PHYSICAL PHENOMENA IN THE SURROUNDING
Welcome to Unit Seven! In this unit, we will explore the fascinating physical phenomena that shape our everyday experiences, focusing on light, vision, and sound.
Learning Outcomes
At the end of this unit, you will be able to:
- List some sources of light.
- Describe reflection and refraction.
- Explain dispersion of light.
- Show colors formed on the other side of the prism.
- Determine the purpose of light.
- Classify materials as transparent, translucent, and opaque.
- Demonstrate how an image is formed.
- Define sound as a form of energy.
- Explain how sound is formed and demonstrate its formation.
- Identify material mediums for sound propagation.
- Prioritize sound propagation in solid, liquid, and gases.
- Explain the cause and list strategies for sound pollution.
- Identify hearing levels for different sounds.
- Define echo and demonstrate its application.
- Define the term heat and explain its transfer mechanism.
- Classify materials as good or poor conductors of heat (insulators).
- Define magnetism, perform simple experiments, and construct magnetic lines of force.
- Explain the use of magnets and list materials for constructing simple circuits.
- Construct a simple circuit.
Key Terms
Light: A form of energy that enables us to see objects.
Sources of Light: Objects that emit their own light.
Reflection of Light: The bouncing back of light when it hits a surface.
Refraction of Light: The bending of light as it passes from one medium to another.
Dispersion of Light: The splitting of white light into its constituent colors.
7.1 Phenomena of Light (Source & Properties)
Light
Light is a fundamental form of energy that enables us to perceive objects around us. We see objects when light, either directly from a source or reflected from an object, enters our eyes.
Sources of Light
An object that produces and emits its own light is called a source of light, also known as a A luminous object is any object that produces and emits its own light, such as the Sun, a light bulb, or a firefly.luminous object
Conversely, objects that do not emit light are known as A non-luminous object is an object that does not produce its own light but becomes visible when light from a source reflects off its surface and enters our eyes. Examples include the Moon, a chair, or a book.non-luminous objects
Sources of light are categorized into two main types:
- Natural Sources: Produce light naturally without human intervention (e.g., Sun, Stars, Lightning).
- Artificial (Man-made) Sources: Created by humans to produce light (e.g., Candle, Electric Bulb, Burning Wood).
Properties of Light
Light exhibits several fascinating properties. Here, we will focus on three key properties: Reflection, Refraction, and Dispersion.
Reflection of Light
What is Reflection?
Reflection is the phenomenon where light traveling in one medium strikes the surface of another medium and bounces back into the first medium.
Reflection can be of two types, depending on the surface:
- Regular (Specular) Reflection: Occurs when light reflects from smooth and shiny surfaces (e.g., a mirror), producing a clear image. All reflected rays travel in the same direction.
- Diffuse Reflection: Occurs when light reflects from rough, unpolished surfaces (e.g., a wall, wood, paper), resulting in a blurry or no image. Reflected rays scatter in many different directions.
Mirrors are excellent reflectors, enabling us to see non-luminous objects when light from a source reflects off them into our eyes.
Refraction of Light
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This phenomenon is due to refraction. Light bends as it passes from one medium (air) into another (water) because its speed changes. This bending causes our eyes to perceive the submerged part of the pencil in a different position than its actual location, making it look broken.
What is Refraction?
Refraction is the bending of light rays as they travel from one transparent medium into another, caused by a change in the light's speed.
The "hidden coin" activity (where a coin disappears when water is added to a glass) is another great demonstration of refraction. The light from the coin is refracted away from your line of sight, making the coin seem to vanish.
Dispersion of Light
What is Dispersion?
Dispersion is the process by which white light splits into its constituent colors when it passes through a medium, such as a prism or water droplets.
Figure: Dispersion of white light by a prism
When white light, like sunlight, passes through a prism, it splits into a band of seven colors known as the spectrum of white light. These colors appear in a specific order: Red, Orange, Yellow, Green, Blue, Indigo, and Violet (ROYGBIV).
Dispersion occurs because different colors (wavelengths) of light refract at slightly different angles. Violet light bends the most, while red light bends the least, causing the separation of colors. Rainbows are a spectacular natural example of dispersion, combined with reflection and refraction, occurring in water droplets.
7.2 Vision and Imaging
Purpose of Light for Vision
Light is absolutely essential for vision. Without light, our eyes would not be able to perceive our surroundings. Both a source of light and a functioning eye are critical for us to see.
Imaging
Imaging is the process of forming images. Images are formed through processes like reflection (using mirrors) or refraction (using lenses). Modern medical tools like X-rays, CT scans, ultrasounds, and MRIs are advanced imaging technologies used to visualize internal body structures for diagnosis.
Image Formation by Plane Mirror
A plane mirror, which has a flat reflecting surface, forms an image through reflection. When you look in a plane mirror, you observe a unique characteristic called Lateral inversion is the phenomenon where the left and right sides of an object appear to be reversed in its image formed by a plane mirror. For example, if you raise your right hand, your mirror image will appear to raise its left hand.lateral inversion
Key characteristics of an image formed by a plane mirror:
- The image is virtual (cannot be projected onto a screen) and erect (upright).
- The image is the same size as the object.
- The image is laterally inverted.
- The image is as far behind the mirror as the object is in front of it.
Transmission of Light through Objects
Materials interact with light in different ways, allowing us to classify them into three categories:
Transparent Materials
Materials that allow light to pass through them completely, enabling clear vision through them. Examples: Glass, clear water, air, clear plastic.
Translucent Materials
Objects that allow light to pass through partially, meaning objects cannot be seen clearly through them. Examples: Oiled paper, frosted glass, waxed paper.
Opaque Materials
Materials that completely block light from passing through them, making it impossible to see through them. Examples: Metal sheet, wood, walls, stone.
7.3 Sound
Sound is another vital form of energy that produces the sensation of hearing in our ears. This energy is primarily generated by vibrating objects. Vibration refers to the back-and-forth motion of an object, which then causes the surrounding medium to vibrate, propagating the sound.
Whether it's the strings of a musical instrument, a drum's skin, or the air column in a wind instrument, sound is produced whenever something is made to vibrate. When the vibration stops, the sound stops.