Light Energy and Sound Energy Class 4 Science - Orchids
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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.
shadow

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.
length-of-a-shadow-throughout-the-day

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.
blue-sky

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.
rainbow

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.
burning-with-a-glass

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.
sound-waves

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
  • The sound of firecrackers.
  • The sound of television at high volumes.
  • The sound of water coolers.
  • The sound of a whistle.
  • The sound of a guitar.
  • The sound produced by a mouth organ.

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.
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