Physics 3 - Waves Flashcards
3.1 List the units and unit symbols for: frequency
hertz (Hz)
3.2 explain and sketch the difference between longitudinal and transverse waves
Longitudinal waves oscillate parallel to the direction of travel
Transverse waves oscillate perpendicular to the direction of travel
3.3 Define amplitude, wavefront, frequency, wavelength and period of a wave and label them on appropriate diagram
Amplitude: maximum displacement of the wave (x axis to top of one wave)
Wavefront: A plane that joins points on adjacent waves together
Frequency: Number of complete waves that cross a point per second
Wavelength: Distance between adjacent peaks
Period of a wave: Time taken for one complete wave to pass a point
3.4 State what waves transfer and what they definitely don’t
Transfer: Energy and information
Don’t transfer: matter
3.5 Give the relationship between the speed, frequency and wavelength of a wave
Wave speed = Frequency x wavelength
v = f × λ
3.6 Give the relationship between frequency and time period:
Frequency = 1/time period F = 1/t
3.7 Write down the approximate speed of sound in air and electromagnetic waves in a vacuum in m/s
Sound = 340m/s
EM waves = 3.0x10^8 m/s
3.8 explain why there is a change in the observed frequency and wavelength of a wave when its source is moving relative to an observer, and give the name of this effect
Doppler effect
Wave speed is constant, so a moving source produces waves that are closer together in one direction and further apart in another. The wavelength is smaller and wave speed is the same. Since frequency = wave speed/wavelength, the frequency is greater
3.9 Name the 4 things that can happen to a wave when they interact with matter
Reflected, refracted, diffracted or absorbed
3.14 Are light waves transverse or longitudinal?
Transverse
3.14 State the two pieces of evidence that suggest light is a wave
It can be reflected and refracted
3.15 State the law of reflection
The angle of incidence equals the angle of reflection
3.16 Sketch a ray diagram showing refraction. Label the incident and refracted ray, the incident and refracted angle and the normal
JFDI
3.17 practical: Describe an experiment to investigate the refraction of light and explain the results. Do this using
rectangular blocks
Draw around the glass block, then direct a ray of light through it (at appx 40º)
Draw crosses to mark where the light enters and leaves the glass block. Join the crosses to create a line and attach these two lines.
Draw a normal at 90º and measure the angle of incidence and refracted angle using a protractor.
Calculate the RI using n = sin i/ sin r and repeat, taking averages.
Light refracts as different parts of it enter the glass and slow down.
3.17 practical: Describe an experiment to investigate the refraction of light and explain the results. Do this using
semi-circular blocks
Aim the light at the centre of the curved edge so that it leaves the centre of the flat edge of the semi circle (it enters along the normal and doesn’t refract)
Draw around the semi circle and mark the mid point. Then continue to increase the angle of incidence, until all of the light leaves at the surface of the flat side.
Draw crosses to mark this ray, and then connect this to the centre of the flat surface. Draw in a normal and measure this angle - it is the critical angle.
3.17 practical: Describe an experiment to investigate the refraction of light and explain the results. Do this using
triangular prisms
Shine white light through the prism until a spectrum of colours appears.
This happens as the different frequencies of light are refracted by different amounts (the higher it is, the more it is refracted)
Pneumonic for refraction?
FAST
Faster - Away from t˙he normal
Slower - Towards the normal
3.18 Write down the relationship between refractive index, angle of incidence and angle of refraction
n=sini/sinr
3.20 Describe what is needed for total internal reflection
Light enters at an incident angle higher than the critical angle
Light goes from a high refractive index to a low refractive index
3.20 Describe and explain the use of total internal reflection in transmitting information along optical fibres
Optical fibres are glass or plastic that have an inner core that has a higher refractive index than the rest of it.
Therefore, once light enters at the critical angle, it is always reflected and never leaves
3.20 Describe the role of total internal reflection in the use of triangular 90º prisms and where it can be used
If light enters one of the short sides at 90º it is TIR by the long side and leaves the other short side at 90º.
This can be used in a periscope or a camera
3.21 explain the meaning of critical angle c
If the incident angle is the critical angle, the refracted ray comes out along the surface
3.22 Write down the relationship between critical angle and refractive index
sinc=1/n
3.23 Is sound a longitudinal or transverse wave?
Longitudinal
3.23 State the two pieces of evidence that suggest sound is a wave
It can be reflected and refracted
3.24P State the frequency range for human hearing
20 - 20,000 Hz
3.25P practical: investigate the speed of sound in air
A holds a drum 200 metres away from B (measure using a trundle wheel)
B measures the time between seeing A strike the drum and when he hears it (using a stopwatch)
Repeat several times and take an average.
Work out speed by s=d/t
3.26P Describe how an oscilloscope displays a sound wave and sketch an example showing the time period and amplitude
The screen displaysa displacement time graph of the sound wave.
The amplitude shown represents the loudness of the sound
The horizontal axis can be used to work out the time period and then the frequency (f=1/t)
3.27P practical: Describe an experiment to investigate the frequency of a sound wave using an oscilloscope
Connect a microphone
Adjust the time setting so that at least one division is showed on the screen and read the time period.
Work out time period - wave speed x number of divisions one wave takes up.
1/t = f
3.28P Describe how the pitch of sound is represented by a wave
The pitch is represented by the frequency of vibration of the source
3.29P Describe how the loudness of a sound is represented by a wave
Loudness relates to the amplitude of vibration of the source
What is meant my critical angle?
The angle of incidence inside the glass (or whatever material) whereby TIR occurs
Explain the Doppler Effect
Frequency in front of direction of motion is smaller than that in the opposite direction.
This is because the emitter produces waves closer together.
Therefore, the wavelength is smaller, but the wave speed is the same - f=v/λ - f is higher
