Solve the crossword puzzle. Across → sound of frequencies above 20 kHz . amplitude of sound. ring of cartilage. unpleasant sound. reciprocal of time period. Down ↓ form of energy produced due to vibrations. voice box. SI unit of frequency. sound of frequencies below 20 Hz . shrillness or flatness of sound.

Across → 1. The sounds of frequencies higher than 20 kHz are called ‘ultrasonic sounds’ (or just ‘ultrasound’). Humans cannot hear these frequencies of sound. For humans, the audible range of sound is between 20 Hz to 20 , 000 Hz . 2. Amplitude: Maximum displacement of any wave-particle about its mean position is nothing but its amplitude. The amplitude of a sound wave decided its loudness or volume. If a wave has a larger amplitude means it has a louder sound, and a smaller amplitude means has a softer sound. 3. Birds have a ring of cartilage, called syrinx, in their wind pipe. They use it (instead of the vocal cords) in their voice box to produce their characteristics sound. This characteristic sound is a jarring, or unpleasant one. 4. The unwanted sound that is loud and unpleasant is called noise. The sounds from loudspeakers, vehicles, traffic, etc., lead to noise pollution. Noise can badly affect our ears and can lead to deafness. 5. Frequency of a vibrating body is defined as the number of vibrations in one second. Frequency of a wave is defined as the number of times the wave pattern is repeated in the time-interval of one second. It is reciprocal of time period. Its SI unit is hertz. Down ↓ 1. A sound is a form of energy which produces the sensation of hearing. Sound is defined as vibrations that travel through the air or another medium as an audible mechanical wave. It is produced from a vibrating body. It is a longitudinal wave. We know that sound waves require a material medium for their propagation. The vibrating body causes the medium (water, air, etc.) around it to vibrate thus producing sound. 2.Sound is produced in the human beings in the voice box which is called 'larynx'. It is situated in our throat at the top of the wind-pipe (or trachea). The human voice box contains two ligaments known as vocal cords, this vibrates to produce sound. 3.The SI unit of frequency is hertz ( Hz ) . Note: The number of vibrations or oscillations occurring in unit time is known as the frequency of the wave. Frequency is the reciprocal of time period. ν = 1 T . 4. Humans can only hear sound waves as distinct pitches when the frequency lies between about 20 Hz and 20 KHz. Sound waves below 20 Hz are known as infrasonic sound. Different animals species have varying Hearing ranges. 5. Sound is produced from a vibrating object. Sound produced from any source has three characteristics-pitch, loudness and quality. Pitch of a sound is also known as shrillness. The pitch of a sound depends on its frequency. Higher is the frequency, higher is the pitch of the sound produced.