Explain how the analysis of quantitative observations contributed to the development of the concept that certain matter and energy are quantised. (9 marks)
--- 18 WORK AREA LINES (style=lined) ---
Experiments such as Millikan’s oil drop experiment and others testing the photoelectric effect have demonstrated that certain quantities of matter and energy are quantised which means they are multiples of some fundamental value.
Millikan’s Oil Drop Experiment
→ Millikan’s oil drop experiment was able to show that charge is quantised.
→ Millikan levitated oil drops in an electric field by balancing the electric and gravitational forces on them. This allowed him to find the electric force acting on each oil drop, and using the mass of the oil drop he found its charge.
→ Analysing his results, he found that the charge on every oil drop was an integer multiple of `1.602 xx10^(-19) C`. This was determined to be the fundamental charge on an electron.
→ Further, with Thompson’s later discovery of the charge to mass ratio of an electron, its mass could be determined.
Photoelectric Effect
→ Photoelectric effect experiments showed the quantum properties of light which seemingly contradicted the view of light as a wave.
→ It was found that there was a minimum frequency (energy) of light that would cause photoemission when it was incident upon a metal plate, and no photoemission occurred with light lower than this frequency, regardless of intensity.
→ As one photon would strike one electron on the metal surface, the electron would receive a discrete amount of energy from that photon determined by its frequency `E=hf`. If a photon didn’t have enough energy, an electron couldn’t be removed.
→ This experimental evidence changed the conceptual understanding of energy within physics and provided a basis for the quantisation of the energy of light.
Other quantitative experiments that could be explored include:
→ Bohr’s analysis of emission spectra to demonstrate the existence of quantised energy levels in atoms.
→ Cathode ray experiments showing the particle nature of electrons.
→ Blackbody radiation experiments.
Experiments such as Millikan’s oil drop experiment and others testing the photoelectric effect have demonstrated that certain quantities of matter and energy are quantised which means they are multiples of some fundamental value.
Millikan’s Oil Drop Experiment
→ Millikan’s oil drop experiment was able to show that charge is quantised.
→ Millikan levitated oil drops in an electric field by balancing the electric and gravitational forces on them. This allowed him to find the electric force acting on each oil drop, and using the mass of the oil drop he found its charge.
→ Analysing his results, he found that the charge on every oil drop was an integer multiple of `1.602 xx10^(-19) C`. This was determined to be the fundamental charge on an electron.
→ Further, with Thompson’s later discovery of the charge to mass ratio of an electron, its mass could be determined.
Photoelectric Effect
→ Photoelectric effect experiments showed the quantum properties of light which seemingly contradicted the view of light as a wave.
→ It was found that there was a minimum frequency (energy) of light that would cause photoemission when it was incident upon a metal plate, and no photoemission occurred with light lower than this frequency, regardless of intensity.
→ As one photon would strike one electron on the metal surface, the electron would receive a discrete amount of energy from that photon determined by its frequency `E=hf`. If a photon didn’t have enough energy, an electron couldn’t be removed.
→ This experimental evidence changed the conceptual understanding of energy within physics and provided a basis for the quantisation of the energy of light.
Other quantitative experiments that could be explored include:
→ Bohr’s analysis of emission spectra to demonstrate the existence of quantised energy levels in atoms.
→ Cathode ray experiments showing the particle nature of electrons.
→ Blackbody radiation experiments.