Are You Prepared for This IB Physics HL Question? 70% Got It Wrong

IB Physics Paper 2 Electric and magnetic fields, alpha particles, charged-particle motion, electric potential, force balance, velocity selectors, and electron trajectories explained. This May 2025 Time Zone 2 IB Physics Paper 2 question looks fairly straightforward at first. But according to the examiner's report, its final one-mark part proved surprisingly difficult. Only *30% of HL students and 15% of SL students* earned the mark for part (d). And what did the question ask them to do? Simply draw the path of an electron! In this video, we solve Question 3 from the May 2025 TZ2 Physics Paper 2, starting with an alpha particle accelerating between two oppositely charged plates and progressing to a region containing both electric and magnetic fields. We cover: Calculating electric field strength from potential difference and plate separation Using electric force and Newton's second law to find acceleration Applying SUVAT equations to charged-particle motion Converting centimetres to metres correctly Why you should retain unrounded values in subsequent calculations Calculating kinetic energy gained by an alpha particle in electronvolts (eV) Understanding electric and magnetic forces acting simultaneously Recognising that an undeflected particle experiences zero net force Applying \(qE=qvB\) to calculate magnetic field strength Understanding why an electron can follow the same straight-line trajectory as an alpha particle The crucial idea comes towards the end. When the electric and magnetic forces balance, the particle experiences no net force perpendicular to its motion. And because the particle's charge cancels from the force-balance equation, replacing the alpha particle with an electron travelling at the same velocity does not change the condition for an undeflected path. This is an excellent example of how IB Physics tests the connection between different concepts rather than simply asking students to substitute numbers into equations. --- *QUESTION — MAY 2025, TIME ZONE 2, PAPER 2, QUESTION 3* Two oppositely charged parallel plates are a distance 8.0 cm apart. The potential difference between the plates is 120 V. An alpha particle is placed on the positively charged plate and released from rest. Gravity is ignored. *(a)* Calculate the electric field between the plates. *[1]* *(b)* *(i)* Show that the acceleration of the alpha particle is about \(7 \times 10^{10}\ \text{m s}^{-2}\). *[2]* *(ii)* Calculate the time taken for the alpha particle to reach the negative plate. *[2]* *(iii)* State, in eV, the kinetic energy of the alpha particle when it arrives at the negative plate. *[1]* *(c)* A magnetic field directed into the plane of the page is now established between the plates. An alpha particle enters the region between the plates with a horizontal speed of \(5.0 \times 10^5\ \text{m s}^{-1}\). The particle is not deflected. Calculate the magnitude of the magnetic field. *[2]* *(d)* The alpha particle in (c) is replaced by an electron. The electron enters the region between the plates with the same velocity as the alpha particle. Draw, on the diagram, the path of the electron. *[1]* Refer to the video for the original diagrams. --- Preparing for IB Physics SL or HL? STUCK IN PHYSICS focuses on understanding the concepts, interpreting exam questions correctly, recognising common mistakes, and applying physics to challenging past-paper problems. More IB Physics Paper 1A and Paper 2 solutions coming soon. Only 30% of HL students solved this IB Physics Paper 2 question correctly. Learn the trick to mastering charged particle motion. This video breaks down a challenging problem from the May 2025 TZ2 exam paper. We explore the physics of an alpha particle accelerating between charged plates and analyze how it behaves when entering a region containing combined electric and magnetic fields. Many students struggle with the final part of this question, which requires a conceptual understanding of forces rather than just rote formula substitution. We cover the step-by-step logic needed to earn full marks, including calculating electric field strength, applying Newton's second law, and understanding why the charge cancels out in force-balance equations. By reviewing these official exam solutions, you will learn how to avoid common pitfalls when handling complex mechanics and field interactions under timed conditions. Subscribe for weekly IB Physics breakdowns, and comment below which topic you want to cover next. 0:00 Analyzing the Parallel Plate Problem 1:33 Calculating Acceleration and Kinematics 5:37 Navigating Magnetic Field Interactions 8:37 The Electron Deflection Trap #IBPhysics #IBDPPhysics #IBPhysicsHL #IBPhysicsSL #IBPhysicsPaper2 #ElectricFields #MagneticFields #PhysicsPastPapers