Lesson 7 - Uses of Ultrasound

(Set 1 only)

Ultrasound, frequency, boundary, reflection

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Ultrasound, frequency, boundary, reflection

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• Start
• Recall questions
• Main
• Discuss uses of ultrasound and how the ultrasound works.
• Ultrasound calculates distance. How do we calculate distance? What would we need to measure - discuss speed of sound in different media. Exam question
• Learning check- explain uses of ultrasound, use physics textbook to help.
• Plenary
• Exam question - the exam question is 19 marks, so ensure you leave enough time for it to be completed and self marked.
• Alternative questions if you don’t want to do the 19 mark Q.

Ultrasound, frequency, boundary, reflection

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Practical / Demo - No demos or practicals in this lesson

Safety

• Key safety point / equipment required

Aim

• Key teaching points

Top tips

• Things to do to make sure it works well

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Method

• Step by step instructions

Ultrasound, frequency, boundary, reflection

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Ultrasound, frequency, boundary, reflection

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Ultrasound, frequency, boundary, reflection

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Lesson 7 - Uses of Ultrasound

Answer in your book:

Give the upper frequency limit of human hearing.

Explain the difference between transverse and longitudinal waves.

Calculate the speed of a sound wave of wavelength 10cm and frequency 3.4kHz.

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Ultrasound, frequency, boundary, reflection

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Lesson 7 - Uses of Ultrasound

Check your answers:

Give the upper frequency limit of human hearing. 20 kHz

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Explain the difference between transverse and longitudinal waves.

Transverse waves oscillate perpendicular to the direction of energy travel and do not require particles to propagate. Longitudinal waves oscillate parallel to the direction of energy travel and do require particles to propagate.

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Ultrasound, frequency, boundary, reflection

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Lesson 7 - Uses of Ultrasound

Check your answers:

Calculate the speed of a sound wave of wavelength 10 cm and frequency 3.4kHz.

Speed = frequency X wavelength

Speed = 3400 X 0.1

Speed = 340 m/s

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Ultrasound, frequency, boundary, reflection

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Lesson 7 - Uses of Ultrasound

Learning Objectives:

Describe ultrasound and audible sound waves in terms of frequency.

Explain how ultrasound can be used in distance measurement.

Calculate the positions of objects or flaws in metal objects using data from an ultrasound trace.

Ultrasound, frequency, boundary, reflection

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What is ultrasound?

Sound with a frequency above the upper limit of human hearing, 20kHz.

Ultrasound, frequency, boundary, reflection

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How can ultrasound be used?

Prenatal and other medical scans

Medical treatments

Non destructive testing (looking for cracks in objects)

Echo location

Ultrasound, frequency, boundary, reflection

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How does an ultrasound scanner work?

Ultrasound, frequency, boundary, reflection

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Medical scanning

1. A transducer is placed against the skin and emits ultrasound waves.
2. The ultrasound waves are partially reflected at a boundary between different types of tissue.
3. The reflected ultrasound waves are picked up by the transducer.
4. Using the time for the pulse to return and speed of sound in different tissues, the distance to the boundaries is calculated.
5. This information is used to create an image on a screen.

Ultrasound, frequency, boundary, reflection

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Advantages of ultrasound imaging

• Ultrasound waves are reflected at the boundaries between soft tissues so we can use them to create images of organs in the body.
• Ultrasound waves do not have enough energy to ionise atoms (unlike X-Rays) so it is harmless.

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Ultrasound, frequency, boundary, reflection

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Other medical uses of ultrasound:

• Kidney stones are solid crystals formed from substances found in urine. They can sometimes build up into large stones inside the kidney. These can then pass into the urethra and cause a blockage, accompanied by severe pain.

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• High frequency ultrasound waves focused at a kidney stone cause it to vibrate, breaking it into small enough pieces to pass out in the urine.

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Ultrasound, frequency, boundary, reflection

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Industrial uses of ultrasound waves:

Non destructive testing

Looking for cracks in metal components.

• This block has 2 cracks in it.
• What would it look like if it was perfect?

It would only show the transmitted pulse and the far-side reflected pulse.

Ultrasound, frequency, boundary, reflection

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Echolocation

Ships and submarines can use ultrasound to detect objects in deep water. It can be used to measure the water depth below a ship.

The pulses from a transmitter are reflected off the sea bed below the ship and detected by a receiver at the same depth as the transmitter.

How can the distance be calculated?

Ultrasound, frequency, boundary, reflection

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Calculating distance using ultrasound

What two quantities do we need to know in order to calculate distance?

Depth of boundary below surface (m) = ½ x speed of ultrasound wave (m/s) x time (s)

distance = speed x time

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distance travelled by wave (m) = speed of ultrasound wave (m/s) x time (s)

Ultrasound, frequency, boundary, reflection

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Exam Question

Ultrasound, frequency, boundary, reflection

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Check your answers

Ultrasound, frequency, boundary, reflection

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Learning check:

Give 3 uses of ultrasound waves and explain each one.

Use pages 183 to 185 of the Physics textbook to help you.

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Ultrasound, frequency, boundary, reflection

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Exam question

19 marks = 19 minutes

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Exam technique: When a section of a question is worth a large number of marks (6 in this case) you need to ensure you write a sufficient amount of information to earn all the marks.

In part f(i) in this question you need to make 6 points to gain all 6 marks.

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Check your notes:

Ultrasound, frequency, boundary, reflection

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Remember to show your working.

Ultrasound, frequency, boundary, reflection

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Remember to show your working.

Ultrasound, frequency, boundary, reflection

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Check your answers

3. a) 170 X 2 = 340 metres

b) t = d / s = 340 / 340 = 1s. The sound is heard 1 second later

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4. Time to travel from the bat to the wall is half of the total time = 0. 1s,

Distance = speed X time = 340 X 0.1 = 34 metres

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5. a) Time is half the time for echo to return = 0.2 seconds

Distance = speed X time = 1500 X 0.2 = 300 metres

b) 𝝀 = s / f = 1500 / 30000 = 0.05 metres

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Questions on the sheet start at number 3

Ultrasound, frequency, boundary, reflection

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Check your answers

6. a) Calculate speed for both situations, then work out the average of the two.

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speed = distance / time

speed = 1000 / 3.1 speed = 1000 / 2.9

speed = 322.58 m/s speed = 344.83 m/s

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Average speed = (322.58 + 344.83) / 2

Average speed = 333.7 m/s

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b) The two different times could be due to:

Measurement errors

A strong wind blowing from East to West

The fireworks exploding at different heights above the ground.

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Ultrasound, frequency, boundary, reflection

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Logos / symbols

Ultrasound, frequency, boundary, reflection

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