Section 3: Waves
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a) Units
3.1: Use the following units: degree (°), hertz (Hz), meter (m), meter per second (m/s), second (s)
Degree: Used to measure temperature or angles
Hertz: Used to measure frequency
Meter: Used to measure distance
Meter per second: Used to measure distance in a given period of time
Second: Used to measure time
Degree: Used to measure temperature or angles
Hertz: Used to measure frequency
Meter: Used to measure distance
Meter per second: Used to measure distance in a given period of time
Second: Used to measure time
b) Properties of waves
3.2: Understand the differences between longitudinal and transverse waves and describe experiments to show longitudinal and transverse waves in, for example, ropes, springs and water
Transverse Waves
A transverse wave vibrates at right angles to the direction in which the wave is moving (e.g. light waves or water waves)
A longitudinal wave vibrates along the direction in which the wave is moving (e.g. sound waves)
Transverse Waves
A transverse wave vibrates at right angles to the direction in which the wave is moving (e.g. light waves or water waves)
- Waggle one end of a slinky from side to side
- You will see the waves traveling through it
A longitudinal wave vibrates along the direction in which the wave is moving (e.g. sound waves)
- Push and pull a slinky in a direction parallel to its axis
- You will see the waves traveling through it
3.3: Define amplitude, frequency, wavelength and period of a wave
Amplitude (A): Amplitude is the maximum movement of particles from their resting position caused by a wave
Frequency (f): Frequency is the number of waves produced in a given period of time by a source
Wavelength (λ): The distance between the crests of a wave
Period of a wave (T): The time period between two waves
Amplitude (A): Amplitude is the maximum movement of particles from their resting position caused by a wave
Frequency (f): Frequency is the number of waves produced in a given period of time by a source
Wavelength (λ): The distance between the crests of a wave
Period of a wave (T): The time period between two waves
3.4: Understand that waves transfer energy and information without transferring matter
Waves are able to transfer energy and information without transferring matter. For example, if you are pushing a swing, you are able to transfer energy to it without expelling any of your body matter.
Waves are able to transfer energy and information without transferring matter. For example, if you are pushing a swing, you are able to transfer energy to it without expelling any of your body matter.
3.5: Know and use the relationship between the speed, frequency and wavelength of a wave
Wave Speed = Frequency x Wavelength
v = f x λ
Wave Speed = Frequency x Wavelength
v = f x λ
3.6: Use the relationship between frequency and time period
Frequency = 1 / Time Period
f = 1 / T
Frequency = 1 / Time Period
f = 1 / T
3.7: Use the above relationships in different contexts including sound waves and electromagnetic waves
v = f x λ and f = 1 / T can be used to solve problems related to sound waves and electromagnetic waves
v = f x λ and f = 1 / T can be used to solve problems related to sound waves and electromagnetic waves
3.8: Understand that waves can be diffracted when they pass an edge
Diffraction is a property that is demonstrated by all waves. Diffraction is the spreading out of waves, for example when they pass an edge.
Diffraction is a property that is demonstrated by all waves. Diffraction is the spreading out of waves, for example when they pass an edge.
3.9: Understand that waves can be diffracted through gaps, and that the extent of diffraction depends on the wavelength and the physical dimension of the gap
Waves can also be diffract through gaps. If the gap is large, then the majority of the waves passing through continue in a straight line. There are regions to the left and right of the gap where there are no waves. But if the size of the gap is adjusted so that it is equal to the wavelength of the waves, the waves spread out in every direction.
Waves can also be diffract through gaps. If the gap is large, then the majority of the waves passing through continue in a straight line. There are regions to the left and right of the gap where there are no waves. But if the size of the gap is adjusted so that it is equal to the wavelength of the waves, the waves spread out in every direction.
c) The electromagnetic spectrum
3.10: Understand that light is part of a continuous electromagnetic spectrum which includes radio waves, microwaves, infrared radiation, visible light, ultraviolet light, x-ray, and gamma ray radiations and that all these waves travel at the same speed in free space
Light is made up of the electromagnetic spectrum, which includes seven different types of waves. All these waves travel at the speed of light in a vacuum (300,000,000m/s). They are all transverse waves, they all transfer energy, and they can all be reflected refracted and diffracted.
Light is made up of the electromagnetic spectrum, which includes seven different types of waves. All these waves travel at the speed of light in a vacuum (300,000,000m/s). They are all transverse waves, they all transfer energy, and they can all be reflected refracted and diffracted.
3.11: Identify the order of the electromagnetic spectrum in terms of decreasing wavelength and increasing frequency, including the colors of the visible spectrum
3.12: Explain some of the uses of the electromagnetic spectrum
- radio waves: broadcasting and communications
- microwaves: cooking and satellite transmissions
- infrared: heaters and night vision equipment
- visible light: optical fibres and photography
- ultraviolet light: fluorescent lamps
- x-rays: observing the internal structure of objects and materials and medical applications
- gamma rays: sterilizing food and medical equipment
3.13: Understand the harmful effects of excessive exposure of the human body to electromagnetic waves
- microwaves: internal heating of body tissue
- infrared: skin burns
- ultraviolet light: damage to surface cells and blindness
- gamma rays: cancer cells and mutation
d) Light and sound
3.14: Understand that light waves are transverse waves which can be reflected, refracted and diffracted
Light waves are all transverse waves which can be reflected (thrown back), refracted (reflected indirectly) and diffracted (spread out).
