Unit 4: Waves Flashcards
Do the booklet, and actually try to learn and do everything in it
What is the order of the EM spectrum (and give 1 use for each EM wave type)
jj
Why is it that when a light ray enters a semi circle from the curved part it wont change direction in the semi circle
It is because the light ray that comes into contact will always be at a 90 degree angle to the edge.
- This is because the light ray going towards the centre of the circle is a radius, and from circle theorems we know that the radius always meets a tangent at 90 degrees
- This then implies that the ray is at a 90 degree angle to the tangent at that point
- Meaning that the ray line is the exact same as the normal line (since the definition of a normal line is literally the line perpendicular to the tangent at the point of tangency)
- Meaning the angle of incident is 0
- So the ray doesnt refract
What is the order of the wavelength of colours/visible light?
For reference: Red has the longest wavelength, violet has the shortest
Can there be total internal reflection when a ray enters glass from air
No - because glass has a higher refractive index/is more dense
What creates/causes the visible light to become a spectrum
Dispersion
Why cant dispersion occur in a rectangular box like it does in a triangular prism?
Because there are 2 parallel surfaces, the two refraction affects at the two parallel interfaces cancel each other out
With concave lenses the image produced is always ______
Virtual
When learning about ray diagrams you NEED to watch these two videos in the order they are listed in
- https://www.youtube.com/watch?v=807YLUlOHh0
- https://www.youtube.com/watch?v=JNp_-00-fxU&t=202s
Do the quizlet/summary sheets/PPQs on the last slide
https://docs.google.com/presentation/d/1yqPbnwdtefD6dkI4tayjOtoUyk-9fSb7qHvWGArJTI0/edit#slide=id.g468874d7ed_0_6
What is the law of reflection
Angle of incidence = Angle of reflection, or I = R
Comparing image reflected in a plane mirror to an object
- Same size
- Same distance behind the mirror as the object is in front of it
- Left-right inverted
- Virtual
Define real image
A real image is an image that can be projected onto a screen. Rays of light actually pass through the image.
Define virtual image
A virtual image cannot be projected onto a screen. It appears to come from behind the lens and can only be seen by looking through the lens.
Define refraction
The change in direction of a wave passing from one medium to another caused by its change in speed. For example, waves travel faster in deep water than in shallow.
Why is light that enters through a window not distorted (hence we get to actually see the world outside)
When we look at the world through a window, we are looking through a parallel sided sheet of glass. We do not see a distorted image because, although the rays of light are shifted slightly as they pass through the glass, they all reach us travelling in their original direction.
Why do we see a distorted view when we look through a window that is covered with raindrops?
Every raindrop on the windshield act as a convex lens that distorts the background image that surrounds this drop.
What is the refractive index?
The amount by which the speed of light is slowed down, e.g. is the speed of light is halved when travelling through a certain material then it means that the refractive index of that material is 2.
Note that speed of light = speed of light in a vaccum
Does refractive index have any units?
NOPE
What are waves in physics?
Physicists use waves as a model to explain the behaviour of light, sound, and other phenomenon.
A wave transfers energy without ______ being transferred
matter
On the graph of a longitudinal wave, which parts represent compressions and which parts represent ra-refractions
Describe the motion of molecules of water as a ripple moves across the surface of water in a ripple tank
They actually move up and down. When they move up, they drag the other molecules next to them up – then they move down, dragging the molecules next to them down too. That’s what creates the peaks and troughs you see on the surface of the water.
What is 1 Hz (Note: Hz is a measurement of frequency)
1 Hz = 1 wave per second
What is diffraction?
Image result for define diffraction light
Diffraction of light is defined as the bending of light around corners such that it spreads out and illuminates areas where a shadow is expected. Waves are diffracted most when the width of the gap/alleyway are the same as the wavelength of the waves.
Examples of longitudinal waves
Sound waves
P-waves (a type of seismic wave)
Pressure waves caused by repeated movements in a liquid or gas
Theres a cognito video on the p-waves thingy
Longitudinal waves can be seen in a _____(insert common practical here)______
Slinky:
What are the medical uses of optical fibres? (in textbook)
Optical fibres are also used in medicine. An endoscope is a device that can be used to look inside a patients body - for example, to see the stomach. One bundle of fibres carries light down into the body (it is dark in there), while another bundle carries an image back up to the user.
What is meant by wave motion?
Wave motion is the transfer of energy from one point to another. We can demonstrate this by hanging an object on a stretched string and then sending a pulse down the string (by moving it up and down quickly like a wave).
