# Magnetism, Nuclei & Options

## Contents

# PH5.1 CAPACITANCE

Content

- The parallel plate capacitor.
- Concept of capacitance.
- Factors affecting capacitance.
- Energy stored in a capacitor.
- Capacitors in series and parallel.
- Capacitor discharge.

AMPLIFICATION OF CONTENT Candidates should be able to:

5.1 (a) understand that a simple parallel plate capacitor consists of a pair of equal parallel metal plates separated by vacuum or air,

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

5.1 (c) define capacitance as C=Q/V,

5.1 (d) use C=εoA/d for a parallel plate capacitor, with no dielectric,

5.1 (e) know that a dielectric increases the capacitance of a vacuum-spaced capacitor;

5.1 (f) recall that the E field within a parallel plate capacitor is uniform and of value V/d,

5.1 (g) use the equation U=1/2QV for the energy stored in a capacitor,

5.1 (h) use formulae for capacitors in series and in parallel,

5.1 (i) understand the process by which a capacitor discharges through a resistor,

5.1 (j) use the equation Q=Q0e−t/RC where RC is the time constant.

# PH5.2 B-FIELDS

Content

- Concept of magnetic fields (B-fields).
- Force on a current-carrying conductor.
- Force on a moving charge.
- Magnetic fields due to currents.
- Effect of a ferrous core.
- Force between current – carrying conductors.
- Definition of the ampere.
- Measurement of magnetic field strength B.
- Deflection of beams of charged particles in electric and magnetic fields.

AMPLIFICATION OF CONTENT Candidates should be able to:

5.2 (a) predict the direction of the force on a current-carrying conductor in a magnetic field,

5.2 (b) define magnetic field B by considering the force on a currentcarrying conductor in a magnetic field; recall and use F = BIl sin θ ,

5.2 (c) use F = Bqv sinθ for a moving charge in a magnetic field;

5.2 (e) understand the processes involved in the production of a Hall voltage and understand that VH ∝ B for constant I.

5.2 (f) describe how to investigate steady magnetic fields with a Hall probe,

5.2 (g) sketch the magnetic fields due to a current in (i) a long straight wire, (ii) a long solenoid,

5.2 (h) use the equations B=μ0I/2πa and B=μ0nI for the field strengths due to a long straight wire and in a long solenoid,

5.2 (i) know that adding an iron core increases the field strength in a solenoid,

5.2 (j) explain why current-carrying conductors exert a force on each other and predict the directions of the forces,

5.2 (k) understand how the equation for the force between two currents in straight wires leads to the definition of the ampere,

5.2 (m) describe quantitatively how ion beams, i.e. charged particles, are deflected in uniform electric and magnetic fields,

5.2 (o) apply knowledge of the motion of charged particles in magnetic and electric fields to linear accelerators, cyclotrons and synchrotrons.

# PH5.3 ELECTROMAGNETIC INDUCTION

Content

- Magnetic flux.
- Laws of electromagnetic induction.
- Calculation of induced emf.
- Self induction.

AMPLIFICATION OF CONTENT Candidates should be able to:

5.3 (a) recall and define magnetic flux as Φ = ABcosθ and flux linkage = NΦ;

5.3 (b) recall the laws of Faraday and Lenz,

5.3 (c) recall and use e.m.f. = – rate of change of flux linkage and use this relationship to derive an equation for the e.m.f. induced in a linear conductor moving at right angles to a uniform magnetic field,

5.3 (d) relate qualitatively the instantaneous e.m.f. induced in a coil rotating at right angles to a magnetic field to the position of the coil, flux density, coil area and angular velocity;

5.3 (e) understand and use the terms frequency, period, peak value and rootmean- square value when applied to alternating voltages and currents,

5.3 (f) understand that the r.m.s. value is related to the energy dissipated per cycle, and use the relationships Vrms=V0/√2 and Irms=I0/√2

5.3 (g) recall that the mean power dissipated in a resistor is given by=VI=V^2/R=I^2R , where V and I are the r.m.s. values; (i) describe the use of a cathode ray oscilloscope to measure: (ii) a.c. and d.c. voltages and currents, (iii) frequencies.

# PH5.4 RADIOACTIVITY AND RADIOISOTOPES

Content

- Radioactive decay.
- Half-life.
- Applications of radioactivity.
- Hazards and safety precautions.

AMPLIFICATION OF CONTENT Candidates should be able to:

5.4 (a) recall the spontaneous nature of nuclear decay; describe the nature of α, β and γ radiation, and use equations to represent the nuclear transformations using the X,Z & A notation,

5.4 (b) describe methods used to distinguish between α, β and γ radiation and explain the connections between the nature, penetration and range for ionising particles,

5.4 (c) account for the existence of background radiation and make allowance for this in experimental measurements,

5.4 (d) explain what is meant by half-life T1/2,

5.4 (e) define activity A and the becquerel,

5.4 (f) define decay constant ( λ ) and recall and use the equation A = –λ N.

5.4 (g) recall and use the exponential law of decay in graphical and algebraic form, N=N0E-λt or (N=N0/2^x) and A=A0e-λt or (A=A0/2x) where x is the number of half-lives elapsed – not necessarily an integer,

5.4 (h) derive and recall that λ=loge2/T1/2,

5.4 (i) describe briefly the use of radioisotopes (any two applications),

5.4 (j) show an awareness of the biological hazards of ionising radiation e.g. whether exposed to external radiation or when radioactive materials are absorbed (ingestion and/or inhalation).

# PH5.5 NUCLEAR ENERGY

Content

- Binding Energy.
- Fission and Fusion.
- Nuclear Reactors.

AMPLIFICATION OF CONTENT Candidates should be able to:

5.5 (a) appreciate the association between mass and energy and recall that E = mc2 ,

5.5 (b) calculate the binding energy for a nucleus and hence the binding energy per nucleon, making use, where necessary, of the unified atomic mass unit (u) and the electron-volt (eV), 5.5 (c) apply the conservation of mass/energy to particle interactions – e.g. fission, fusion and neutrino detection interactions;

5.5 (d) describe the relevance of binding energy per nucleon to nuclear fission and fusion,

5.5 (e) explain how neutron emission gives the possibility of a chain reaction,

5.5 (f) understand and describe induced fission by thermal neutrons and the roles of moderator, control rods and coolants in thermal reactors,

5.5 (g) understand and recall the factors influencing choice of materials for moderator, control rods and coolant,

5.5 (h) discuss the environmental problems posed by the disposal of the waste products of nuclear reactors.