# HSC Physics Revision 2017

/The HSC Physics examination is on October 30. From now until this date I will list questions to help students revise for their Physics examination. This list will be updated during the next two months.

Students can increase their marks significantly during this period if they are positive, organised and have a plan. Remember that the HSC Physics examination is not "difficult Physics". What is required is a steady approach to study with adequate nutrition, sleep, exercise and recreation.

**Accelerating Reference Frame**A train moving in a straight line on horizontal ground is accelerating to the east. A ball is released from rest (relative to the floor of the train) from a height of 2.0 m. Sketch the path of the ball in the reference frame of the (i) train, if the train is moving to the east (ii) Earth, if the train is moving to the east (iii) train, if the train is moving to the west, and (iv) Earth, if the train is moving to the west.**AC Motor**An AC generator is reversed so that AC is now fed into the coil through the brushes that rub against the slip rings. Does the coil spin?**Photocells and Solar Cells**Describe the differences between a photocell and a solar cell.**Cloud Chamber**Describe how a cloud chamber detects the presence of radiation. Which radiation produces the (i) thickest tracks? (ii) thinnest tracks? (iii) straightest tracks? (iv) Can gamma rays be directly observed in a cloud chamber?**Earth Satellite**A satellite is in orbit above the Earth's equator. Determine the altitude of the satellite if it (i) appears stationary above the equator, (ii) appears to pass overhead (as seen by a person on the equator) from west to east every 8 hours, (iii) appears to pass overhead from east to west every 8 hours.**Magnetic Field of Two Currents**Two long straight parallel wires at a distance*d*apart carry currents of*I*and*4I*in opposite directions. Where is the resultant magnetic field strength zero?**Heinrich Hertz**Describe how Hertz discovered the photoelectric effect.**Strong Nuclear Force**Sketch graphs showing the force between two nucleons and the potential energy of two nucleons as a function of their distance apart.**Artificial Gravity**A space station far away from any planet or star has the shape of a torus of outer radius 500 m. It rotates about an axis through its centre and perpendicular to its plane at constant rate of 10 rev/min. An astronaut of mass 80 kg is standing on the inside of the outer surface of the space station (i) describe the force/s acting on the astronaut, (ii) determine the weight of the astronaut (iii) an apple is released from rest inside the spacestation at a distance of 1 m from the outer wall. Describe the subsequent motion of the apple.**EMF and Back EMF**What is the difference between an induced EMF (as in a generator) and a back EMF (as in a motor)?**CRO**Describe how an electron beam produces a two dimensional image on the screen of a cathode ray oscilloscope.**Electron in the Hydrogen Atom**According to quantum physics, how do we describe the electron in the hydrogen atom?**Maximum Range**A basketball is thrown at a speedan angle 𝜽 to the horizontal from of a height*U*above the ground. Show that the angle that gives the maximum range on the ground is given by*h***csc**^{2}𝜽_{max}**=****2(1**+/*gh**U*^{2}**)**.**Magnetic Force**Two electrons are moving at the same velocityrelative to the laboratory side by side in parallel paths a distance*v*apart in the laboratory reference frame. Determine the magnitude of the resultant force between the electrons in the (a) reference frame of the electrons, (b) laboratory reference frame.*d***Planck and Einstein**Outline the political views of Max Planck and Albert Einstein. How did this affect their scientific work?**Enrico Fermi**Assess the contribution of Enrico Fermi to Physics.**High Speed Electron**An electron is accelerated from rest through a potential difference of 100,000 V using a particle accelerator. Find the final speed of the electron.**Loudspeaker**Describe how a loudspeaker uses the motor effect to produce sound waves.**Blackbody Radiation Curve**Explain why the blackbody radiation curve has a peak at a certain wavelength. Does a photon of this wavelength have the greatest energy?**Linear Accelerator**Describe how a linear accelerator produces a high speed particle.**Projectile Practical**A marble is projected horizontally at a known constant speed from a spring gun at various heights above the floor and the horizontal range is measured in each case. (i) Plot this data so that a straight line graph is produced, (ii) how can the graph be used to determine g?**Step-Up Transformer**A step-up transformer is used to increase the voltage of an AC supply with respect to the ground. Explain how this reduces reduces the heat loss along the transmission line from the power station.**Phonons**A student in an answer to a question on the BCS theory mentions a "phonon". Outline what a phonon is.**Forces of Nature**Outline the force that holds together, giving the carrier particle in each case (i) the nucleons in an alpha particle, (ii) the quark combination that produces a proton**Michelson and Morley**Describe the result of the Michelson and Morley experiment.**Torque and Work**Describe the difference between torque and the work done by a force.**n-type Semiconductor**Is an n-type semiconductor negatively charged?**Binding Energy**The mass of the two protons, two neutrons and two electrons is greater than their combined mass when they form a helium atom. Describe why this is so.**Gravitational Potential Energy**When is the gravitational potential energy of two masses least? When they are close together or far apart? Explain.**Cathode Rays**Describe Thomson's experiment to measure the charge to mass ratio of cathode rays.**Bragg Diffraction**Using a labelled diagram, explain using wave concepts how constructive interference occurs when x-rays strike a solid object.**Line Spectrum**Explain how the presence of a line spectrum indicates the existence of energy levels in the hydrogen atom.