# Worksheet: The Kinetic Energy of Photoelectrons

In this worksheet, we will practice calculating the maximum possible kinetic energy of electrons that are ejected from the surface of a metal due to the photoelectric effect.

**Q1: **

Lead contained in a vacuum is illuminated with light from a laser, causing electrons to be emitted from the surface of the metal. Lead has a work function of 4.25 eV. The maximum kinetic energy of the electrons is 4.03 eV. What frequency of light does the laser emit? Use a value of eV⋅s for the value of the Planck constant.

- A Hz
- B Hz
- C Hz
- D Hz
- E Hz

**Q2: **

A polished metal surface in a vacuum is illuminated with light from a laser, causing electrons to be emitted from the surface of the metal. The light has a frequency of Hz. The work function of the metal is 1.40 eV. What is the maximum kinetic energy that the electrons can have? Use a value of eV⋅s for the Planck constant. Give your answer in electron volts.

**Q3: **

A 20.0 mW laser that produces 250 nm light is used to illuminate a block of silver. This causes electrons to be ejected from the surface of the silver. If all of the photons produced by the laser each eject one electron from the silver, what is the total current of the photoelectrons? Silver has a work function of 4.26 eV. Use a value of eV⋅s for the Planck constant and a value of C for the charge of one electron. Give your answer to 3 significant figures.

**Q4: **

A copper cathode in a vacuum chamber is illuminated with light from a laser, causing electrons to be emitted from the surface of the metal. The light has a frequency of Hz. The maximum kinetic energy of the ejected electrons is 2.80 eV. What is the work function of copper? Use a value of eV⋅s for the value of the Planck constant. Give your answer in electron volts to 3 significant figures.

**Q5: **

A 12.0 mW laser that produces 400 nm light is used to illuminate the surface of a block of sodium.

How much energy does each photon produced by the laser have? Use a value of eV⋅s for the Planck constant. Give your answer to 3 significant figures.

- A3.32 eV
- B3.11 eV
- C4.00 eV
- D1.20 eV
- E4.14 eV

How many photons are produced by the laser each second? Give your answer to 3 significant figures.

- A
- B
- C
- D
- E

Sodium has a work function of 2.28 eV. What is the maximum kinetic energy that the electrons ejected from the sodium can have?

- A2.28 eV
- B1.04 eV
- C1.86 eV
- D1.72 eV
- E0.830 eV

What is the velocity of an electron that is ejected with the maximum possible kinetic energy? Give your answer to 3 significant figures.

- A540 km/s
- B808 km/s
- C777 km/s
- D895 km/s
- E604 km/s

If all of the photons produced by the laser each eject one electron from the sodium, what is the total current of the photoelectrons? Use a value of C for the charge of one electron. Give your answer to 3 significant figures.

- A3.01 mA
- B3.62 mA
- C2.90 mA
- D3.87 mA
- E10.0 mA

**Q6: **

The graph shows the maximum kinetic energy of photoelectrons when different metals are illuminated with light of different frequencies.

Which metal has the lowest work function?

- APlatinum
- BCalcium
- CBeryllium
- DCesium
- EAluminum

Which metal has the highest work function?

- ACesium
- BPlatinum
- CCalcium
- DBeryllium
- EAluminum

**Q7: **

The graph shows the maximum kinetic energy of photoelectrons when different metals are illuminated with light of different wavelengths.

Which metal has the lowest work function?

- AUranium
- BSelenium
- CSodium
- DZinc
- ECesium

Which metal has the highest work function?

- AUranium
- BZinc
- CCesium
- DSelenium
- ESodium

**Q8: **

The diagram shows an electrical circuit. The circuit contains an anode and cathode in a vacuum chamber. The anode and cathode are connected to an ammeter and battery in series. The cathode is made of nickel.

Light of different wavelengths is used to illuminate the nickel cathode. When the wavelength of the light is shorter than 248 nm, the ammeter shows a reading of 12.8 mA. What is the work function of nickel? Use a value of eV⋅s for the Planck constant. Give your answer to 3 significant figures.

Initially, the laser used to illuminate the cathode had a power output of 64 mW. If this were increased to 128 mW, what would the current in the circuit be?

**Q9: **

A tunable laser is used to illuminate the surface of a metal with different wavelengths of light. When the wavelength of the light is shorter than a certain value, electrons are emitted from the surface of the metal. The graph shows the maximum kinetic energy of the electrons emitted against the wavelength of the photons.

What is the maximum wavelength of light for which electrons will be emitted from the surface of the metal?

What is the work function of the metal? Use a value of eV⋅s for the value of the Planck constant. Give your answer in electron volts to 3 significant figures.

**Q10: **

A tunable laser is used to illuminate the surface of a metal with different frequencies of light. Above a certain frequency of light, electrons are emitted from the surface of the metal. The graph shows the maximum kinetic energy of the electrons emitted against the energy of the photons. What is the work function of the metal?