4th - Light And Sound Flashcards
What are light waves
Can they be reflected and refracted
Transverse
Yes
What are sound waves
Can they be reflected And refracted
Longitudinal
Yes
Law of reflection
Angle of incidence = angle of reflection
Definition of a transverse wave
Oscillations are perpendicular to direction of energy transfer
Definition of a longitudinal wave
Oscillations are parallel to direction of energy transfer
What is refraction
Wave changing direction when it moves from one material to another
Due to the wave changing speed
What happens to light when it enters a more dense material
Slows down
Turns towards the normal
What happens to light when it enters a less dense material
Speeds up
Turns away from the normal
Equation for refractive index
N = sin ( i ) / sin ( r )
(N = refractive index)
- Practical
How to investigate refractive index
- mark where ray enters glass block ( draw normal line at 90 degrees to surface)
- measure angle of incidence (protractor)
- mark exit point of ray -> show refracted ray
- measure angle of refraction (protractor)
- vary angle of incidence + measure angle of refraction
- repeat + take average
- plot graph of sin ( i) against sin (r)
- refractive index = gradient
What does it mean when ray refracts at 90 degrees to normal
Angle of incidence = critical angle
What does the ray undergo when
Angle of incidence > critical angle
Total internal reflection
Equation to find critical angle
Sin ( c ) = 1 / n
What is total internal reflection used for
In optical fibres to carry data
What are optical fibres made of
Plastic or glass
What does optical fibres have
Outer cladding - that has a lower refractive index than the inner core
What does light do in an optical fibre
Totally internally reflect
Light will always hit a boundary at a value higher than c
What happens to light in a right angled prism
Totally internally reflected
Frequency range from human hearing
20 - 20,000 Hz
What are frequencies greater than 20,000 Hz called
Ultrasound
What are frequencies less than 20 Hz called
Infrasound
What does higher frequency vibrations detected as
High pitch sounds
What are higher amplitude vibrations detected as
High volume sounds
*practical
Investigate speed of sound in air by clapping
- speed = distance / time
- measure at least 100m using trundle wheel
- one person holds stopwatch, other person claps
- measure time taken between seeing clap and hearing clap
- repeat and take average
- use equation
*practical
Investigate speed of sound in air using a pair of microphones
- speed = distance / time
- measure at least 1m between two mics (meter rule)
- hit a metal plate with a hammer next to mic A
- measure time taken between mic A and B detecting sound (electronic timer)
- repeat and average
- equation
What do oscilloscopes display sound waves as
A trace on a screen
What do microphones convert travelling sound waves to
Electrical signals
X and y axis on an oscilloscope
X - time
Y- amplitude
How to find the frequency of a wave using an oscilloscope
- connect oscilloscope to microphone - get a steady trace
- get a minimum of 1 complete cycle on screen
- count number of squares for 1 complete cycle
- multiply no. Of squares by time base = time period
- frequency = 1 / time period
