Physics

• What is the concept of wave-particle duality?

  Matter particles have a dual wave-particle nature.
• What does De Broglie's hypothesis state?

  Particles can be described as matter waves.
• What is Planck's constant used for?

  It relates the energy of a photon to its frequency.
• How did Special and General Relativity and the development of quantum mechanics change physics?

  They dramatically changed the understanding of physical laws.
• How does light behave like a wave?

  It exhibits diffraction, refraction, reflection, and interference.
• How does light behave like a particle?


  It shows characteristic emission/absorption spectra and the photoelectric effect.
• What is the experimental evidence for De Broglie's 'matter waves'?

  • Electrons are accelerated by an electric field in a vacuum.
  • They pass through a crystalline material (like graphite).
  • This acts as a diffraction grating, causing an interference pattern.
  • The interference pattern demonstrates wave-like behavior.
• How does an excited gas produce a discrete emission spectrum?


  Electrons in the gas are excited above their ground state by collisions, producing photons with element-specific frequencies.
• How does a cool gas result in a discrete absorption spectrum when white light passes through it?

  Only photons of specific frequencies are absorbed, creating gaps in the continuous spectrum.
• Why are photon emission and absorption spectra evidence of the particle-like behavior of light?


  They demonstrate the interaction of photons with matter, supporting the idea of light acting as particles.
• What are the physical processes in a fluorescent tube that lead to visible light production?

  1. High potential difference is applied across electrodes.
  2. Free electrons are accelerated and collide with gas atoms.
  3. Electrons excite gas atoms, producing UV photons.
  4. UV photons are absorbed by the coating's atoms, which then emit visible light.
• What are energy levels in atoms?

  Electrons in atoms exist in discrete, well-defined energy levels.
• What is required for an electron to transition between energy levels?


  It needs to give or take energy in quantized amounts corresponding to the difference in energy levels.
• What happens when an electron is de-excited to a lower energy level?

  It emits a photon corresponding to the energy difference between the levels.
• What is the ground state of an atom?

  It is when all electrons occupy their lowest possible energy levels.
• What are the key points of the photoelectric effect?

  • Low frequency photons do not emit photoelectrons.
  • High frequency photons can liberate photoelectrons with kinetic energy.
  • The maximum kinetic energy of emitted photoelectrons is given by \(E_k = hf - W\).
  • The work function is the minimum energy required to release an electron from the metal.
• Why do photoelectrons have a range of kinetic energies from \(0 < E_k \leq E_k(max)\)?

  Photoelectrons absorb photons with varying energies, leading to different kinetic energies upon escape.
• What conclusions can be drawn from experiments regarding photoelectrons and threshold frequency?

  • No photoelectrons are emitted if the radiation frequency is below the threshold frequency.
  • The emitted photoelectrons have a variety of kinetic energies.
  • The intensity of radiation affects the number of emitted photoelectrons but not their maximum kinetic energy.
• How does classical theory of light differ from quantum mechanical observations regarding photoelectrons?

  Classical theory suggests intensity affects kinetic energy, while quantum mechanics shows a 1:1 interaction between photons and electrons.
• What is the equation for photon energy?

  E = hf\
• What is the work function in the context of the photoelectric effect?

  It is the minimum energy required for an electron to escape the surface of a metal.
• How does the threshold frequency relate to the work function?

  The threshold frequency is the minimum frequency of light needed to overcome the work function.
• What is the mass of an object a measure of?

  The mass of an object is a measure of its inertia.
• What does inertia refer to in physics?

  Inertia is resistance to change in motion.
• What tendency do all objects have regarding their state of motion?

  All objects have a tendency to resist their change in state, be it rest or uniform motion.
• What is friction?

  Friction is a force that opposes motion.
• What are the two main types of friction?

  • Contact friction: Acts between solid surfaces and is proportional to the surface normal reaction.
  • Fluid friction (drag or fluid resistance): Increases with viscosity of fluid, speed of object, and area of object pushing through the fluid.
• What is lift in the context of forces acting on an object?

  Lift is an upward force acting on an object moving through a fluid.
• How does a wing generate lift?

  The wing pushes down on the air, changing its direction, causing an equal and opposite reaction force on the wing.
• What is the resultant force when it equals zero?

  The resultant force equals zero when all forces acting on an object are balanced.
• What happens to air resistance as the speed of an object increases?

  Air resistance increases with the speed of the object.
• How does air resistance affect the range and height of a projectile?

  Air resistance reduces the horizontal component of velocity, limiting the range, and reduces vertical components of velocity, limiting the maximum height reached.
• What is terminal velocity?

  Terminal velocity is reached when drag forces balance driving forces.
• How can the stopping distance of a car be calculated?

  Stopping distance is the sum of thinking and braking distances.
• What factors can affect thinking distance?

  Thinking distance can be affected by speed and awareness.
• What factors can affect braking distance?

  Braking distance can be affected by speed, road conditions (coefficient of friction), retarding frictional forces, and mass.
• How do cars reduce impact forces during a collision?

  Cars are designed to reduce impact forces through crumple zones, airbags, and seat belts, which increase impact times, hence reducing the force.
• What does the principle of conservation of momentum state?

  The total momentum of a system of interacting objects remains constant, provided no external resultant force acts upon the system.
• What happens to kinetic energy in an elastic collision?

  There is no loss of kinetic energy in an elastic collision.
• What characterizes an inelastic collision?

  An inelastic collision occurs when the colliding objects have less kinetic energy after the collision than before.