Waves ( light and sound) Flashcards
Topic 2 D
light waves are what type of waves
transverse waves
can light waves be refracted
yes
can light waves be reflected
yes
what is the law of reflection
angle of incidence = angle of reflection
properties of mirror images (4)
- upright
- same size as objects
- laterally inverted
- virtual ( can’t be projected on a screen)
frequency range for humans
20 - 20000 Hz
sound waves are what type of wave
longitudinal
reflection of a sound wave is called an
echo
sound can undergo
reflection and refraction
what waves can be reflected or refracted
all waves
reflection happens when
A wave hits a boundary between two media and does not pass through, but instead stays in the original medium
refraction happens when
A wave passes a boundary between two different transparent media and undergoes a change in direction
An incident ray has an arrow pointing towards or away from the boundary ?
towards
A reflected ray has an arrow pointing towards or away from the boundary?
away
The change in direction of the refracted ray depends on the difference in ____ between the 2 mediums
density
in refraction, From less dense to more dense (e.g air to glass), light bends to/away the normal
towards
in refraction, From more dense to less dense (e.g. glass to air), light bends away/to from the normal
away
When passing along the normal (perpendicular) the light does or doesn’t bend
doesn’t
When light passes into a denser substance the rays will slow down, so rays will bend towards/away normal
towards
The only properties that change during refraction are (2)
speed and wavelength
does frequency change during refraction
no
does light change colour when it refracts
no
INVESTIGATION REFRACTION PRACTICAL
Place the glass block on a sheet of paper, and carefully draw around the rectangular perspex block using a pencil
Switch on the ray box and direct a beam of light at the side face of the block
Mark on the paper:
A point on the ray close to the ray box
The point where the ray enters the block
The point where the ray exits the block
A point on the exit light ray which is a distance of about 5 cm away from the block
Draw a dashed line normal (at right angles) to the outline of the block where the points are
Remove the block and join the points marked with three straight lines
Replace the block within its outline and repeat the above process for a ray striking the block at a different angle
Repeat the procedure for each shape of perspex block (prism and semi-circular)
what is snells law
n = sin i
——
sin r
what is n, i and r in snells law
n = the refractive index of the material
i = angle of incidence of the light (°)
r = angle of refraction of the light (°)
what is the refractive index
a number that is always larger than 1 and is different for different materials
Objects which are more optically dense have a ___ refractive index
higher
Objects which are less optically dense have a ___ refractive index,
lower
INVESTIGATING SNELLS LAW PRACTICAL ( aim and method)
AIM - To investigate the refractive index of glass, using a glass block
Place the glass block on a sheet of paper, and carefully draw around the block using a pencil
Draw a dashed line normal (at right angles) to the outline of the block
Use a protractor to measure the angles of incidence to be studied and mark these lines on the paper
Switch on the ray box and direct a beam of light at the side face of the block at the first angle to be investigated
Mark on the paper:
A point on the ray close to the ray box
The point where the ray enters the block
The point where the ray exits the block
A point on the exit light ray which is a distance of about 5 cm away from the block
Remove the block and join the points marked with three straight lines
Replace the block within its outline and repeat the above process for a rays striking the block at the next angle
what does the refractive index measure
how much light will ‘bend’ when passing through a substance.
what is the critical angle
angle of incidence that gives an angle of refraction of 90º
total internal reflection happens when
light travels from a more dense medium to a less dense medium at an angle bigger than the critical angle
2 conditions for total internal reflection are
The angle of incidence > the critical angle
The incident material is denser than the second material
total internal reflection is used in (2)
optical fibres and prisms
Total internal reflection is used to reflect light along optical fibres, meaning they can be used for (3)
communications
endoscopes
decorative lamps
Prisms are used in a variety of optical instruments, including (4)
periscopes
binoculars
telescopes
cameras
when light travels through a periscope, does it totally internally reflect and what does this cause
yes and it causes the light to reflect at right angles
in total internal reflection, is all the light reflected ?
yes
As the angle of incidence increases it will eventually surplus the ____ and lead to ____
critical angle
total internal reflection
Equation between critical angle and refractive index
sin c = 1
—-
n
the larger the refractive index of a material, the ___ the critical angle
smaller
Light rays inside a material with a high refractive index are ___ likely to be totally internally reflected
more
INVESTIGATING THE SPEED OF SOUND IN AIR ( without oscilloscope)
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
then use equation spped = distance /time to figure speed of sound
INVESTIGATING SPEED OF SOUND USING OSCILLOSCOPE
Connect two microphones to an oscilloscope
Place them about 2 m apart using a tape measure to measure the distance between them
Set up the oscilloscope so that it triggers when the first microphone detects a sound, and adjust the time base so that the sound arriving at both microphones can be seen on the screen
Make a large clap using the two wooden blocks next to the first microphone
Use the oscilloscope to determine the time at which the clap reaches each microphone and the time difference between them
Repeat this experiment for several distances, e.g. 2 m, 2.5 m, 3 m, 3.5 m
speed of sound found out using equation
An oscilloscope is a device that
can be used to study a rapidly changing signal, such as:
A sound wave
An alternating current
An oscilloscope is used to display sound as
a waveform
When a microphone is connected to an oscilloscope, how is the wave displayed on the screen
as a transverse wave
the x-axis shows what on an oscilloscope
the time base
INVESTIGATING FREQUENCY OF SOUND USING OSCILLOSCOPE PRACTICAL
Connect the microphone to the oscilloscope
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
If the frequency of vibration is high, the sound wave has a __ pitch
HIGH
If the frequency of vibration is low, the sound wave has a ___ pitch
LOW
The pitch of a sound is related to the ___ of the vibrating source of sound waves
Frequency
The loudness of a sound is related to the ___ of the vibrating source of sound waves
amplitude
If the sound is loud, the sound wave has a ___ amplitude
large
