Exam techniques

• Describe and explain the motion of an object:

  • If velocity time graph is a straight line through the origin then acceleration is constant
  • This means there will be a constant force acting on the object —> F =ma
• Projectile motion:

  • Always have no acceleration in the horizontal direction and velocity is constant
  • Even if the acceleration in vertical direction is 0 there will always be a component of horizontal acceleration
  • Gravity is only force acting downward on projectile
• Archimedes principle:

  • If there is an object that is submerged the upthrust acting on the object is equal to the weight of the fluid that has been displaced
  • U = mg
• Springs in series:

  • 1/KT = 1/ K1 + 1/K2
• Springs in parallel:

  • Kt = K1 + K2
• • In a stress agains strain graph the area under the graph = the work done per unit volume
• The area of a force against time graph is the impulse

  • Impulse = change in momentum
• Kirchoff’s 1st law is the conservation of charge
• kirchoff’s 2nd law is the conservation of energy
• Microwaves are around a few cm in wavelength
• X-rays are around 10^-10 to 10^-12m
• visible light is around 400-700nm
• Shorter waves are blue, longer waves are red
• Finding the critical angle between 2 boundaries when one of the boundaries is not air:

  Sin C = n2 / n1
• Number of particles = mass / molar mass x Avogadro’s constant
• Assumptions of kinetic theory:

  • Large number of molecules in a random, rapid motion
  • Particles occupy negligible volume compared to the volume of gas
  • All collisions are perfectly elastic and the time of collisions is negligible compared to the time between collisions
  • negligible forces between particles except during collisions
• Internal energy —> the sum of all the randomly distributed kinetic and potential energies of all the atoms of a substance
• Absolute zero is a temperature at which the substance in a state of minimum internal energy
• At absolute zero internal energy is not zero as the molecules still have some potential energy
• For simple harmonic motion to occur:

  • acceleration must be proportional to displacement (negative) —. graph will be a straight line through the origin
  • Acceleration needs to be directed towards the equilibrium position
• Displacement equations for SHM:

  • x = Acos(wt)
  • x = Asin(wt)
  • All in radians
• • If the natural frequency matches the driving frequency resonance occurs
  • the amplitude reaches a maximum and maximum energy is transferred
• • In SHM, the time period is independent of the amplitude
  • Time period is constant even if system is damped
• Time constant —>time taken for the pd across the capacitor to fall to around 37% of its initial value during discharging
• Half-life of a capacitor:

  T= ln(2) x CR
• before being charged the capacitor has pd of 0 so pd across resistor os equal to the EMF
• Geostationary satellites have a period of 1 day
• Big Bang theory timeline;

  • Time and space created
  • At 10^-35sec the universe expands rapidly in a period of inflation
  • At 10^-6sec the first fundamental particles gain mass
  • At 10^-3 second quarks bind to form hadrons (protons and neutrons)
  • As the universe is expanding it is cooling
  • At 380000 years the universe cools enough for atoms to form
  • The nuclei capture electrons. EM radiation from this stage is now detected as the Cosmic Microwave Background Radiation