Grade 9||Wave|| Notes

1. What is a Wave?

A wave is a periodic disturbance that transmits energy from one place to another without the transfer of matter.

Examples:

1. Water waves
2. Sound waves
3. Light waves
4. Earthquake waves

2. Use of Waves

We are surrounded by different types of waves. Waves strike our bodies all the time.
We use:

1. Light waves for vision
2. Heat waves from the sun
3. Radio waves for FM radio
4. Waves in mobile phones, Wi-Fi, Bluetooth
5. X-rays and sound waves in medical diagnosis

A network of waves is used for:

1. Communication
2. Security checking
3. Distance measurement
4. Medical diagnosis

3. Types of Waves

(A) Mechanical Waves

1. Require a medium to travel
2. Energy decreases due to absorption by the medium
3. Examples: Sound wave, water wave

Mechanical waves are of two types:

1. Longitudinal wave
2. Transverse wave

(B) Electromagnetic Waves

1. Do not require a medium
2. Can travel through vacuum
3. Energy is conserved
4. Travel at the speed of light
5. Examples: Light, radio waves, X-rays

4. Longitudinal Wave

1. Direction of vibration is parallel to direction of wave
2. Transmitted as compression and rarefaction
3. Compression: molecules close together
4. Rarefaction: molecules far apart
5. Example: Sound wave
6. Occur in solid, liquid and gas

5. Transverse Wave

1. Direction of vibration is perpendicular to direction of wave
2. Transmitted as crest and trough
3. Crest: raised part
4. Trough: depressed part
5. Example: Water surface wave, rope wave
6. Occur in solid and liquid only, not gas

6. Wave Terminologies (VERY IMPORTANT)

Amplitude: Maximum displacement from mean position

Frequency (f): Number of waves produced per second

SI unit: Hertz (Hz)

Time Period (T): Time taken to produce one complete wave

T = 1 / f

Wavelength (λ):

Distance between two nearest compressions

Or two nearest rarefactions

Or two nearest crests

Wave Velocity (v):

7. Mechanical Wave vs Electromagnetic Wave

Mechanical WaveElectromagnetic WaveNeeds mediumNo medium neededEnergy decreasesEnergy conservedSpeed varies with mediumConstant speedExample: soundExample: light

8. Electromagnetic Spectrum

The electromagnetic spectrum is the complete range of electromagnetic waves from lowest frequency to highest frequency.

Order:
Radio → Microwave → Infrared → Visible → Ultraviolet → X-ray → Gamma ray

Radio waves: longest wavelength, least energy

Gamma rays: shortest wavelength, highest energy

9. Applications of Electromagnetic Waves

Radio Waves

1. Radio and TV broadcasting
2. Radio telescope
3. Safe for living beings

Microwaves

1. Cooking food in microwave oven
2. Radar communication
3. Airport surveillance
4. Speed guns
5. Mobile phones, Wi-Fi, Bluetooth, satellites

Infrared Rays

1. Produce heat sensation
2. Infrared heaters
3. Remote control devices
4. Thermal imaging cameras
5. Night vision cameras
6. Astronomy observation

Visible Light

1. Helps us see objects
2. Photosynthesis in plants
3. Display screens
4. Optical fiber communication
5. Red light: longest wavelength
6. Violet light: shortest wavelength

Ultraviolet Rays

1. Causes sunburn
2. High exposure causes skin cancer
3. Used in sterilization
4. Vitamin D formation
5. CFL lamps glow due to UV rays
6. Water purification (SODIS)

X-Rays

1. Penetrate soft tissues
2. Bones absorb more X-rays
3. Used to detect fractures
4. CT scan
5. Airport security scanners
6. Cancer treatment
7. Harmful in high exposure

Gamma Rays

1. Produced during radioactivity
2. Highly energetic
3. Dangerous
4. Used in radiotherapy
5. Sterilization of food and equipment
6. Nuclear medicine

10. Reflection of Sound

The sound wave that returns after striking a rigid surface is called reflected sound.

Echo is reflected sound heard after some time.

11. Uses of Reflection of Sound

1. Echolocation in bats and dolphins
2. SONAR
3. Distance measurement
4. Ultrasonic ruler
5. Ultrasonography
6. Burglar alarms
7. Car parking sensors

13. Ultrasound

Sound having frequency greater than 20,000 Hz is called ultrasound.
Human ear cannot hear it.

14. Ultrasonography

1. Uses ultrasound waves
2. Uses transducer
3. Produces sonogram
4. Safe for fetus
5. Used to check:
6. Pregnancy
7. Tumors
8. Kidney stones
9. Heart function (echocardiography)

15. X-Ray Imaging

1. Uses X-rays
2. Bones appear white
3. Soft tissues appear grey
4. Air-filled organs appear black
5. Used for fractures, tumors, infections
6. Discovered by Wilhelm Roentgen (1895)

16. CT Scan

1. Advanced X-ray technology
2. Rotating X-ray source
3. Produces 2D and 3D images
4. Shows soft tissues clearly
5. Used to detect internal injuries, blood clots, tumors

17. Acoustic Protection

1. Use of soft and porous materials
2. Absorbs sound
3. Reduces echo
4. Used in:
5. Cinema halls
6. Music rooms
7. Recording studios
8. Seminar halls

18. Role of Electromagnetic Waves in Modern Life 

1. Communication (radio, TV, mobile)
2. Medical diagnosis (X-ray, CT scan)
3. Cooking (microwave oven)
4. Security systems
5. Astronomy
6. Remote sensing
7. Daily life technology