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Question 18N.3.HL.TZ0.6

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Date November 2018 Marks available [Maximum mark: 5] Reference code 18N.3.HL.TZ0.6
Level HL Paper 3 Time zone TZ0
Command term Calculate, Explain, Show that Question number 6 Adapted from N/A
6.
[Maximum mark: 5]
18N.3.HL.TZ0.6

An electron with total energy 1.50 MeV collides with a positron at rest. As a result two photons are produced. One photon moves in the same direction as the electron and the other in the opposite direction.

(a)

Show that the momentum of the electron is 1.41 MeV c–1.

[1]

Markscheme

p c = E 2 − ( m c 2 ) 2 = 150 2 − 0.511 2  «= 1.410 MeV» ✔

The momenta of the photons produced have magnitudes p1 and p2. A student writes the following correct equations.

p1 – p2 = 1.41 MeV c–1

p1 + p2 = 2.01 MeV c–1

(b.i)

Explain the origin of each equation.

[2]

Markscheme

first equation is due to momentum conservation ✔

second equation is due to total energy conservation ✔

(b.ii)

Calculate, in MeV c–1, p1 and p2.

[2]

Markscheme

adding 2p1 = 3.42 MeV c–1 ⇒ p1 = 1.17 MeV c–1 ✔

p2 = 0.30 MeV c–1 ✔

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