CIE iGCSE Co-Ordinated Science P2.1.2 Particle model Exam Style Questions Paper 4
Question
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P2.1.2 — Particle model / Gas pressure (Part (a)(i))
• Topic P2.1.2 — Particle model / Temperature and particle motion (Part (a)(ii))
• Topic P2.1.3 — Pressure changes / Gas laws (Part (a)(iii))
• Topic P3.4 — Sound / Speed of sound in different media (Part (b)(i))
• Topic P3.4 — Sound / Ultrasound definition (Part (b)(ii))
• Topic P3.4 — Sound / Ultrasound calculations (Part (b)(iii))
▶️ Answer/Explanation
(a)(i) Gas pressure is caused by the collisions of particles with the walls of the container.
Gas particles move randomly in all directions, constantly colliding with the walls of the syringe. Each collision exerts a small force, and the total force per unit area is the gas pressure.
(a)(ii) The average speed of the particles increases.
Heating the gas transfers thermal energy to the particles, increasing their kinetic energy and causing them to move faster on average.
(a)(iii) The particles move faster, so collisions with the walls occur more frequently and with greater force, increasing the pressure.
At constant volume, the particles have less space to move, so the increased speed leads to a higher rate of collisions and a greater force per collision, resulting in higher pressure.
(b)(i) Solid
Sound travels fastest in solids because particles are closely packed together, allowing vibrations to be transferred quickly from particle to particle.
(b)(ii) 20,000 Hz (20 kHz)
Ultrasound is defined as sound waves with frequencies higher than the upper limit of human hearing, which is 20,000 Hz.
(b)(iii)
Step 1: Total distance travelled = speed × time = 1500 × \( 8.0 \times 10^{-5} \) = 0.12 m
Step 2: Depth = total distance ÷ 2 = 0.12 ÷ 2 = 0.060 m
Question
The activity of a sample of polonium-210 is measured as 680 counts per minute.
Calculate the time taken, in days, for the activity to decrease to 85 counts per minute.
Calculate the volume occupied by \(235\,\text{g}\) of solid polonium.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654, 2025–2027 syllabus):
• Topic P5.2.1 — Detection of radioactivity (Part (a))
• Topic P2.1.2 — Particle model (Part (b)(i))
• Topic P1.4 — Density (Part (b)(ii))
▶️ Answer/Explanation
(a)(i) Alpha particle
The mass number decreases by 4 (\(210 \rightarrow 206\)) and the atomic/proton number decreases by 2 (\(84 \rightarrow 82\)).
This change is characteristic of the emission of an alpha particle (\(^4_2He\)).
(a)(ii) 420 days
The activity falls from 680 to 85 counts per minute: \(\dfrac{680}{85} = 8 = 2^3\), so 3 half-lives have passed.
Time taken \(= 3 \times 140 = 420\) days.
(b)(i) Atoms vibrate in a fixed, regular arrangement
Both samples contain the same number of atoms, since they have the same mass.
In the solid, atoms vibrate about fixed positions in a regular, closely-packed arrangement.
In the liquid, atoms are free to move and are arranged randomly/irregularly, with more space between them, so the liquid takes up a larger volume for the same mass.
(b)(ii) \(25\,\text{cm}^3\)
Volume is calculated using \(V = \dfrac{m}{\rho}\).
\(V = \dfrac{235}{9.4} = 25\,\text{cm}^3\).