Summary Class 8-10 science explanation(Don't miss!)

Sound
Main Concepts
Sound- It is the vibration caused by any object in this world which
travels through medium and that we can hear using our ear. Note-
Sound needs medium to travel. Sound cannot travel without medium. It
can be any medium from air to water.
Medium Needed- Solid > Liquid > Gas . Sound can’t travel in vacuum.
Pitch- It is the frequency at which sound travels. Hz is the measurement
of pitch. Higher the Hz more the shrill sound.

10 Key Facts
 Speed: Air 340m/s, Water 1500m/s, Steel 5000m/s
 Frequency > 20kHz = Ultrasound
 < 20Hz = Infrasound
 Echo = Reflection (min distance 17m)
 Reverberation = Multiple reflections (bad for halls)
 SONAR = Sound Navigation Ranging (ocean depth)
 Human ear: 20Hz-20kHz
 Loudness = Amplitude
 Quality = Waveform shape
 Doppler effect = Pitch change (train horn higher when
approaching)

6 Exam MCQs
1. Sound needs: (a) vacuum (b) medium ✓
2. Fastest medium: (a) air (b) steel ✓
3. Ultrasound: (a) <20Hz (b) >20kHz ✓
4. Echo distance: (a) 17m ✓ (b) 34m
5. SONAR measures: (a) distance ✓ (b) frequency
6. Ear range: (a) 20-20kHz ✓ (b) 10-10kHz

Quick Revision
 Trick: Speed: Steel>Water>Air
 Pitch=Freq Loudness=Amplitude
 Exam Diagram: Draw human ear (5 marks)