# HSC Physics Final Revision 2016

With the 2016 HSC Physics examination now two weeks away here are some more study notes to help you increase your mark.

1. Projectile Motion Graphs Sketch the x versus t, y versus t, vx versus t, vy versus t, and vy versus y graphs for a projectile thrown at an angle to the horizontal near the surface of the Earth in the absence of air resistance. Many students find difficulty drawing the last graph.
2. Loudspeaker Write a paragraph describing how a loudspeaker uses the motor effect in its operation. Try to include a labelled diagram in this type of question.
3. Television Write a paragraph outlining how the image is produced in a conventional CRT display. Include a labelled diagram.

4. Binding Energy This concept has appeared in several examination papers in the Quanta to Quarks section even though that it is not listed as a "dot point". Draw the binding energy curve and explain where the energy released by the U-235 nucleus when it is split by a slow neutron comes from.

5. Projectile Calculation A ball is projected at an angle of 35 degrees to the horizontal and it is to pass through a narrow window that is 50 m horizontally and 25 m vertically above the point of projection. At what speed must the ball be projected? Neglect air resistance. This is a band 6 question. [60.4 m/s]

6. Transformer Explain, using the laws of Physics, if a transformer can operate if the input current in the primary coil is DC.

7. Silicon and Germanium Describe why silicon is now preferred to germanium in semiconductor devices.

8. Form of Energy Released The energy released in the nuclear fission of a U-235 nucleus by a slow neutron is approximately 200 MeV. In what forms is this energy released?

9. Circular Motion Explain, using a labelled diagram, why an object moving in a circular path at a constant speed is accelerating.

10. Back EMF Describe the emf induced in the coils of a DC motor when they spin in a magnetic field. Back emf is not a force!

11. Thermionic Emission Outline why the cathode of a thermionic device is heated.

12. Intensity of Spectral Lines Outline how the problem of the relative intensity of the spectral lines in the Rutherford-Bohr model of the atom was explained.

13. Space Travel Alpha Centauri is 4.3 light years from the Earth. A spacecraft travels from the Earth to Alpha Centauri at a constant speed of 0.9c. Find the time taken for this journey, according to a) the Earth's reference frame and b) the reference frame of the spacecraft.

14. AC Motors Describe how an AC motor operates.

15. Resistance Describe the cause of the electrical resistance of a conductor.

16. Chadwick's Experiment Describe how Chadwick discovered the neutron.

17. Space Travel Barnard's Star is 6.0 light years from the Earth. A spacecraft travels from the Earth to Barnard's Star at a constant speed of 2.0x108 m/s. Determine the distance travelled by the spacecraft according to the crew of the spacecraft during the journey.

18. AC and DC Are the energy losses over transmission lines using AC less than those with DC?

19. Solar Cell In a solar cell does it matter which semiconductor, n or p, is exposed to the light?

20. Radioactive Decay What is the definition of half-life? The half-life of Co-60 is 5.27 years. What are some uses of this radioisotope?

21. Non-Inertial Frame of Reference A bus starts from rest and accelerates to the east. A person in the bus drops a ball. What is the path of the ball according to (i) a person at rest on the Earth, (ii) the person on the bus.

22. Maximum Torque and Maximum EMF In a DC motor, state the angle between the plane of the coil and the magnetic field when maximum torque acts on the coil. In an AC generator, state the angle between the plane of the coil and the magnetic field when maximum emf is induced.

23. Undoped (Intrinsic) Semiconductors The charge carriers in a pure semiconductor can be negative and or positive. Electrons can gain thermal energy and jump across the small energy gap between the valence and conduction bands. The electron in the conduction band can carry a current through the semiconductor when a voltage is applied to it. When an electron moves to the conduction band it leaves behind a positively charged hole in the valence band which acts as a charge carrier. An electron from a nearby site can transfer into the hole creating a new hole. The current direction in the valence band is the direction of hole movement.

24. Controlled and Uncontrolled Fission Describe the differences between a controlled and uncontrolled fission reaction. What happens to the reaction if on average less than one neutron released per fission causes further fission?

25. Parabolic Path Explain, using the projectile motion equations, why a projectile thrown horizontally in a uniform gravitational field moves in a parabolic path.

26. Torque on a Coil Carrying a Current in a Uniform Magnetic Field What is the resultant force acting on a rectangular coil supported by an axle when it carries a current in a uniform magnetic field? Why does the coil rotate?

27. Doped (Extrinsic) Semiconductors Adding impurities changes the band structure and resistance. Semiconductors doped with donor atoms are called n-type because the majority charge carriers are electrons. The extra electron has an energy level just below the conduction band and so only a small amount of energy is needed to allow it to enter the conduction band. Semiconductors doped with acceptor atoms are known as p-type. The acceptor atom has an energy level just above the valence band and electrons from the valence band can gain thermal energy allowing them to jump to the acceptor level creating a positively charged hole in the valence band.

28. Cyclotron Frequency Two ions of equal charge to mass ratio move perpendicular to a uniform magnetic field. The first ion has a speed v and the second ion has a speed 2v. Which ion has the greater frequency of revolution about the field lines?

29. Escape Speed Write down the definition of escape speed. Assume that the Earth is a non-rotating, non-moving uniform sphere. Does the escape speed at any point on the surface of the Earth depend on the angle at which the object is projected?

30. Direction of Induced Current in a Generator Imagine that seen from the side the coil of a generator is spinning clockwise in a uniform magnetic field acting to the right. At a certain instant the coil is horizontal. Determine the direction of the current in the left side of the coil at this instant. [into the page]

31. Highest Temperature Superconductor The highest recorded temperature at which superconductivity occurs is 203 K (-70 degrees C) in hydrogen sulfide.

32. Properties of Neutrons. Identify 3 properties of neutrons and describe how these have been used in nuclear physics experiments.

33. Orbital Period The acceleration due to gravity at the surface of a planet of radius R is g. In terms of these variables, determine the orbital period of a satellite moving at an altitude R.

34. Is the Back EMF in a DC Motor always in the Same Direction? No, it changes direction every half cycle but remember that the current in each side of the coil also changes direction each half revolution so that the back emf always opposes the current..hence its name.

35. Heinrich Hertz and Cathode rays The first attempts to observe the deflection of cathode rays in an electric field were made by Hertz. They were unsuccessful, and this negative result was interpreted as evidence against the proposition that cathode rays were particles. (J J Thomson repeated this experiment and found that cathode rays were deflected..Hertz had too high a pressure in his discharge tube).

36. Uranium-235 Uranium-235 makes up 0.72% (far too low a percentage to undergo a natural fission chain reaction) of all natural uranium and it is the only fissile isotope found in nature. It undergoes fission by a slow (thermal) neutron to produce two fragments of higher binding energy per nucleon (for example, Ba-141 Ba and Kr-92) and 3 neutrons. The Little Boy atomic bomb dropped on Hiroshima in 1945 consisted of two subcritical masses of U-235 fired together to produce an uncontrolled chain reaction. The critical mass for a sphere of U-235 is 56 kg.

37. Harder Projectile A stone is thrown at an angle of 50° degrees to the horizontal and has a range of 60m on level ground. If the stone is now thrown at the same speed at 25° degrees to the horizontal, determine the new range. Neglect air resistance. [46.7m]

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