Describe a transverse wave
The vibrations in a transverse wave are perpendicular (at right angles) to the direction of energy transfer
Describe a longitudinal wave
In longitudinal waves, the vibrations are in the same direction as the energy transfer
What is the amplitude?
Amplitude is the maximum displacement of a point on the wave from its undisturbed (rest) position
What is the wavelength?
The wavelength is the distance between one point on a wave and the same point on the next wave
What is the frequency?
The frequency is the number of complete waves passing a certain point each second
What is frequency measured in?
Frequency is measured in hertz (Hz).
1 Hz is one wave per second
What is the period?
The period is the amount of time it takes for one complete wave to pass a certain point
Give examples of transverse waves
Light wave.
Ripples on the water
waves on a string
Give an example of a longitudinal wave
Sound wave
What do waves transfer?
Waves transfer energy and information without transferring matter
What is the relationship between speed, frequency, and wavelength of a wave?
Speed = frequency x wavelength
V = f x λ
What is the relationship between frequency and time period?
T = 1/f
All waves can be r_______ and r___________
Reflected and refracted
What is the law of reflection?
The angle of incidence = the angle of reflection
What is the relationship between refractive index, angle of incidence and angle of refraction?
How do you investigate the refraction of light, using rectangular blocks, semi-circular blocks and triangular prisms?
- Set up your apparatus as shown in the diagram (What diagram?) using a rectangular block.
- Shine the light ray through the glass block
- Use crosses to mark the path of the ray.
- Join up crosses with a ruler
- Draw on a normal where the ray enters the glass block
- Measure the angle of incidence and the angle of refraction and add these to your results table
- Comment on how the speed of the light has changed as the light moves between the mediums.
- Repeat this for different angles of incidence and different glass prisms.
How do you investigate the refractive index of glass, using a glass block?
- Set up your apparatus as shown in the diagram using a rectangular block.
- Shine the light ray through the glass block
- Use crosses to mark the path of the ray.
- Join up crosses with a ruler
- Draw on a normal where the ray enters the glass block
- Measure the angle of incidence and the angle of refraction and add these to your results table
- Calculate the refractive index
- Repeat steps 2 – 7 using a different angle of incidence
- Find an average of your results.
Describe the role of total internal reflection in transmitting information along optical fibres and in prisms
Total Internal Reflection:
Used to transmit signals along optical fibres.
What is critical angle C?
The angle of incidence which produces an angle of refraction of 900 (refracted ray is along the boundary of the surface).
When the angle of incidence is greater than the critical angle, total internal reflection occurs (all light is reflected at the boundary).
This effect only occurs at a boundary from a high refractive index material to a low refractive index material.
What is the relationship between critical angle and refractive index?
sin c = 1/n
What is the frequency range for human hearing?
20 - 20 000 Hz
How do you investigate the speed of sound in air?
- Use the trundle wheel to measure a distance of 100 m between two people
- One of the people should have two wooden blocks, which they will bang together above their head to generate sound waves
- The second person should have a stopwatch which they start when they see the first person banging the blocks together and stop when they hear the sound
- This should be repeated several times and an average taken for the time travelled by the sound waves
- Repeat this experiment for various distances, e.g. 120 m, 140 m, 160 m, 180 m
How can an oscilloscope and microphone can be used to display a sound wave?
With the microphone plugged into the oscilloscope and a sound incident on the microphone, the microphone will transfer the sound into an electrical signal which the oscilloscope can display.
The x axis shows the time base which can be adjusted (for example 2ms for 1 square) so time period and frequency can be calculated from this. Along the y axis voltage is displayed as the wave is converted into an electrical signal - this means amplitudes can be compared.
How can you investigate the frequency of a sound wave using an oscilloscope?
- Connect the microphone to the oscilloscope as shown in the image above
- Test the microphone displays a signal by humming
- Adjust the time base of the oscilloscope until the signal fits on the screen - ensure that multiple complete waves can be seen
- Strike the tuning fork on the edge of a hard surface to generate sound waves of a pure frequency
- Hold the tuning fork near to the microphone and observe the sound wave on the oscilloscope screen
- Freeze the image on the oscilloscope screen, or take a picture of it
- Measure and record the time period of the wave signal on the screen by counting the number of divisions for one complete wave cycle
- Repeat steps 4-6 for a variety of tuning forks