**Orbital Decay**In an answer a student states that the speed of an orbiting satelite decreases when it is subjected to air drag. Is this correct?**Back EMF**Does the back emf eventually stop the coils of a DC motor from spinning? Explain.**Electromagnetic Waves**Describe how Heinrich Hertz experimentally produced radio waves and identified these as belonging to the same group as light waves.**Moderator**A neutron given off in a fission reaction has a kinetic energy of 6.0x10^{-13}J. This is reduced to 6.0x10^{-21}J by causing the neutron to make a series of collisions with carbon nuclei in the moderator. The fractional loss of kinetic energy of a neutron at each collision is 0.14. Find the number of collisions involved in this process. [122]**Polar Orbit**A satellite is placed in an orbit that passes over points near the north and south poles of the Earth. Does this satellite possess more energy than a similar satellite in orbit at the same altitude above the equator?**Power**Which combination has the higher power? A large resistance*R*connected to a battery or a smaller resistance*r*?**Carbon**Carbon has 4 electrons in its outer shell. (a) is the outer shell the same as the valence band? (b) is its valence band full? (b) is carbon a semiconductor?**Electron Wavelength**Compared to an electron in the ground state, the wavelength of an electron in the first excited state of the hydrogen atom is (A) 1/4, (B) 1/2, (c) the same, (D) twice as large (E) 4 times as large**Acceleration**A student doing a physics problem calculates the acceleration of an electron as 2.0x10^{14}ms^{-2}. Is this possible?**DC Motor**A DC motor has a split-ring commutator and the coils are in a radial magnetic field. An open switch is in the circuit. The switch is now closed. Sketch graphs showing (A) the current flowing in the coils in terms of time (B) the torque exerted by the magnetic field on the coil in terms of time.**Band Structure**A conductor and a semiconductor are at room temperature. Choose the correct statement.(A) the conduction band of the conductor is empty (B) the conduction band of the semiconductor is empty (C) the conduction band of a semiconductor is partially filled (D) the conduction band of a conductor is full (E) the valence band of a semiconductor is full**Neutron**A neutron (A) is not affected by a magnetic field (B) has no spin about its axis (C) has a magnetic moment causing it to align itself with a magnetic field (D) has zero magnetic moment since it has zero charge (E) is made of a proton and an electron.**Orbit**A satellite of total mass m moves at a constant speed v in a circular orbit around a planet. It suddenly fires a projectile of mass 0.5m at a speed of 0.5v in the opposite direction to its initial velocity. After it launches the projectile the satellite (A) continues in the same orbit with the same speed, (B) moves to a higher orbit (C) escapes from the planet, (D) moves to a lower orbit, (E) continues in the same orbit with a shorter period**Soft Iron Core**The role of the iron core in a transformer is to (A) reduce the eddy currents, (B) connect together the primary and secondary coils, (C) increase the magnetic flux passing through the coils, (D) carry all of the magnetic field of the primary coil through the secondary coil, (E) change the voltage of the primary coil.**Type 1 and 2 Superconductors**Superconducting magnets use (A) type 1 superconductors since B=0 inside them, (B) type 1 superconductors since B≠0 inside them, (C) type 2 superconductors since B≠0 up to a certain value, (D) type 2 superconductors since B=0 inside them, (E) both type 1 and type 2 superconductors.**Bohr's Postulate**In 1913 Niels Bohr proposed that mvr = n h/(2𝜋), where n is the principal quantum number, m is the mass of the electron, v is the speed of the electron and r is the radius of the stationary state. (A) the original Bohr theory is still used to explain the hydrogen atom, (B) Bohr's equation gives the magnitude of the electron angular momentum that agrees accurately with modern experiments, (C) Bohr's equation was replaced since quantum mechanics predicts that for each value of n there are n possible values of the orbital angular momentum, (D) the electron is now considered to have non-zero orbital angular momentum in its ground state, (E) the electron is now considered to have zero orbital angular momentum for every value of n.**Projectile1**A ball is thrown at 49m/s at 60° to the horizontal. Neglecting air resistance, the times after projection when the velocity vector makes an angle of 30° with the horizontal are (A)2.16s, 6.50s (B) 2.33s, 6.33s (C) 2.89s, 5.77s (D) 3.66s, 5s (E) 4.00s, 4.66s.**Projectile2**A ball is thrown at 49m/s at 60° to the horizontal. Neglecting air resistance, the times after projection when the speed of the ball is 35m/s are (A) 0.48s, 8.18s (B) 1.10s, 7.56s (C) 1.78s, 6.88s (D) 2.56s, 6.10s (E) 4.00s, 4.66s.**Air Resistance**The drag force acting due to air resistance on a projectile is proportional to the square of the speed of the projectile. A projectile is thrown vertically upwards at 49m/s. The maximum height reached is 60m. The projectile is now thrown at the same speed at an angle to the vertical. The maximum possible range of the projectile on the horizontal is (A) 30m (B) 60m (C) 94m (D) 120m (E) 180m**Speed**A projectile is thrown at 49m/s at 60° to the horizontal in the absence of air resistance. The gradient of the distance travelled-time graph for the projectile has a maximum value of (A) 98m/s, (B) 75m/s, (C) 49m/s, (D) 42m/s, (E) 24.5m/s.**Average Speed**Two identical projectiles, P and Q, are thrown on level ground at the same speed. P is thrown at 30° to the horizontal and Q is thrown at 60° to the horizontal. Neglecting air resistance, (A) the range of P is greater than Q, (B) the average speed of each projectile is the same during their flight, (C) the average speed of P is greater than the average speed of Q, (D) the average speed of P is less than the average speed of Q, (E) the average velocity of each object is the same during the flight.