1. Unit G485: Fields, Particles and Frontiers of Physics Revision

2. Unit Structure 1.Electric and magnetic fields 2.Capacitors and exponential decay 3.Nuclear physics 4.Medical imaging 5.Modelling the universe

3. Describe the magnetic field patterns of a long straight current-carrying conductor and a long solenoid Electric and Magnetic Fields

4. Define Magnetic Flux Density A measure of the strength of a magnetic field at a given point, expressed by the force per unit length on a conductor carrying unit current at that point. B = F / IL

5. Electric and Magnetic Fields Define Magnetic flux Magnetic flux = magnetic flux density x cross-sectional area perpendicular to field direction (B x A normal to B).

6. Electric and Magnetic Fields Define Magnetic flux

7. Electric and Magnetic Fields Define Magnetic flux linkage Magnetic flux linkage =NBA

8. Electric and Magnetic Fields State and use Fleming’s left-hand rule. If the first two fingers and thumb of the left hands are placed at right angles then the first finger is in the direction of the field, the second in the direction of the current and the thumb in the direction of motion.

9. Electric and Magnetic Fields State and use Faradays Law of electromagnetic induction Induced e.m.f is proportional to the rate of change of (magnetic) flux

10. Electric and Magnetic Fields

11. Describe Lenz’s Law The direction of the emf induced in a conductor is such as to oppose the change producing it.

12. Electric and Magnetic Fields Applying Lenz’s Law Which magnet will reach the bottom of the tube first ? The non magnetised. The magnetised steel will induce an emf in the copper which in turn will create eddy currents in the copper. These eddy currents will produce a magnetic field which will oppose the change producing them – they will slow down the steel.

13. Electric and Magnetic Fields State and use Faradays Law of electromagnetic induction - The Graph Question Graphical analysis often involves a graph of flux linkage. Note that to work out the total flux linkage you will have to multiply by the number of turns. To work out the rate of change you will have to work out the gradient.

14. Electric and Magnetic Fields State and use Faradays Law of electromagnetic induction - The ac Generator Question

15. Electric and Magnetic Fields Describe the function of a simple ac generator An electric generator converts mechanical energy in the form of the rotation energy of a coil of wire into electrical energy.

16. Electric and Magnetic Fields State and use Faradays Law of electromagnetic induction – The Aircraft Question Emf generated = Blv ( where v is the velocity NOT voltage)

17. Electric and Magnetic Fields Analyse the circular orbits of charged particles in magnetic fields You will have to equate BQv and mv 2 /r The particle does not speed up because the force is perpendicular to its velocity so no work is done in the direction of its velocity.

18. Electric and Magnetic Fields

19. Describe how electric field lines represent an electric field The direction of the electric field is defined as the direction in which a positive charge would move if it were free to do so. So the lines of force can be drawn with arrows that go from positive to negative.

20. Electric and Magnetic Fields State what is meant by an electric field An electric field is a region of space where a stationary charge experiences a force due to its charge.

21. Electric and Magnetic Fields How do we work out the force between two charges ? Similar to Newton’s Law of Gravitation Both fields are radial and 1/r 2 But electric can be repulsive as well as attractive.

22. Electric and Magnetic Fields Define Electric Field Strength Electric field strength at a point in space is the force per unit positive charge.

23. Electric and Magnetic Fields Electric Field Strength - Numerically Units Vm -1 or NC -1

24. Electric and Magnetic Fields Explain the effect of a uniform electric field on the motion of a charged particle If E is uniform, then the acceleration of the charged particle is constant. If the particle has a positive charge, then its acceleration is in the direction of the electric field. If the particle has negative charge, then its acceleration is in the direction opposite the electric field.

25. Electric and Magnetic Fields Explain the effect of a uniform electric field on the motion of a charged particle You may have to use the equations of motion once you have worked out an acceleration ( F = eE and F = ma ) Remember there is no horizontal acceleration.

26. Electric and Magnetic Fields Explain the effect of a uniform electric field on the motion of a charged particle- The Transfer Equation The most forgotten equation ! eV = ½ m v 2

27. Electric and Magnetic Fields Explain the use of deflection of charged particles in the magnetic and electric fields of a mass spectrometer

28. Electric and Magnetic Fields Explain the use of deflection of charged particles in the magnetic and electric fields of a mass spectrometer The question is nearly always about the radius !

29. Electric and Magnetic Fields Describe the function of a simple transformer. A simple transformer is two coil of insulated wire wound on to a laminated soft iron core. And alternating e.m.f is applied across the primary coil. The current produced creates an alternating magnetic field which links the secondary coil and an e.m.f is induced in the secondary

30. Electric and Magnetic Fields Describe the function of a simple transformer. Numerically

31. Electric and Magnetic Fields Define The Tesla This is the magnetic flux density if a wire of length 1m carrying a current of 1 A has a force of 1 N exerted on it in a direction perpendicular to both the flux and the current.

32. Electric and Magnetic Fields Define The Weber The Weber is the magnetic flux which, linking a circuit of one turn, would produce in it an electromotive force of 1 volt if it were reduced to zero at a uniform rate in 1 second. (From Faradays Law) One Weber is equal to one Tesla metre²