Page 23 - Spotlight A+ Physics Form 4.5

Form
5 Physics Chapter 7 Quantum Physics

Ideas that Sparked the Quantum Physics 4. The light energy produced able to reach
Theory unlimited high value due to the frequency of the
electrons has no limit.
1. In a hot object, electrons vibrate rapidly and 5. When the temperature of the black body
randomly in any direction and produce light. increases, the intensity of radiation also increase
2. The hotter the object, the higher the energy and will not become zero value.
of electron vibration. Thus, more light will be 6. However, the experimental results of black-
emitted. body radiation are inconsistent with classical
3. As stated in classical theory, the electron that physics theory.
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vibrates at the same frequency should have the 7. Several physicists that involve in the quantum
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same energy content. theory development are shown as the following.

Classical Theory

(a) Isaac Newton (1643-1727)
• Described light as a single stream of
particles or corpuscles in 1704. Isaac Newton
• Unsuccessful in explaining the https://bit.ly/37FU9KI
phenomenon of light refraction due
to failure in comparing the speed of
light in glass and air.

(b) Thomas Young (1773-1829)

• Conducted doubleslit experiment
on light in 1801 and showed that Thomas Young
light is a wave. https://bit.ly/3ozx6aH
• Unable to explain the radiation
spectrum produced by black bodies.

(c) John Dalton (1766-1844)
• Matter consists of basic particles
that cannot be further divided John Dalton
called atoms. https://bit.ly/35BN6zU
• Same elements have the same type
of atoms.
• Unable to explain the light
spectrum produced by atoms.

(d) J.J. Thomson (1856-1940)

• Discovered negatively charged
subatomic particles called electrons J.J. Thomson
in 1897. https://bit.ly/3kpyFW1
• Designed experiment to study the
CHAP behaviour of electrons.
7 • Unable to explain the line spectrum
of light produced by atoms.

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