Properties of waves, including light and sound Flashcards
What do waves transfer?
Energy
Waves transfer energy without transferring what?
Matter
Describe wave motion
- No matter travels with waves as it travels between 2 points
- Points on the wave vibrate back and forth about a fixed point
What is a wavefront?
A way of viewing waves from above
What is meant by the speed of a wave?
The distance travelled by a wave per second
What is meant by the frequency of a wave?
Number of waves passing any point per second
What is the SI unit for frequency?
Hertz (Hz)
What is the formula for frequency?
f= 1/period
What is meant by period?
Time taken for 1 oscillation
What is the SI unit for period?
Seconds (s)
What is meant by the term wavelength?
Distance from a point on one wave to the same point on the next wave
What is the SI unit for wavelength?
Metres (m)
What is the formula for speed?
v = fλ
What is meant by the term amplitude?
The height of a wave measured from the middle of the wave
What is a transverse wave?
Waves in which oscillations are perpendicular to direction of travel
What is a longitudinal wave?
Waves in which oscillations are parallel to direction of travel
What are 2 differences between transverse and longitudinal waves?
- Oscillations and direction of travel
2. Transverse waves have peaks and troughs and longitudinal waves have compressions and rarefactions
What are 3 wave effects?
- Reflection
- Refraction
- Diffraction
What is reflection?
The bouncing back of a wave
What is refraction?
The change in speed of a wave when it passes from one medium to another
What is diffraction?
The spreading of a wave
What are the laws of reflection?
- Angle of incidence = angle of reflection
2. The incident ray, reflected ray and the normal all lie in the same plane
What are the effects on speed, frequency and wavelength of a wave that is reflected?
No effect
What are 3 effects of refraction of a wave into a different medium?
- Change in speed
- Change in wavelength
- Change in direction
What is the effect on a wave travelling from a more dense medium to a less dense medium?
- Speed decreases
- Wavelength decreases
- Bends away the normal
What is the effect on a wave travelling from a less dense medium to a more dense medium?
- Speed increases
- Wavelength increases
- Bends towards from the normal
Which property of a wave is not affected by refraction?
Frequency
Is shallow water less dense or more dense than deep water?
Less dense
What are 2 factors that influence diffraction?
- Size of the gap
2. Wavelength
How does the size of a gap affect diffraction?
Wider gaps produce less diffraction
How does wavelength affect diffraction?
Greater wavelength produces more diffraction
What 3 properties are not affected by wavelength?
- Speed
- Wavelength
- Frequency
What are 3 characteristics of an optical image formed by a plane mirror?
- Same size as the object
- Same distance behind the mirror as the object is in front of it
- It is directly in line with the object
Is the image in a plane mirror virtual or real?
Virtual
Exam tip ; )
When drawing light waves being reflected take care to get the angle about right.
If they are slightly out it won’t be a problem, but if there is an obvious difference between the angle of incidence and the angle of reflection then you will probably lose a mark.
Describe an experimental demonstration of the refraction of light
- Place the glass block on plain paper and draw around the block using a pencil
- Use a ray box to project a single ray of light towards the glass block
- Using a pencil, mark the points before it reaches the glass block and where it hits the glass block
- Mark the points where it leaves the glass block and after it has left the glass block
- Connect the points using a ruler and pencil
- Repeat the process with the ray striking the block at different angles
- Use Snell’s Law
What is Snell’s Law?
As light travels from a less dense medium to a more dense medium it slows down and bends towards the normal
What is refractive index?
Degree at which light is bent by the second medium
What is the relationship between angle of incidence and angle of refraction given by Snell’s Law?
n = sin i ÷ sin r
What is the formula for refractive index?
n = speed of light in vacuum ÷ speed of light in medium
What is critical angle?
- Angle of incidence that gives an angle of refraction of 90°
- Light travels from a more dense medium to a less dense medium
What is the formula for critical angle?
n = 1 ÷ sin c
Describe internal reflection
- Light travels from a more dense to a less dense medium
- Most of the light is refracted
- A small amount is reflected
Describe total internal reflection
- Light travels from a more dense to a less dense medium
- Angle of incidence is greater than the critical angle
- All of the light is reflected
What are 2 conditions for total internal reflection?
