CIE iGCSE Co-Ordinated Science P2.2.2 Melting, boiling and evaporation Exam Style Questions Paper 4
Question
A mountaineer climbs a mountain.
(a) At the top of the mountain there is some ice that is melting in the sunshine.
(i) State the melting point of water.
▶️Answer/Explanation
Melting point of water: 0°C (273 K)
Key notes:
1. Defined at standard atmospheric pressure (1 atm/101.3 kPa)
2. Same as freezing point (phase change equilibrium)
3. Important reference point in temperature scales
4. Can vary slightly with impurities or pressure changes
(ii) Describe, in terms of molecular motion and arrangement, how liquid water is different from ice.
▶️Answer/Explanation
Molecular differences:
1. Motion:
– Ice: Molecules vibrate about fixed positions
– Water: Molecules can move/slide past each other
2. Arrangement:
– Ice: Regular hexagonal lattice (open structure)
– Water: Random arrangement with transient hydrogen bonds
3. Density: Ice less dense due to ordered structure (why ice floats)
(b) On the mountain, the mountaineer is exposed to ultraviolet radiation. Ultraviolet radiation is an electromagnetic wave.
On Fig. 9.1 write ultraviolet in the correct place in the incomplete electromagnetic spectrum.
▶️Answer/Explanation
Correct order:
X-rays | ultraviolet | visible light | radio waves
Key points:
1. UV has shorter wavelength than visible light (10-400 nm vs 400-700 nm)
2. Higher frequency than visible light (7.5×1014-3×1016 Hz)
3. More energetic than visible light (causes sunburn/DNA damage)
4. Natural source: Sun (blocked partially by ozone layer)
(c) The mountaineer observes lightning striking a nearby mountain.
(i) There is an electric field between the negative charge on a cloud and the positive charge on the mountain.
State what is meant by an electric field.
▶️Answer/Explanation
Electric field definition:
A region of space where a charged particle experiences an electric force
Characteristics:
1. Created by electric charges
2. Represented by field lines (direction shows force on +ve test charge)
3. Strength measured in V/m or N/C
4. Stronger near charges, weaker with distance
5. In lightning: ~3×106 V/m breakdown strength in air
(ii) The lightning occurs when the cloud loses some of its charge to the mountain. The lightning flash discharges 3.0 C in 0.00012 s. Calculate the current that passes.
▶️Answer/Explanation
Calculation:
I = Q/t = 3.0 C ÷ 0.00012 s = 25,000 A
Context:
1. Typical lightning current: 30,000-50,000 A
2. Extremely high current explains destructive power
3. Lasts only milliseconds but heats air to ~30,000°C
4. Comparison: Household circuit ~15 A, car battery ~500 A cranking