Physics 9 Lesson 56: The effects of light
1. Theoretical Summary
1.1. Heat effect of light
– Light hitting objects will heat them up. The light energy is then converted into heat energy. That is the heat’s use of light.
In the heat effect of light, dark colored objects absorb light energy more strongly than light colored objects.
- Application: Making salt, drying clothes, drying rice…
1.2. Biological effects of light
Light can cause certain changes in organisms. That is the biological effect of light.
In this effect, light energy is transformed into other forms of energy needed by the organism.
C4: Give an example of the effect of light on plants.
C5: What are the effects of light on humans and the environment?
Synthesize vitamin D to help develop the bone system (best before 9am and after 4pm),…
Ultraviolet rays (especially midday) can cause blindness, skin cancer, …
Disinfection in the air and in water.
1.3. Photoelectric effect of light
a) Solar battery:
A solar cell is an electrical source that can generate electricity when light shines on it.
Some solar powered tools:
Pocket machines, artificial satellites, airplanes, cars, children’s toys…
C7What conditions must be met for the battery to generate electricity? When the battery is working does it heat up? So is the battery working due to the thermal effect of light?
b) Photoelectric effect of light:
The photoelectric effect of light on a photovoltaic cell is the photoelectric effect.
Some applications of solar cells in life and engineering: airplanes, cars, phones, computers,…
Light has thermal, biological, and photoelectric effects. That proves light has energy.
In the above effects, the energy of light is converted into other forms of energy.
Solar energy is clean and inexhaustible energy, a source of energy in the future
Some applications: Salt production, electricity generation, agricultural drying …
Heat effect, e.g. heating an object
Biological effects, e.g. helping plants to photosynthesize
Photoelectric effect, electricity production
2. Illustrated exercise
Question 1: Why should we wear dark colored clothes in winter and light colored clothes in summer?
In winter, you should wear dark clothes because dark clothes absorb a lot of sunlight energy and warm the body.
In the summer, you should wear light-colored clothes so that it absorbs less energy of sunlight, reducing the heat when we go out in the sun.
Verse 2: What conditions must be met for a solar battery to generate electricity? When the battery is working, does it heat up? So, is the battery working due to the effect of light or not?
In order for a solar battery to generate electricity, light must shine on the battery. When the battery is working, it does not heat up, or does not heat up significantly. Therefore, the battery does not work due to the thermal effect of light.
To confirm this conclusion, we put the battery in a dim place and put our hand on the battery to make it hotter than when shining on it, but it still doesn’t work.
3.1. Essay exercises
Question 1: What effects will the light on the solar battery pack installed on a pocket computer cause?
Verse 2: In the sunbathing of the elderly and the sunbathing of children, what effects of sunlight have been used?
Question 3: What are the effects of sunlight on plants?
Question 4: Which of the following is a biological effect of light?
3.2. Multiple choice exercises
Question 1: Choose the wrong option
The demonstrations of the thermal effect of light are:
A. Drying clothes
B. Making salt
C. Warming in winter
D. Photosynthesis of plants
Verse 2: In the summer, when we go out on the street during the day, we should not wear dark clothes because the clothes are dark
A. Absorbs little light so it feels hot.
B. Absorbs a lot of light so it feels hot.
C. scatters a lot of light so it feels hot.
D. less light scattering so it feels cool.
Question 3: Light has a thermal effect when light energy is converted into
B. thermal energy
C. mechanical energy
D. chemical energy
Question 4: Which of the following is not caused by light?
A. Heat effect
B. Photoelectric effect
C. Word effect
D. Biological effects
Through this lesson, students will be familiar with the knowledge related to the effects of light along with related exercises at many levels from easy to difficult…, they need to understand:
What are the effects of grasping the light? Each effect is given an illustrative example.
Compare fossil energy sources, nuclear energy with sunlight energy according to the following criteria: potential, impact on the environment. From there, please suggest about the use of energy sources in the future?
What are the applications of using solar energy today in life and technology?