G10 PHY OPENER TERM 3 2026 MS

PHYSICS GRADE 10

OPENER TERM 3 2026

MARKING SCHEME

1. (a) Kelvin (K) ✓1 (b) Candela (cd) ✓1 (c) Ampere (A) ✓1

2. Main scale reading = 2.40 cm ✓1 Vernier scale reading = 5 × 0.01 cm = 0.05 cm ✓1 Total reading = 2.40 + 0.05 = 2.45 cm ✓1

3. Radius, r = 7 cm = 0.07 m. Height, h = 10 cm = 0.1 m. Volume, V = πr²h = (22/7) × (0.07)² × 0.1 ✓1 V = 0.00154 m³ ✓1 Density, ρ = Mass / Volume ✓1 ρ = 12.32 kg / 0.00154 m³ ✓1 ρ = 8000 kg/m³ ✓1

4. (a) Optics ✓1 (b) Thermodynamics ✓1 (c) Mechanics ✓1

5. Force is a push or pull on an object. ✓1 SI unit: Newton (N) ✓1

6. Water has higher adhesive forces (attraction to glass molecules) than cohesive forces (attraction between water molecules) ✓1, causing it to cling to glass. Mercury has stronger cohesive forces than adhesive forces ✓1, so it forms spherical drops and doesn't wet glass. ✓1

7. Force, F = mg = 0.2 kg × 10 N/kg = 2.0 N ✓1 Extension, e = 4.0 cm = 0.04 m ✓1 F = ke => k = F/e = 2.0 / 0.04 ✓1 k = 50 N/m ✓1

8. Force exerted = Weight = mg = 120 × 10 = 1200 N ✓1 (a) Maximum pressure occurs at minimum area. Min Area = 3 m × 2 m = 6 m² ✓1 P_max = F / A_min = 1200 / 6 ✓1 P_max = 200 Pa (or N/m²) ✓1 (b) Minimum pressure occurs at maximum area. Max Area = 5 m × 3 m = 15 m² ✓1 P_min = F / A_max = 1200 / 15 = 80 Pa ✓1

9. Pressure in liquid, P_L = ρgh = 1000 × 10 × 15 ✓1 = 150,000 Pa ✓1 Total Pressure = P_L + Atmospheric Pressure ✓1 Total Pressure = 150,000 + 101,325 = 251,325 Pa ✓1 (Units must be given for full marks) ✓1

10. (a) Mercury is highly dense, allowing a shorter, practical tube length (~76cm compared to ~10m for water) ✓1. It is opaque/silver, making it easy to read. It does not wet glass. (Any two, 1 mk each) (b) P = ρgh ✓1 h = 68 cm = 0.68 m ✓1 P = 13600 × 10 × 0.68 = 92,480 Pa ✓1

11. (a) Bright specks of light (smoke particles) moving randomly / in a continuous zig-zag motion. ✓2 (b) The smoke particles are bombarded continuously and randomly ✓1 by unseen, fast-moving air molecules ✓1. The unequal collisions cause the random zig-zag motion. ✓1 (c) The speed of the random motion (kinetic energy) increases (they move faster and more vigorously). ✓1

12. (a) Sketch showing the strip bending downwards (iron on the inside of the curve, brass on the outside). ✓1 for curve, ✓1 for brass outside, ✓1 for correct labels. (b) Thermostats / Fire alarms / Bimetallic thermometers (Any 1 mk)

13. (i) Conduction: The vacuum between the double glass walls prevents conduction (since it requires a material medium). ✓2 (ii) Convection: The vacuum also prevents convection. Also, the stopper/cork prevents convection currents from escaping at the top. ✓2 (iii) Radiation: The silvered interior/inner walls reflect radiant heat back inside, minimizing radiation loss. ✓2