Page 239 - Physics Form 5 KSSM_Neat

Activity 7.2 ISS ICS CHAPTER 7

Aim: To compare the concepts of continuous energy and discrete energy
Instructions: Quantum Physics
1. Carry out this activity in groups.
2. Gather information related to the concepts of continuous energy and discrete energy on the
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following aspects:
(a) the visible light spectrum
(b) the line spectrum of mercury lamps and other lamps
(c) differences between continuous energy and discrete energy
3. You can obtain information from websites or various reading sources.
4. Present your findings using a graphical map.

Quantum of energy is discrete energy packet and not a continuous energy. The energy
depends on the frequency of the waves. According to Max Planck and Albert Einstein's quantum
theory, light energy exists in the form of an energy packet known as a photon. Photons are light
energies transferred in quantum of energy. The photon energy is directly proportional to the
frequency of light waves. The higher the frequency of light waves, the higher the energy quantum
of a photon.
Info GALLERY
Light is a type of electromagnetic
wave. It also behaves as a particle.
Other types of waves in the
electromagnetic spectrum can also
behave as particles.

Example 1 LET’S ANSWER
LET’S ANSWER
Compare the energy of a 400 nm and a 750 nm light photons.
Solution

Step 1: Step 2: Step 3: Step 4: https://bit.
Identify the Identify the Identify the Solve the problem ly/34tx1NS
problem information given formula to be used numerically

1 Energy of a 400 nm photon 3 c = lf, then f = c
Energy of a 750 nm photon l
E = hf = hc
l
2 Planck's constant, h = 6.63 × 10 J s
–34
8
Speed of light in vacuum, c = 3.00 × 10 m s –1 4 E = 6.63 × 10 ( 3.00 × 10 –9)
8
–34
Wavelength, l = 400 × 10 m 1 400 × 10
–9
1
–19
Wavelength, l = 750 × 10 m = 4.97 × 10 J
–9
2 3.00 × 10 8
E = 6.63 × 10 ( –9)
–34
2 750 × 10
= 2.65 × 10 J
–19
The shorter the wavelength of light, the higher the photon energy.
LS 7.1.2 7.1.4 229