Page 382 - Physics Coursebook 2015 (A level)

Cambridge International A Level Physics
7 An α-particle emitted in the radioactive decay of radium has a kinetic energy of 8.0 × 10−13 J.
a i Calculate the potential difference that an α-particle, initially at rest, would have to be accelerated
through to gain this energy. [2] ii Calculate the speed of the α-particle at this kinetic energy. [3]
b Figure 23.20 shows the path of an α-particle of this energy as it approaches a gold nucleus head-on.
α-particle
gold nucleus
Figure 23.20 For End-of-chapter Question 7.
i State the speed of the α-particle at its point of closest approach to the gold nucleus. [1]
ii Write down the kinetic energy of the α-particle at this point. [1]
iii Write down the potential energy of the α-particle at this point. [1]
c Use your answer to b iii to show that the α-particle will reach a distance of 4.5 × 10−14 m from the
centre of the gold nucleus. [2] d Suggest and explain what this information tells us about the gold nucleus. [2]
(Mass of an α-particle = 6.65 × 10−27 kg, charge on an α-particle = +2e, charge on a gold nucleus = +79e.)
8 a
b Figure 23.21 shows the potential well near a hydrogen nucleus.
Define electric potential at a point. [2] The first electron orbital can be considered to be a circle of diameter 1.04 × 10−10 m.
5 V /V
0.5 1.0 1.5 2.0 2.5
–5
–10
–15
–20
–25
–30
Figure 23.21 For End-of-chapter Question 8.
i Determine the potential at a point on this orbital. [2]
ii Calculate the energy required to ionise the atom. [2]
c Use the graph to estimate the electric field strength at a distance of 1.0 × 10−10 m from the centre
of the nucleus. [2]
–2.5 –2.0 –1.5 –1.0 –0.5
r/m × 10–10
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