Summary
Highlights
Pat Doyle welcomes students to the Leaving Certificate Physics masterclass. He emphasizes that despite feeling rushed, students have approximately four months until the physics exam, which is ample time for significant work, including revision and finishing any remaining topics. The focus is on planning study effectively.
Section A of the exam deals exclusively with 24 mandatory experiments. Pat highlights that with 90+ past paper questions available, all experiments have likely been asked multiple times, making past papers vital for preparation. The only experiment never featured is the refractive index of a liquid using real and apparent depth. He stresses that learning procedures by heart is a waste of time; instead, focus on what data is measured and how it's measured, using examples like measuring 'small G' or specific heat capacity. Always refer to past paper questions and their solutions or marking schemes for guidance.
A common challenging aspect in Section A is drawing a graph, finding its slope, and then relating that slope back to an equation. Pat provides an example of a stretched string experiment where frequency is inversely proportional to length. Students must calculate the reciprocal of length, plot frequency against 1/length, find the slope, and then substitute it into the governing equation (F = 1/2L * sqrt(T/μ)) to find 'μ' (mass per unit length). He notes this method, last seen in 2016, is a common trick. Another example discussed is the resistivity of a wire, where plotting resistance against length and finding the slope helps calculate resistivity.
Pat explains the principle of taking large measurements to improve accuracy. Using an example of measuring a marker with a faulty ruler, he demonstrates that a fixed error (e.g., 1mm) results in a smaller percentage error when the overall measurement is larger. This means always opting for larger angles, longer lengths, or larger masses in experiments to minimize percentage errors. While students won't be asked to justify this, understanding the logic helps in applying the principle.
Pat outlines six key derivations students must know: the equations of motion, angular speed in circular motion (ω = v/R), Kepler's Third Law (T² ∝ R³), the diffraction grating equation (nλ = dsinθ), combining resistors in series and parallel, and the force on a charge in a magnetic field (F = QvB). He also adds Newton's Second Law (F = ma) as an unlisted but frequently tested derivation. He stresses the importance of learning these, as they often carry 12-15 marks, significantly impacting the overall grade. He demonstrates the derivation of T² ∝ R³ as an example, highlighting its weight in marks and its likelihood of appearing.
Pat advises a time management strategy of allocating 20 minutes per question for both Section A and Section B, even though Section B questions carry more marks. The first hour of the exam should be dedicated to reading, choosing three questions from Section A, and completing them. The remaining two hours are for Section B, where students must read and wisely choose five out of nine questions. He warns against doing extra questions if time remains, as marks are only awarded for the best five, and additional questions usually yield lower scores. Instead, use extra time to review existing answers for small errors like missing units or incorrect calculations.
He discusses a recurring nuclear fusion question from 2006 and 2012, involving the calculation of energy released (E=mc²). The challenge in 2012 was that the masses of the isotopes were not provided in the question itself but had to be found in the math tables (page 83 for isotopes, and pages 46-47 for conversion from 'u' to 'kg' and the mass of a neutron). He emphasizes becoming proficient in navigating the math tables to find necessary constants and data, as these questions become impossible otherwise. This particular fusion question is suggested as a valuable one to review given its absence for a while.