a metal surface with a stopping potential of 5 mV?

A monochromatic beam of red light falls on one electrode of a photocell and electrons are emitted.

The light beam is then replaced by a blue beam delivering the same energy per unit time to the cell.

Which one of the following quantities decreases as a result of this change?

The results of the photoelectric effect can be investigated by plotting a graph of maximum kinetic energy of emitted electrons  with frequency of incident light f on a metal surface.

Which of the lines, A to D, is not a possible result of the photoelectric effect?