A-LevelPhysicsQuantum physics9702/41 · May/June 2019 · Q1111 Marks

State three pieces of evidence provided by the photoelectric effect for a particulate nature of electromagnetic radiation.

(a)State three pieces of evidence provided by the photoelectric effect for a particulate nature of electromagnetic radiation.[3]
(b)(i)The work function energies of some metals are shown in Fig. 11.1. [Figure 11.1] Each metal is irradiated with electromagnetic radiation of wavelength 380 nm. Calculate the energy, in eV, of a photon of electromagnetic radiation of wavelength 380 nm.[3]
(b)(ii)Determine which metals will give rise to the emission of photoelectrons. Explain your answer.[2]
(c)Photons of wavelength 380 nm are incident normally on a metal surface at a rate of 7.6 x 10^14 s^–1. All the photons are absorbed in the surface and no photoelectrons are emitted. Calculate the force exerted on the metal surface by the incident photons.[3]

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[3] Any three points from: • (max) energy of emitted electrons depends on frequency • (max) energy of emitted electrons does not depend on intensity • rate of emission of electrons depends on intensity (at constant frequency) • existence of frequency below which no emission of electrons • instantaneous emission of electrons • increasing the frequency at constant intensity decreases the rate of emission of electrons
[1] photon energy = hc/λ
[1] = (6.63 × 10⁻³⁴ × 3.0 × 10⁸) / (380 × 10⁻⁹)
[1] (= 5.23 × 10⁻¹⁹ J)
[1] = 3.3 eV
[1] photon energy must be greater than work function (energy)
[1] so sodium and calcium
[1] λ = h/p
[1] p = (6.63 x 10⁻³⁴) / (380 × 10⁻⁹) = 1.74 x 10⁻²⁷ N s
[1] force = 1.74 × 10⁻²⁷ x 7.6 x 10¹⁴ = 1.3 x 10⁻¹² N

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