Physics Unit 4 - Specification

4.1 - CAPACITANCE

(a) the idea that a simple parallel plate capacitor consists of a pair of equal parallel metal plates separated by a vacuum or air

(b) a capacitor storing energy by transferring charge from one plate to the other, so that the plates carry equal but opposite charges (the net charge being zero)

(c) the definition of capacitance as C = Q / V

(d) the use of C = ε_o A / d for a parallel plate capacitor, with no dielectric

(e) the idea that a dielectric increases the capacitance of a vacuum-spaced capacitor

(f) the E field within a parallel plate capacitor being uniform and the use of the equation E = V / d

(g) the equation U = ½QV for the energy stored in a capacitor

(h) the equations for capacitors in series and in parallel

(i) the process by which a capacitor charges and discharges through a resistor

(j) the equations: Q = Q_o (1- e^{- t / RC} ) and Q = Q_o e^{- t / RC} where RC is the time constant

4.2 - ELECTROSTATIC AND GRAVITATIONAL FIELDS OF FORCE

(a) the features of electric and gravitational fields as specified in the table below

(b) the idea that the gravitational field outside spherical bodies such as the Earth is essentially the same as if the whole mass were concentrated at the centre

(c) field lines (or lines of force) giving the direction of the field at a point, thus, for a positive point charge, the field lines are radially outward

(d) equipotential surfaces joining points of equal potential and are therefore spherical for a point charge

(e) how to calculate the net potential and resultant field strength for a number of point charges or point masses (f) the equation ΔU_P = mgΔh for distances over which the variation of g is negligible

4.3 - ORBITS AND THE WIDER UNIVERSE

(a) Kepler's three laws of planetary motion

(b) Newton's law of gravitation F = G M₁M₂ / r² in simple examples, including the motion of planets and satellites

(c) how to derive Kepler's 3rd law, for the case of a circular orbit from Newton's law of gravity and the formula for centripetal acceleration

(d) how to use data on orbital motion, such as period or orbital speed, to calculate the mass of the central object

(e) how the orbital speeds of objects in spiral galaxies implies the existence of dark matter

(f) how the recently discovered Higgs boson may be related to dark matter

(g) how to determine the position of the centre of mass of two spherically symmetric objects, given their masses and separation, and calculate their mutual orbital period in the case of circular orbits

(h) the Doppler relationship in the form Δλ / λ = v / c

(i) how to determine a star's radial velocity (i.e. the component of its velocity along the line joining it and an observer on the Earth) from data about the Doppler shift of spectral lines

(j) the use of data on the variation of the radial velocities of the bodies in a double system (for example, a star and orbiting exo-planet) and their orbital period to determine the masses of the bodies for the case of a circular orbit edge on as viewed from the Earth

(k) how the Hubble constant (H₀) relates galactic radial velocity (v) to distance (D) and it is defined by v = H_oD

(l) why 1 / H_o approximates the age of the universe

(m) how the equation ρ_c = 3H₀² / 8𝛑G for the critical density of a 'flat' universe can be derived very simply using conservation of energy

4.4 - MAGNETIC FIELDS

(a) how to determine the direction of the force on a current carrying conductor in a magnetic field

(b) how to calculate the magnetic field, B, by considering the force on a current-carrying conductor in a magnetic field i.e. understand how to use F = BIl sin Θ

(c) how to use F = B_q vsinΘ for a moving charge in a magnetic field

(d) the processes involved in the production of a Hall voltage and understand that V_H ∝ B for constant, I

(e) the shapes of the magnetic fields due to a current in a long straight wire and a long solenoid

(f) the equations B = μ₀I / 2𝛑a and B = μ₀ nI for the field strengths due to a long straight wire and in a long solenoid

(g) the fact that adding an iron core increases the field strength in a solenoid

(h) the idea that current carrying conductors exert a force on each other and to predict the directions of the forces

(i) quantitatively, how ion beams of charged particles, are deflected in uniform electric and magnetic fields

(j) the motion of charged particles in magnetic and electric fields in linear accelerators, cyclotrons and synchrotrons

4.5 - ELECTROMAGNETIC INDUCTION

(a) the definition of magnetic flux as Φ = ABcos Θ and flux linkage = NΦ

(b) the laws of Faraday and Lenz

(c) and how to apply the laws of Faraday and Lenz (i.e. emf = - rate of change of flux linkage)

(d) the idea that an emf is induced in a linear conductor moving at right angles to a uniform magnetic field

(e) qualitatively, how the instantaneous emf induced in a coil rotating at right angles to a magnetic field is related to the position of the coil, flux density, coil area and angular velocity

4.6 - MEDICAL PHYSICS

(a) the nature and properties of X-rays

(b) the production of X-ray spectra including methods of controlling the beam intensity and photon energy

(c) the use of high energy X-rays in the treatment of patients (therapy) and low energy X-rays in diagnosis

(d) the equation I = I₀ exp( μ−x ) for the attenuation of X-rays

(e) the use of X-rays in imaging soft tissue, and fluoroscopy to produce real time X-rays using image intensifiers

(f) techniques of radiography including using digital image receptors

(g) the use of a rotating beam X-ray computed tomography (CT) scanner

(h) the generation and detection of ultrasound using piezoelectric transducers

(i) scanning with ultrasound for diagnosis including A-scans and B-scans incorporating examples and applications

(j) the significance of acoustic impedance, defined by Z = cρ for the reflection and transmission of sound waves at tissue boundaries, including the need for a coupling medium

(k) the use of the Doppler equation Δf / f₀ = 2v / c to study blood flow using an ultrasound probe

(l) the principles of magnetic resonance with reference to precession nuclei, resonance and relaxation time, and to apply the equation f = 42.6 x 10⁶ B for the Lamor frequency

(m) the use of MRI in obtaining diagnostic information about internal structures

(n) the advantages and disadvantages of ultrasound imaging, X-ray imaging and MRI in examining internal structures

(o) the effects of α, β, and γ radiation on living matter

(o) the Gray (Gy) as the unit of absorbed dose and the Sievert (Sv) as the unit of equivalent dose and effective dose. Define absorbed dose as energy per kilogram

(p) the use of the equations

• equivalent dose = absorbed dose × (radiation) weighting factor H = DW_g

and

• effective dose = equivalent dose × tissue weighting factor E = HW_T

(q) the uses of radionuclides as tracers to image body parts with particular reference to technetium-99m (Tc-99m)

(r) the use of the gamma camera including the principles of the collimator, scintillation counter and photomultiplier / CCD

(s) positron emission tomography (PET) scanning and its use in detecting tumours