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International A LevelPhysicsEdexcelExam Questions2. Waves & ElectricityThe Photoelectric Effect & Atomic Spectra

The Photoelectric Effect & Atomic Spectra (Edexcel International A Level Physics)

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The Photoelectric Effect & Atomic Spectra

1a
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A gold leaf electroscope is used to demonstrate the photoelectric effect. When the zinc plate of the electroscope is given a negative charge, the conducting rod and gold leaf also become negatively charged. The gold leaf deflects away from the metal stem as shown. The deflection of the gold leaf depends on the amount of charge on the zinc plate and the conducting rod.

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A beam of ultraviolet radiation is incident on the zinc plate. The gold leaf immediately begins to fall back to the conducting rod.

Explain why this observation cannot be explained by the wave model of electromagnetic radiation.

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1b
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Photons of ultraviolet radiation with an energy of 9.3 × 10−19 J are directed towards the zinc plate.

i) Calculate the maximum speed with which electrons are released from the plate.

work function of zinc = 4.3 eV

Maximum speed of electrons = ........................................(4)

ii) A student suggests that a greater maximum speed of electrons could have been achieved if both:

– a metal with a lower work function than zinc was used

– ultraviolet radiation with a greater wavelength was used.

Discuss the student’s suggestion.

(3)

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2a
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After an atom of hydrogen has been exposed to suitable electromagnetic radiation, the atom can emit visible light. The emitted light contains a small number of different wavelengths of visible light.

Explain the process that results in the emission of different wavelengths of visible light. Your answer should include reference to energy levels in atoms.

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2b
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It is also possible to make the atoms in a sample of air emit visible light.

Explain why the light emitted by the air has a large number of different wavelengths.

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3a
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A student used two sources, A and B, of electromagnetic radiation to investigate the photoelectric effect. Radiation from A has a photon energy of 2.0 eV.

The radiation from B has a wavelength of 280 nm.

Show that this radiation has a photon energy of about 4.4 eV.

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3b
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*The student used the two sources of radiation to investigate the photoelectric effect for two different metals, copper and zinc.

The following statements were made by the student.

When radiation of photon energy 2.0 eV from source A is directed towards either of the metal plates no electrons are released, even when the intensity of the radiation is increased.

When radiation of photon energy 4.4 eV from source B is directed towards the copper plate, no electrons are released. However, when the radiation is directed towards the zinc plate, electrons are released. As the intensity of radiation is increased, electrons are released at a greater rate.

Explain the conclusions that can be made from these statements.

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4
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* In the early 20th century, observations of the photoelectric effect demonstrated that light behaves as a particle.

Explain how observations from the photoelectric effect demonstrate the particle nature of light.

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