DP Physics (first assessment 2025)

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Question 19N.2.HL.TZ0.11

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Date November 2019 Marks available [Maximum mark: 9] Reference code 19N.2.HL.TZ0.11
Level HL Paper 2 Time zone TZ0
Command term Calculate, Draw, Explain Question number 11 Adapted from N/A
11.
[Maximum mark: 9]
19N.2.HL.TZ0.11

Monochromatic light of very low intensity is incident on a metal surface. The light causes the emission of electrons almost instantaneously. Explain how this observation

In an experiment to demonstrate the photoelectric effect, light of wavelength 480 nm is incident on a metal surface.

The graph shows the variation of the current I in the ammeter with the potential V of the cathode.

(a(i))

does not support the wave nature of light.

[2]

Markscheme

«low intensity light would» transfer energy to the electron at a low rate/slowly ✔
time would be required for the electron «to absorb the required energy» to escape/be emitted ✔

NOTE: OWTTE

(a(ii))

does support the photon nature of light.

[2]

Markscheme

«in the photon theory of light» the electron interacts with a single photon ✔
and absorbs all the energy OR and can leave the metal immediately ✔

NOTE: Reference to photon-electron collision scores MP1

(b(i))

Calculate, in eV, the work function of the metal surface.

[3]

Markscheme

ϕ=hcλ-EK ✔

EK=1.5«eV» ✔

ϕ=«1.24×10-6480×10-9-1.5=» 1.1 «eV»✔

NOTE: Allow reading from the graph of Ek=1.4leading to an answer of 1.2 «eV».

(b(ii))

The intensity of the light incident on the surface is reduced by half without changing the wavelength. Draw, on the graph, the variation of the current I with potential V after this change.

[2]

Markscheme

similar curve lower than original ✔

with same horizontal intercept ✔

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