Light waves are all transverse waves which can be reflected (thrown back), refracted (reflected indirectly) and diffracted (spread out).
3.15: Use the law of reflection
The angle of incidence is equal to the angle of reflection
The angle of incidence is equal to the angle of reflection
3.16: Construct ray diagrams to illustrate the formation of a virtual image in a plane mirror
3.17: Describe experiments to investigate the refraction of light, using rectangular blocks, semicircular blocks, and triangular prisms
- Place a block of glass on a piece of paper and draw an outline of it
- Draw the normal
- Draw a line at 30° to the normal and shine a ray of light down it
- Draw a line where the light comes out of the other side (emergent ray) and connect the two lines
- Measure the angle of the emergent ray
- Repeat with different shaped glass blocks
3.18: Know and use the relationship between refractive index, angle of incidence and angle of refraction
n = sin i / sin r
n = sin i / sin r
3.19: Describe an experiment to determine the refractive index of glass, using a glass block
- Place a glass block on a piece of paper and draw an outline of it
- Draw the normal
- Draw lines at varying degrees to the normal (0° - 90°) and shine a ray of light down them one by one
- Draw lines where the light comes out of the other side (emergent ray) for each angle and connect the respective lines
- Measure the angle of the emergent ray
- Use the relationship between refractive index, angle of incidence and angle of refraction to calculate the refractive index for each angle
3.20: Describe the role of total internal reflection in transmitting information along optical fibers and in prisms
Total internal reflection can occur if the angle made by the rays is greater than c. In glass the critical angle is around 42° . As the angle of reflection is greater than 42°, total internal reflection can occur. One of the most important applications for total internal reflection is the optical fibre. This is a very thin strand composed of two different types of glass. There is a central core of optically dense glass which has a high refractive index. There is a coat of less optically dense glass around it. Light entering the inner core of the narrow fibers always strikes the boundary of the two glasses at an angle greater than the critical angle. No light escapes across this boundary. The fibre therefore acts as a 'light pipe' providing a path that the light follows even when the fibre is curved. Another important application for total internal reflection is in prismatic periscopes as shown in the image on the right. |
3.21: Explain the meaning of critical angle c
The critical angle is the angle of incidence at which maximum refraction occurs.
The critical angle is the angle of incidence at which maximum refraction occurs.
3.22: Know and use the relationship between critical angle and refractive index
sin c = 1 / n
sin c = 1 / n
3.23: Understand the difference between analog and digital signals
- An analog signal is where a signal is converted into electrical charges that vary continuously
- A digital signal is where a signal is converted into binary code
3.24: Describe the advantages of using digital signals rather than analog signals
Advantages of digital signals:
Advantages of digital signals:
- Regeneration of digital signals creates a clean accurate copy of the original signal
- Digital systems are easier to design and build
- Digital systems deal with data that is easy to process
- Digital signals can be copied accurately unlimited times
3.25: Describe how digital signals can carry more information
Analog and digital signals carry the same amount of information, but analog signals are easily distorted and when regenerated, they are accompanied by unwanted sounds. Eventually this unwanted sound may drown out the original signal or introduce errors in the information. Digital signals do not have these problems as they are made of binary code (i.e. zeroes and ones).
Analog and digital signals carry the same amount of information, but analog signals are easily distorted and when regenerated, they are accompanied by unwanted sounds. Eventually this unwanted sound may drown out the original signal or introduce errors in the information. Digital signals do not have these problems as they are made of binary code (i.e. zeroes and ones).
3.26: Understand that sound waves are longitudinal waves and how they can be reflected, refracted and diffracted
Sound waves can be reflected, refracted and diffracted in the same way as light waves. For example, an echo is a reflection of sound.
Sound waves can be reflected, refracted and diffracted in the same way as light waves. For example, an echo is a reflection of sound.
3.27: Understand that the frequency range for human hearing is 20 Hz - 20,000 Hz
The frequency range for human hearing is 20 Hz - 20,000 Hz. This means that the human ear cannot hear sounds that have a lower frequency than 20 Hz or a higher frequency than 20,000 Hz.
The frequency range for human hearing is 20 Hz - 20,000 Hz. This means that the human ear cannot hear sounds that have a lower frequency than 20 Hz or a higher frequency than 20,000 Hz.
3.28: Describe an experiment to measure the speed of sound in air
- Measure the distance between two places
- Have a sound made in one place
- Start the stopwatch when the sound is made
- Stop the stopwatch when the sound is heard
- Use the relationship between speed, distance and time to calculate the speed of the sound
3.29: Understand how an oscilloscope and microphone can be used to display a sound wave
- Your vocal chords emit sound waves
- The microphone converts these waves into digital electrical waves
- The frequency, wavelength and amplitude of these waves is displayed on an oscilloscope
3.30: Describe an experiment using an oscilloscope to determine the frequency of a sound wave
- Connect the oscilloscope to a device that emits sound
- Adjusting the frequency meter on the device will display different frequencies on the oscilloscope
3.31: Relate the pitch of a sound to the frequency of vibration of the source
The more the sound source vibrates, the higher the pitch of the sound
The more the sound source vibrates, the higher the pitch of the sound
3.32: Relate the loudness of a sound to the amplitude of vibration
The higher the amplitude of the vibration, the louder the sound
The higher the amplitude of the vibration, the louder the sound