Light Energy and Sound Energy
- Light energy and sound energy are various forms of energy.
- Light does not require a medium to travel, whereas sound needs a medium to travel.
- The speed of light is faster than the speed of sound. For the same reason, we hear the sound of thunder after seeing a lightning strike.
- The particles in the solid medium are situated very closely that is why sound travels faster in solids and slowest in gases.
Sources and Properties of Light
Question 1:
How are Shadows Formed?
Answers:
- A shadow is a dark figure formed when an opaque object blocks the path of light.
- The source of the light, an opaque object and a screen are three basic requirements for the formation of a shadow.
- A shadow is always black in colour. Its size depends on the distance between the object and the light source.
Question 2:
Explain How Shadows Change Throughout the Day?
Answers:
- Shadows are longer in the morning and evening, and shorter during the day.
- The size of a shadow depends on the sun's position in the sky.
- The sun is near the horizon during sunrise and sunset, which makes the shadows longer.
- In the afternoon, the sun is over our heads; hence the shadows are smaller.
Question 3:
Why Does the Sky Appear Blue?
Answers:
- When sunlight passes through the atmosphere, tiny air particles of the atmosphere scatter the light waves.
- These particles scatter blue light more than other colours, making the sky appear blue.
Question 4:
What Is a Rainbow, and How Is It Formed?
Answers:
- A multi-coloured arc that appears in the sky due to the dispersion of light through water droplets is called a rainbow.
- Dispersion of light is the splitting of white light into seven constituent colours.
- Rainbow is formed after the rain due to the dispersion of sunlight by the water particles.
- The order of seven colours in the rainbow are violet, indigo, blue, green, yellow, orange, and red.
Question 5:
How Does a Magnifying Glass Burn Things?
Answers:
- A magnifying glass is made using a convex lens.
- A convex lens is thicker in the middle and thinner at the edges and has the ability to converge the light rays passing through it at one point.
- Due to the high concentration of light rays at a point, sufficient heat is produced, which can burn things.
Sources and Properties of Sound
Question 1:
How Do Sound Waves Travel Through the Air?
Answers:
- Air is made up of molecules which have space between them.
- Soundwaves, while travelling through air, strike these molecules to produce vibrations which are transferred to the adjacent molecules.
- This phenomenon allows sound waves to travel through the air gradually.
- This process is quick and is completed in fractions of a second.
Question 2:
Why Do Sound Waves Travel Faster in Water Than in the Air?
Answers:
- The lesser the space between the atoms or molecules, the faster propagation of sound.
- The atoms in water are comparatively closer than the atoms in the air. Hence, sound travels faster in water.
Question 3:
Which Property of Sound Determines Its Loudness?
Answers:
- Amplitude is the property of sound that determines its loudness.
- It is the maximum limit of the vibration produced by an object.
- Higher the amplitude, the higher the loudness.
Question 4:
- Categorise the Following Into Noise and Music—
- The Sound of Firecrackers.
- The Sound of a Guitar.
- The Sound of Television at High Volumes.
- The Sound of Water Coolers.
- The Sound of a Whistle.
- The Sound Produced by a Mouth Organ.
Answer:
The sound which is loud and unpleasant is categorised as noise.
| Noise | Music |
|---|---|
|
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Question 5:
Why Is a Female Voice Shriller Than a Male Voice?
Answer:
- Voice is produced from vocal cords that are located in our throat region.
- These vocal cords are thin flaps of cartilage.
- These flaps of cartilage are thinner in females than in males.
- A thinner object can vibrate faster than a thicker object and is able to produce a high-pitched sound.
- Thus, the sound made by a female is shriller than that of a male.