Verdict on the October/November 2025 Paper 42

The Cambridge IGCSE Physics Paper 42 (Extended Theory) represented a well-calibrated, highly balanced exam paper, rated at a 3.5 out of 5 in terms of difficulty. While it presented classic calculations, it also heavily penalized candidates who lacked conceptual precision, particularly in Lenz's law, wave refraction drawings, and centripetal force applications.

Where the Marks Were Won and Lost

  • Core Calculations: Candidates secured straightforward marks in Q1(b)(ii) for momentum calculation, Q2(a)(i) for Newton's second law, and Q7(b)(iii) for combined parallel resistance. These are standard formulaic calculations that require consistent unit usage.
  • Thermal Energy & Kinetic Model: High performance was observed on the calculation of gas volume using Boyle's Law \( p_1 V_1 = p_2 V_2 \) in Q4. However, describing evaporation in terms of the kinetic model in Q5 saw marks lost due to a lack of precise vocabulary; candidates must specify that it is the most energetic particles escaping from the surface of the liquid.
  • Electromagnetism and Wave Drawings: Major mark drops occurred in Q6(a)(i) with wave refraction drawings in shallower water, where candidates drew incorrect spacings (wavelengths) or missed connecting wavefronts continuously across boundaries. Similarly, Fleming's Left-Hand Rule in Q9(a) and Lenz's Law in Q8(b) proved to be powerful discriminators.

Examiner Trap Warning

One of the most notable traps occurred in Q3(b) where candidates had to calculate the input power of solar panels from an output of 3.5 kW and efficiency of 16%. A large portion of candidates multiplied \( 3.5 \times 0.16 \) instead of dividing, resulting in an unrealistically low input power. Additionally, converting time units (such as 2.0 hours to 7200 seconds in Q3(e) or keeping hours for kWh calculation in Q7(b)(ii)) remained a chronic source of errors.

Preparation Strategy & Predictions

To master upcoming series, students must move beyond mere formula memorization and practice qualitative descriptions of physics phenomena. Our trend analysis predicts that topics entirely absent from this series—specifically, Sound waves (longitudinal properties and echo experiments), the Electromagnetic Spectrum (applications and safety), and Specific Heat Capacity calculations—are highly overdue and likely to be central pillars of the next examination paper.