Define frequency
The amount of waves passing a particular point per second
Define wave speed
The distance covered by a wave per second
Define wavelength
The distance between a point on one wave and the same point on another wave
Define wavelength
The distance between a point on one wave and the same point on another wave
Define amplitude
The distance from the equilibrium position to the maximum displacement
Very good summary notes: https://issr.edu.kh/science/CIE/0625%20iGCSE%20Physics/Summary%20Notes/0625%20CIE%20iGCSE%20-%203%20Waves%20-%20Summary%20Notes.pdf
What is a wavefront?
Waves transfer energy and information without transferring matter. The wavefront is the front of the wave, or the same point on each wave. Generally speaking this tends to be the crest or peak of the wave.
Period vs wavelength
The difference is reflected in the horizontal axis in each plot: wavelength is a displacement in space, and period is a displacement in time
The period of a wave is how long it takes for one wave to go past a certain point/ you can think of it as the time it takes one oscillation to complete.
Transverse waves
- Has peaks/crests and troughs
- Oscillations/vibrations are perpendicular to the direction of energy transfer
- Examples include EM waves and ripples on water
Longitudinal waves
- Consists of compressions (particles move together) and rarefactions (particles move apart)
- Oscillations/vibrations are parallel to the direction of the transfer of energy
- Examples include sound waves and seismic p waves
Describe diffraction
When waves meet a gap in a barrier, they carry on through the gap. However, the waves spread out to some extent into the area beyond the gap. This is diffraction. The extent of the spreading depends on how the width of the gap compares to the wavelength of the waves.
Define refractive index
a measure of how much the speed of a wave changes compared to the speed in a reference medium i.e. air or a vacuum.
Define critical angle
The angle of incidence when the angle of refraction is 90 degrees, and beyond which will cause total internal reflection rather than refraction
What is the order of the EM spectrum?
- Radio waves
- Microwaves
- Infrared
- Visible light (red, orange, yellow, green, blue, indigo, violet)
- Ultraviolet
- X-rays
- Gamma rays
Provide examples of each wave form on the EM spectrum (IGCSE statement so you actually have to remember these exact examples)
Radio waves: Radio and television communications
Microwaves: Satellite television and telephone communications
Infrared: Electronic devices (toasters), remote controls for TVs, Intruder alarms
Visible light: Photographs, optical fibres
Ultraviolet: disinfect water
X-ray: Medicine (scan fractures), Security (scan baggage for e.g. explosives)
Gamma rays: Radio therapy (kill cancerous cells), Sterilize medical equipment
What is the speed of electromagnetic waves in a vacuum?
3 x 10^8 m/s (metre/second)
Demonstrate an understanding of safety issues regarding the use of microwaves and x-rays
Both can kill cells in the body when used: microwaves heat up the water molecules in skin cells causing them to die; while x-rays ionize cells causing possible deadly mutations.
State the dangers of ultraviolet radiation, from the Sun or from tanning lamps.
ultraviolet can damage skin cells and lead to skin cancer and damage the eyes, it can cause skin to age prematurely
State that the approximate range of audible frequencies for a healthy human ear
20 Hz to 20 000 Hz
Amplitude affects _______ of sound.
Frequency affects the ______ of sound.
Volume
Pitch
Describe and interpret an experiment to determine the speed of sound in air, including calculation.
You have to use a fast timer and microphones (from the booklet).
(do NOT do this one) Clap far away from the wall until you hear the echo. Calculate the speed of the sound using this. Note that you should stand far from the wall since if you stand too close humans wouldn’t be able to differentiate between the original sound and the echo.
What are the three properties of electromagnetic waves?
- They’re all transverse
- All can travel through a vacuum
- They all travel at the same speed in a vacuum
Infrasound can be used to monitor…
Earthquakes and volcanoes. Infrasound can be used to investigate the internal structure of our planet, just like ultrasound is used for foetal scanning. Earthquakes produce very powerful seismic waves that can be classed as infrasound waves. Seismic waves from large earthquakes are detected around the world.
Uses of ultrasound include
Uses of ultrasound include:
breaking kidney stones.
cleaning jewellery.
foetal scanning.
detecting cracks in machinery.
Past paper questions
https://igcseexamguru.com/pastpapers/Topical%20Past%20Papers/Physics/IGCSE%20Topical%20Past%20Papers%20Physics%20P4%20C9%20-%20C10.pdf
define compression and rarefaction in a longitudinal wave
compressions are regions of high pressure due to particles being close together. rarefactions are regions of low pressure due to particles being spread further apart.
