Here are some final study notes for the HSC Physics examination on Thursday 1st November 2018. This list will be updated during the time up to the exam.
- Weight and gravitational force are the same.
- Work done is the change in gravitational potential energy.
- Work done is the area under the gravitational force versus distance graph.
- Gravitational force is the negative gradient of the gravitational potential energy versus distance graph.
- "g-force" is not a force. The net force that accelerates an astronaut upwards is the force of the seat pushing upwards minus the weight of the astronaut pulling downwards. g-force is the ratio of the seat force to the weight force.
- A train is moving to the east and slowing down with deceleration g. A person in the train drops a ball. Relative to the person in the train the ball moves with a vertical acceleration component g and a horizontal acceleration component g and appears to fall forward in a straight line at 45° below the horizontal.
- The escape speed from a point in a gravitational field is the speed with which a mass is projected so that its total energy is zero.
- An object is said to be weightless when it is in a reference frame that is moving at the acceleration due to gravity.
- Time dilation is when the time interval measured on a moving clock is less than the time interval measured on a clock at rest.
Motors and Generators
- The torque on a coil carrying a current is maximum when it is parallel to the magnetic field.
- The torque acting on one side of a square coil carrying a current in a magnetic field is one half of the total torque acting on the coil.
- When a conductor moves relative to a uniform magnetic field an emf is induced in the conductor. If the emf allows a current to flow a force opposing the change is exerted by the magnetic field on the current.
- When a conductor moves relative to a uniform electric field no emf is induced in the conductor.
- In induction effects, the external magnetic field exerts a force on the induced current that opposes the change.
- The presence of the iron core in a transformer allows the primary coil to produce a stronger magnetic field than with an air core. The iron core carries the magnetic flux from the primary coil through the secondary coil.
From Ideas to Implementation
- The electric force acting on an electron in a uniform electric field is in the opposite direction to the field lines.
- The magnetic force acting on a moving charge is perpendicular to both the velocity vector and the magnetic field direction.
- For a constant intensity of light, the number of electrons released per second in the photoelectric effect decreases as the frequency increases.
- For a constant frequency of light, the number of electrons released per second increases as the intensity of the light increases.
- The Planck radiation curve has a peak since relatively few atoms in the wall of a hot object are vibrating at high frequencies (each sending out a high energy photon) and many are vibrating at lower frequencies (each sending out a low energy photon).
- In the photovoltaic effect (in a solar cell) an electron in the valence band of the p-type semiconductor absorbs a photon (whose energy is greater than the band gap) creating a hole in the valence band and an electron in the conduction band. An electric field exists across the p-n junction and this pulls electrons to the n side where they can flow out of the cell if it is connected to a load resistor.
Quanta to Quarks
- The scattering of a small number of alpha particles through a large angle by a thin gold foil is experimantal evidence for a small positively charged nucleus with most of the volume of the atom empty space.
- The line spectrum of hydrogen is evidence for quantised energy levels in the hydrogen atom.
- Chadwick collided neutrons with hydrogen and nitrogen atoms and measured the speed of each target atom after collision. The mass of the neutron was determined by applying the laws of conservation of momentum and kinetic energy to the elastic collisions.
- Binding energy is the energy released when protons and neutrons combine to form a nucleus. Energy is released in nuclear fission because the total binding energy after reaction is greater than the total binding energy before reaction.
- "mass and energy are both but different manifestations of the same thing", Einstein quote.
- The anti-neutrino and electron given off in beta decay of a neutron share the released energy and momentum. In this process a down quark in a neutron is converted to an up quark by the release of a W minus boson which decays into an electron and an anti-neutrino. This decay happens as the nucleus is unstable due to it having too many neutrons for the number of protons present.