Q.2 What is sound ? How it is produced ? [2]
Q.3 What is a transverse wave ? In which medium - solid, liquid or gas can it
be produced ? [2]
Q.4 State two properties of ultrasound that make it useful to us. [2]
Q.5 Flash of lightning reaches earlier than the sound of thunder.
Give reason. [2]
Q.6 The heart of a man beats 75 times a minute. What is its frequency and
time period?
Answers
Explanation:
2. Sound is produced when an object vibrates, creating a pressure wave. This pressure wave causes particles in the surrounding medium (air, water, or solid) to have vibrational motion. As the particles vibrate, they move nearby particles, transmitting the sound further through the medium.
3.the wave in which d particles of medium vibrate about their mean positions,in a direction perpendicular to d direction of propagation of wave is called the transverse wave. it can only be produced in solid and surface of liquids.
4.The ultrasonic waves are high frequency sound waves with smaller wavelength. These waves travel with speed equal to the speed of sound in a given medium. Their velocity remains constant in homogeneous media. These waves can produce heating effect and weld certain plastics, metals etc.
5. The reason we see a flash of lightning before hearing thunder is because light travels faster than sound. The speed of light depends on what it is moving through - being slow in gases, fast in liquids, and even quicker in solids. In the air, sound travels at around 332 metres per second.
6. Number of times it beats =75 times per minute. Hence, the time period of a man's heart beat is 0.8sec.
Answer:
2. Sound is produced when an object vibrates, creating a pressure wave. ... As the particles vibrate, they move nearby particles, transmitting the sound further through the medium. The human ear detects sound waves when vibrating air particles vibrate small parts within the ear.
3. The wave in which d particles of medium vibrate about their mean positions,in a direction perpendicular to d direction of propagation of wave is called the transverse wave. it can only be produced in solid and surface of liquids..
4. The following are the main properties of ultrasonic waves:
- The ultrasonic waves cannot travel through vacuum.
- The ultrasonic waves are high frequency sound waves with smaller wavelength.
- These waves travel with speed equal to the speed of sound in a given medium.
- Their velocity remains constant in homogeneous media.
5. Lightning is seen earlier and thunder is heard later because the speed of sound is 330 m/s and the speed of light is 300,000,000 m/s. Light travels faster than a sound. Thus, light from the lightning reaches first to you. The sound from the lightning takes longer to reach and hence heard later.
6. 75 beats/60 seconds = 1.25 beats per second which can be expressed as 1.25 Hz. The time period of the heart beat is an expression of seconds per beat (the duration of each heartbeat). 60 seconds/75 beats = 0.8 seconds per beat.