unit 3 - waves Flashcards
Waves
disturbances created in a medium which transfers energy and momentum from one point to another, cant tranfer matter
In waves, what do particles do>
They dont move, they just oscillate and vibrate , tranansferring the wave from one particle to another, and sometimes get reflected
what happens to medium in waves
remains static
Types of waves based on requirement of meidum to travel
Electromagnetic and Mechnical waves
Electromagnetic waves
Waves which do not require a medium to propoagte. Wave in which the electrical field and the magnetic field mutually oscillate perpendicular to the propagation of the wave\
Eg = Light waves
Mechanical waves
Waves which require medium to travel
eg = Sound waves, water ripples, seismic waves
Types of waves based on movement of particles
Transverse and Longitudinal
Transverse waves
Propogation of particle is perpendicular to the direction of propogation of energy, particles oscillate up and down
eg = em waves and light waves
Longitudanal Waves
- Vibration of particles in the medium is parallel to the direction of propagation of wave
It looks likes particles are moving left to right but they come back to their mean position
Eg - sound waves, waves produced in a slinky
Compression
Area in longitudnal waves where the particles are close to each other, the area where density and pressure are higher than normal
Rarefaction
Area in a longitudnal wave where the particle are far apart from each other, the area where density and pressure are less than normal
4 characterstic properties of waves
- wavelength
- amplitude
- frequency
- Wave velocity
Wavelength (transverse)
Distance between two consecutive troughs or crests
Si unit = mtr
Symbol = Lambda
wavelength (longitudanal)
measure distance between 2 consecutie compressions or rarefaction
Amplitude
Maximum displacement of a particle from its mean position in the positive or negative direction
si unit = mtr
symbol = A
Frequency and how to calculate it from diagram
- No. of disturbances/waves per unit time
- No. of oscillations per unit time
- Si unit = Hertz (Hz)
- 1 Hz = 1 wave per second
- To calculate frequency, we can also count the number of waves (from crest to crest or trough to trough) in a one second diagram
Wave velocity with formula
- distance a wave travels per unit of time
- Also known as Phase velocity
- Symbol = V
- Si unit = ms^-1
formula = lambda times frequency
Time period, si unit and formula
Time taken to complete one full oscillation
Si unit = sec
formula = T = 1/f
Wave equation
Speed = Freuqney times wavelength
Frequency = speed/wavelength
Wavelength = speed/frequency
Ray
direction in which a wave propogates
reflection
A phenomenon in which a wave bounces back into the same medium after being incident on a reflection surface
laws of relfection
- The incident ray, the reflection ray and the normal to the reflecting surface must lie on the same plane
- The angle of incidence must be equal to the angle of reflection
Refraction
- For refraction, the wave must travel must rarer to denser medium
Change in speed of a wave when passing from one medium to another
- Change in direction of motion
- Frequency does not change!
- Angel of incidence increases = Angle of refraction also increase
bending of refracting ray - denser to rarer
Away from normal
Bending of refracting rray - rarer to denser
towards the normal
Laws of refraction
- The incident ray, the refracting ray and the normal to the surface or separation at the point of incidence must lie on the same plane
- Snells Law: The ratio of sine of angle of incidence and the sine of angle of refraction for a given pair of media is always constant and is called the refractive index of the second medium with respect to the first medium
formula for snells law
sin i/ sin r = n2/n1 = v1/v2
Total internal reflection
- when a wave propogates from a denser to rarer medium, TIR (total internal reflection) takes place
- Speed increase in TIR
- Refracted ray bends away from normal
- In TIR, 100% of the wave is reflected
conditions for total internal relfection
- Incident ray must travel from denser to rarer medium
- ∠i must be greater than the critical angle
critical angle
Angle of incidence for which the corresponding angle of refraction is 90°
diffraction
Phenomenon in which a wave spreads whenever it comes across an obstacle or a slit, provided the size of the slit or the obstacle in comparable to the wavelength of the wave
dispersion
- Phenomenon in which a polychromatic light splits into its monochromatic constituents
Higher the wavelength, lesser the deviation
eg = white light splitting into vibgyor colour
basic cause of dispersion
refraction multiple times
electromagnetic spectrum (decreasing order of wavelength)
Radio waves
Micro waves
Infra red radiation
Visible light spectrum
Ultra violet rays
X rays
Gamma radiation
Infra red radiatiom
Electromagnetic radiation which gives us the feeling of warmth. Any value above absolute 0 (O kelvin) will give IRR
How the wavelength of Infra red radiations determined
by temperature and doesnt have one set value
why is there no unit for refractive index
ratio of sines of 2 speeds and since sines have no unit, this also doesnt have any unit
sound waves
- Type of mechanical wave
- Type of longitudanal wave
- They can be described as patterns/sequence of disturbance created in space-time which compress and expand the air around it to create disturbances which are known as sounds
what is pitch in sound waves
Frequency of sound waves
Higher frequency = higher pitch
What happens in Echo location (specifically for bats)
Animals like bats scream high frequency sounds and these waves reflect of animals, objects and low pressure regions and then using a bats sense of sound, he is able to use these reflection to paint a picture of his surroundings and find out the exact speed, size, direction, and location of these objects
Where is echo location used by humans
In SONAR and radar systems
Absorption in waves
When a wave transfers its energy onto a material it passes through, causing the material’s atom and molecules to vibrate
Pneumonic to memorise electromagnetic spectrum decreasing order or wavelengths
Ranbir Mohan Is Very Ultra eXtraordinary Guy
Sound waves travel best through which medium
Best travel trhough solids due to prescene of closely packed molecules, whcih allows for faster Kinetic energy transfer between molecuulesm and hence they travel faster through solids quickly
However, they can also travel thorugh fluids
Relationship between wavelength, energy and frequnecy as one increases
Higher wavelength = Lower frequency = Low energy
Lower wavelength = Higher frequency = Higher energy
Visible Light spectrum in order of highes to lowest wavlenegth
Red (highest wavelength, lwoest freuqnecy)
Orange
Yellow
Green
Blue
Indigo
Violet (lowest wavelength, hgihest frequency)
Why does Red appear at the top of diffraction and violet at the point
- Red has lowest frequency, whereas violet has the highest frequency
- Red refracts the lowest
- Red is refracted the least
Application of each EM wave and reason
- Radio Waves - Used for long distance communication as they can reflected from the Earth’s surface
- Mircowavesused for Sattelite communicaton because they can penetrate earth’s atmosphere
- Infrared - Optical fibre communication, Because they can undergo total undergo total internal reflection
- Visible Light - Taking photos as cameras can detetct visible light
- UltraViolet - Detecting security ink as its fluroses with UV lighitng
- X ray - Medical imaging as it can pass through tissues but not bones
- Gamma used to clean medical tools as itcan kill cells and bacteria
