WAVE || Class 9 Science Notes

WAVE

1. Short answer type questions:               

a. Write the relation between wavelength, frequency and velocity for a sound wave.

= The number of vibrations per second is known as frequency.

= The wavelength seems to be the shortest distance over which the wave be repeated.

→ The velocity of a wave would be the distance it. may travel in one second.

→The relation between wavelength, frequency and -velocity is λ = V x T.

b. Write a use of ultrasonic sound. 

→ It is used to visualise the internal structures of the human body. 

c. Define electromagnetic spectrum. 

→ The band of all electromagnetic waves according to the increasing wavelength is called an electromagnetic spectrum.

d. What is visible light? 

= Visible light is portion of the electromagnetic spectrum that is visible to the human eye.  

e. Define radio waves.

= Radio waves. are electromagnetic waves with the longest wavelengths.

f. Write any two Medical Imaging uses of X-rays Radiation Therapy.

= i. Medical Imaging

   ii. Radiation Therapy

g. Define wave.

= The path of energy is called a wave.

h. What is the wavelength of radio wave? 

= The wavelength of radio wave is about 10^-1m to 10^3m.

i. Which technology is used to take the image internal organs without using electromagnetic waves? 

= Ultrasonography technology is used to take the image internal organs without using electromagnetic waves.

j. What will be the effect on the wavelength of sound wave if the pitch of the sound is increased? 

= The wavelength of a sound wave decreases as the pitch of the sound increases. This is because higher pitched sound has a higher frequency, and frequency is inversely proportional to wavelength.

2. Long answer type question.

a. How is a a sound wave produced? 

→ Sound wave is produced when vibrates, creating a pressure wave.

b. On what conditions does an echo take place? 

= An echo take place when the distance between. the source of sound and the reflecting surface. should be is 17 m.

c. Write the merits and demerits of ultraviolet.

→ The merits of ultraviolet rays are:

i. Production of Vitamin D.

ii. Improvement in mood.

iii. Increased energy 

*The demerits of ultraviolet rays are:

i. It causes sun tanning of the skin due to the radiation from the sun.

d. Why are radio way waves not harmful to us? 

→Radio waves are not harmful to us because they didn't have enough energy to damage DNA directly.      

e. Name the sequence of colours from up to down a spectrum.

= Violet, Indigo, blue, green, yellow, orange, and red.

f. Write three of reflection of sound. 

= i. It is used to identify presence of an an iceberg the way of a ship. 

ii. It is used to know the depth of an ocean.

 iii. It is used to make musical programs melodious by creating reverberation.

g. Describe computerized tomography in short. 

= CT scans are very common in medical treatments for the diagnosis of disease. A CT combines data from several X-rays to detailed image of structures inside produce the body and produces 2 dimensional or 3 dimensional images of section of the body.      

h. Describe X-ray imaging in short and it with sonography. 

= X-ray compare are used widely in the medical field to take the photographs of the internal organs. X-ray imaging is done or image is located between X-ray source and on X-ray detector. When the rays passes through the body and are absorbed in different amount by different tissues, but some dense organs like bones having higher radiological density are readily absorbed by x-rays then, as a result bony structure appers whiter than other tissue on sheet or radiograph. X-ray imaging is done by using x-ray machine and a computerized tomography scanner while sonography doesn't use any x-rays to take image of internal. organs.

3. Give reasons:

a. The wall and the ceiling of a cinema hall are covered with sound absorbing materials.

= Because to reduce reverberation, to listen round melodious

b. Echo is experienced more is a newly constructed room than in a furnished room. 

= Because furniture acts as material medium to reduce reverberation.

c. Reflection sound (echo) is faither than the original sound. 

= Because this is due to the fact that the sound is absorbed by the medium through which is passes during reflection..

d. Astronauts use an electronic medium in space to talk to each other.

= Because there is no air in moon, or space and the sound there needs some material medium to propagate.

e. Frequent X-ray imaging and CT manning are not good for health. 

= Because radiation produced by those machines are. harmful to our internal organs.

f. During CT scanning of a patient, he/she enter in an arc.

Because so that the scanner can collect data from the different sides of an organ for the series of image formation.

g. Ultrasound can pass over through solids.

= Ultra sound can pass even solids because of its high frequency.   

4. Differentiate between:

a. A longitudinal 

i. It speed is less. 

ii. These waves can be produced in gas.

iii. Material medium is needed for transmission.

* Transverse waves 

i. It speed is more. 

ii. These wave can't be produced in gat

iii. Non-material medium required for its transmission.

b. Mechanical wave 

i. It can be produced by only in material medium.

ii. It's speed is very less relative to electromagnetic wave.

* Electromagnetic wave

i. It doesn`t require only material medium for its propagation.

ii. It`s speed is high as compared to mechanical wave.

c. Compressions 

i. In compressions the particles get compressed. 

ii. Density is more than normal density.

* Rarefactions

i. In rarefactions the particles are loosely packed. 

ii. In rarefractions, density is less than normal density.   

d. Echo

i. The repitition of sound which is reflected from the walls of a large room or distant surface is called echo. 

ii. It is heared in fields or halls open fields or halls.

* Reverberation

i. Distance between source and reflector should be less than 17m.

ii. It is heared in an empty room or hall.

e. Ultraviolet rays 

i. It's wave length ranges from 4x10^-9 m to 10^-8m.

ii. It can be detected by photographic films. 

iii. The UV waves vitamin D in our skin.

* Infrared rays

i. Its wave length ranges between 7*10^-7m to 10^3m.

ii. It can be detected by a sensitive thermometer.

iii. It is used as a source of heat.

f. Sound wave

i. Its velocity is less than light wave.

ii. It needs material medium to propagate.

* Light wave

i. Its velocity is much more than sound wave.

ii. It can propagate through vaccum too.