1. 13/10/2015 Physics 3 Sound

2. 13/10/2015 How sound travels… As we know, sound waves are formed when something vibrates. But how does the sound reach our ears? 1) An object makes a sound by vibrating 2) The vibrations pass through air by making air molecules vibrate 3) These vibrations are picked up by the ear Air molecules

3. 13/10/2015 Sound can be reflected and refracted Bats use echoes to locate insects. They time how long the echo takes to come back and use that to locate the insect An Echo is a reflected sound wave Echolocation is also used in the shipping industry but remember Sound in air = 330m/s Sound in water = 1500m/s

4. 13/10/2015 Sound is also refracted In the day the hot ground warms the air and sound waves travel faster. This makes the waves refract upwards At night the air is colder by the ground so the sound waves are refracted towards the ground This is why you can here sound from a greater distance at night

5. 13/10/2015 Using an oscilloscope 1) Quiet sound, low frequency: 2) Quiet sound, high frequency: 3) Loud sound, low frequency: 4) Loud sound, high frequency:

6. 13/10/2015 1)Pre-natal scanning 2)Cleaning – it can be used to dislodge dirt 3)Detecting flaws or cracks 4)Medical treatmentUltrasound Ultrasound is the region of sound above 20,000Hz – it can’t be heard by humans. There are a number of uses for ultrasound:

7. 13/10/2015 How does ultrasound work? Ultrasonic waves are partly _________ at the boundary as they pass from one _______ to another. The time taken for these reflections can be used to measure the _______ of the reflecting surface and this information is used to build up a __________ of the object. Words – depth, reflected, picture, medium

8. 13/10/2015 Using an oscilloscope with ultrasound Consider a block of metal with a flaw: 20ms/div Q. If the speed of the ultrasonic wave is 3,000m/s how far away is the flaw from the detector?