OCR A Level Physics A Module 6: Particles and Medical Physics Exam Questions

About OCR A Level Physics A Module 6: Particles and Medical Physics

Module 6 of OCR A Level Physics A, Particles and Medical Physics, covers fields, nuclear and particle physics and the physics behind medical imaging. It includes capacitors and exponential decay, electric fields and potential, magnetic fields, charged particle motion and electromagnetic induction, the nucleus, fundamental particles, radioactivity, binding energy, fission and fusion, and medical imaging with X-rays, CAT scans, PET scans, gamma cameras and ultrasound. It builds on circuits from Module 4 and fields from Module 5. Examiners commonly test capacitor discharge, charged particles in fields, Faraday's law, decay calculations and the attenuation of X-rays and ultrasound.

What you need to know

• 6.1 Capacitance C = Q / V, capacitors in series and parallel, energy stored W = 1/2 QV, and charging and discharging with time constant CR and exponential equations.
• 6.2 Coulomb's law, electric field strength E = V / d for uniform fields, electric potential and energy, and the motion of charged particles in uniform fields.
• 6.3 Magnetic flux density, F = BIL sin(theta) and F = BQv, charged particles in magnetic fields including the velocity selector, Faraday's and Lenz's laws, generators and transformers.
• 6.4 Alpha scattering, nuclear radius, the strong nuclear force, hadrons, leptons and quarks, beta decay in terms of quarks, half-life and A = lambda N, mass defect, binding energy, fission and fusion.
• 6.5 X-ray production and attenuation I = I0 e^(-mu x), contrast media, CAT scans, medical tracers, gamma cameras, PET scans, ultrasound, acoustic impedance Z = rho c and Doppler imaging.

Common mistakes in Module 6: Particles and Medical Physics

• Saying a capacitor stores charge in its dielectric. Equal and opposite charges build up on the plates; the energy is stored in the electric field between them.
• Using the left-hand rule with electron flow without reversing direction. Fleming's left-hand rule uses conventional current, so reverse it for moving electrons.
• Forgetting the coupling gel's role in ultrasound. Gel has similar acoustic impedance to skin, preventing large reflection at the air-skin boundary.
• Confusing decay constant and half-life. They are linked by lambda t1/2 = ln 2; a larger decay constant means a shorter half-life.
• Describing PET as detecting positrons directly. Positrons annihilate with electrons, producing two gamma photons travelling in opposite directions, which are detected.

Try three Module 6: Particles and Medical Physics exam-style questions