- Light must be travelling from a more dense to a less dense medium
- Angle of incidence must be greater than the critical angle
Describe and explain the action of optical fibres particularly in medicine and communications technology
- Total internal reflection is used to reflect light along optical fibres
- This allows the transmission of high speed internet
Describe and explain the action of optical fibres particularly in medicine and communications technology
- Total internal reflection is used to reflect light along optical fibres
- This allows the transmission of data at high speeds on the internet
- Optical fibres are used in medicine in order to see within the human body
Exam tip ; )
When drawing light reflecting down an optical fibre, make sure that each time it reflects the angle of reflection is equal to the angle of incidence.
What is the principal focus?
Point where rays parallel to the lens focus
What is the focal length?
The distance of the principal focus from the lens
What is the optical centre?
The centre of the lens
What is the principal axis?
Line that goes through the optical centre
What image will form if the object is between the centre and the focal length?
- Virtual
- Enlarged
- Upright
What image will form if the object is between the focal length and twice the focal length?
- Real
- Enlarged
- Inverted
What image will form if the object is placed exactly on twice the focal length?
- Real
- Same size
- Inverted
What image will form if the object is beyond twice the focal length?
- Real
- Diminished
- Inverted
Are real or virtual images projected onto a screen?
Real images
Describe the use of a single lens as a magnifying glass
The lens should always be held close to the object
What is a real image?
An image formed by the convergence of light rays
What is a virtual image?
An image formed when the rays appear to come from behind the lens
What is a converging lens also know as?
Convex lens
What is a use of dispersion of light?
Separating white light
How many colours are there in the spectrum of light?
Seven
What are the 7 colours in the spectrum of light?
ROY G BIV
Which of the 7 colours of light has the greatest wavelength?
Red
Which of the 7 colours of light has the smallest wavelength?
Violet
What causes the colours of light to bend by different amounts?
They slow down by different amounts
What is the relationship between wavelength and speed in prism?
The greater the wavelength, the slower the speed
What is light of a single wavelength or single frequency known as?
Monochromatic
What are the main features of the electromagnetic spectrum?
- Radio waves
- Microwaves
- Infrared
- Visible light
- Ultraviolet
- X-rays
- Gamma rays
What mnemonic is used to list the features of the electromagnetic spectrum?
Roman Men Invented Very Useless X-ray Guns
Which of the 7 features of the electromagnetic spectrum has the greatest wavelength?
Radio waves
Which of the 7 features of the electromagnetic spectrum has the shortest wavelength?
Gamma rays
What is the speed of electromagnetic waves in a vacuum?
3.0 × 10^8
What are radio waves used for?
Radio and television communications
What are microwaves used for?
Satellite television and telephones
What is infrared used for?
- Electrical appliances
- Remote controllers for television
- Intruder alarms
What are X-rays used for?
Medicine and security
What are the dangers of microwaves?
High levels of microwaves cause heating of internal organs
What are the dangers of X-rays?
Can harm cells and cause cancer
Why are high levels of microwaves dangerous?
Water molecules absorb microwaves strongly
Why are X-rays dangerous?
They are highly ionising
How are sound waves produced?
Vibrating sources
What type of wave are sound waves?
Longitudinal
What is a compression?
Space where molecules are bunched together
What is a rarefaction?
Space where molecules are spaced out
What is the approximate range of audible frequencies for a healthy human ear?
20 Hz - 20,000 Hz
What is ultrasound?
Sound waves with a frequency greater than 20,000 Hz
What is needed to transmit sound waves?
A medium
Describe an experiment to determine the speed of sound in air
- Two observers are set apart at a known distance
- Observer A fires a gun
- Observer B starts the stopwatch when he sees the puff of smoke
- Observer B stops the stopwatch when he hears the sound
- Use the formula speed = distance ÷ time
- Observers switch position and repeat the experiment
- Values are averaged to obtain speed of sound
What is the speed of sound in gases?
330 m/s
What is the speed of sound in liquids?
1,500 m/s
What is the speed of sound in solids?
5,000 m/s
Which property of a sound wave is related to loudness?
Amplitude
Which property of a sound wave is related to pitch?
Frequency
How amplitude affect loudness?
Greater amplitude results in greater loudness
How frequency affect pitch?
Greater frequency results in higher pitch
What is an echo?
Reflection of a sound wave
