Molecular kinetic theory modelAQA A-Level Physics: Flashcards

Exam questions on Molecular kinetic theory model

1. A student places smoke particles in a small glass cell filled with air and observes them through a microscope, lit from the side. Each smoke particle is seen as a tiny bright speck that moves along an irregular, zigzag path.
   Explain how this observation provides evidence for the existence of atoms and molecules.2 marks
2. A fixed mass of air is sealed inside a syringe. The temperature of the air can be kept constant, and the syringe can also be heated while its plunger is held fixed in position.
   The experiments on the syringe lead to the gas laws. Explain the difference between the gas laws and the kinetic theory model of a gas.2 marks
3. An ideal gas is modelled as $N$ identical molecules, each of mass $m$, moving randomly in a cubic container of side $L$ and volume $V$. Collisions with the walls are perfectly elastic. In part (b), the container holds 2.0 × 10²² molecules of nitrogen, each of mass 4.65 × 10⁻²⁶ kg, in a volume of 1.0 × 10⁻³ m³ at a pressure of 1.00 × 10⁵ Pa.
   A molecule of velocity component $c_x$ in the $x$ direction collides with the wall perpendicular to $x$ and rebounds along the same line. Show that the average force exerted on this wall by this molecule is $mc_x^2/L$.3 marks