Waves & Particle Nature of Light (5) Flashcards
What generates waves?
Oscillating sources generate waves that travel away from the source.
What is the definition of wavelength (λ)?
The distance between a point on a wave and the same point on the next cycle (e.g., crest to crest).
What is amplitude (A)?
The maximum displacement from the equilibrium position
What is period (T)?
The time taken for one complete oscillation at a point on the wave.
What is frequency (f)?
The number of complete wave cycles per second, measured in Hertz (Hz).
What is wave speed (c)?
The rate at which a wave moves through a medium.
What type of graph represents a wave’s displacement?
A sinusoidal graph shows amplitude and wavelength.
How do you determine amplitude from a graph?
Measure the maximum displacement from the equilibrium position.
What is the wave speed equation
v=fλ
How does wavelength affect frequency at constant wave speed?
If wavelength increases, frequency decreases, and vice versa.
What units are used for the wave equation variables?
Velocity (m/s), wavelength (m), frequency (Hz).
What prefix is used for nanometres and megahertz?
nm = 1e-9m
MHz=1e6Hz
What is a longitudinal wave?
A wave where particles oscillate parallel to the direction of propagation.
What are compressions in a longitudinal wave?
Regions of high pressure where particles are close together.
What are rarefactions?
Regions of low pressure where particles are spread apart.
Give three examples of longitudinal waves.
Sound waves, ultrasound waves, and P-waves from earthquakes.
Can longitudinal waves be polarized?
No, only transverse waves can be polarized.
How is wavelength measured in a longitudinal wave?
The distance between two consecutive compressions or rarefactions.
What should you check in wave-related exam questions?
Whether the wave travels parallel (longitudinal) or perpendicular (transverse)
What determines the speed of sound in different materials?
The density and elasticity of the medium.
What is a transverse wave?
A wave where particles oscillate perpendicular to the direction of propagation.
What are crests and troughs?
Crests are wave peaks; troughs are the lowest points.
Give three examples of transverse waves.
Electromagnetic waves, waves on a rope, vibrations on a guitar string.
Can transverse waves be polarized?
Yes, they can be polarized.
What determines the energy of a transverse wave?
The amplitude.
What is the difference between transverse and longitudinal waves?
Transverse waves oscillate perpendicular, while longitudinal waves oscillate parallel.
What happens when transverse waves interfere?
Constructive or destructive interference occurs.
What property of light makes sunglasses effective?
Polarization.
What are the two common graphs used to represent transverse waves?
Displacement vs. distance and displacement vs. time graphs.
How does a displacement vs. distance graph differ from a displacement vs. time graph?
Displacement-distance shows a snapshot of the wave’s shape, while displacement-time shows how a point moves over time.
How can compressions and rarefactions be represented on a longitudinal wave graph?
Compressions appear as peaks (high pressure), and rarefactions appear as troughs (low pressure).
What happens when a stationary wave is plotted on a graph?
It shows nodes (points of no displacement) and antinodes (points of maximum displacement).
What is intensity in terms of waves?
Intensity is the power per unit area of a wave.
What happens to intensity when amplitude doubles?
Intensity increases by a factor of 4.
What is the relationship between intensity and frequency?
Intensity is proportional to the square of frequency.
What is a spherical wave
A wave that spreads equally in all directions from a point source.
What is the inverse square law?
Intensity decreases with the square of the distance from the source.
What happens to intensity if distance doubles?
Intensity is reduced by a factor of 4
Why does intensity decrease with distance?
Energy spreads over a larger area.
What is the unit of intensity?
Watts per square meter (W/m²).
How does a progressive wave transfer energy?
Through oscillations without transporting matter.
What is an example of a spherical wave?
Light from a bulb or sound from a speaker.
What is refraction?
A change in speed of light due to different optical densities.
What happens when light enters a denser medium?
It slows down and bends toward the normal.
What happens when light enters a less dense medium?
It speeds up and bends away from the normal.
What is the refractive index?
A measure of how much light slows down in a medium.
What is the refractive index of a vacuum?
1 (the highest speed of light).
Why does light not refract when passing along the normal?
There is no change in direction, only in speed.
What does a higher refractive index indicate?
Slower light speed and greater bending.
What is the approximate refractive index of air?
1
What is the refractive index of water
1.333
What is the refractive index of glass
1.5
What is the critical angle? (2)
- The angle of incidence where the refracted ray travels along the boundary.
- The angle above which total internal inflection occurs
What happens when the angle of incidence exceeds the critical angle?
Total internal reflection occurs.
What two conditions are needed for total internal reflection?
Light must travel from a denser to a less dense medium, and the angle must be greater than the critical angle.
How do you calculate the critical angle?
SinC=n2/n1
What happens if light moves from a less dense to a more dense medium at an angle greater than the critical angle?
It refracts, not reflects.
What happens when the critical angle is reached?
The refracted ray travels along the boundary.
How does increasing the refractive index affect the critical angle?
It decreases the critical angle
Why does total internal reflection not occur in water-to-glass transmission?
Because light moves into a denser medium.
What conditions are necessary for TIR?
Light must be in a denser medium and hit at an angle greater than the critical angle.
What happens to light during TIR?
It reflects instead of refracting.
How do optical fibers use TIR?
Light bounces along the fiber without escaping
What is the advantage of TIR in fiber optics
Minimal energy loss and fast signal transmission
What role does the refractive index play in TIR?
A higher index reduces the critical angle, making TIR more likely.
How does TIR create a mirage?
Hot air causes light to bend, making the sky appear reflected.
How do diamond’s optical properties enhance sparkle?
A high refractive index leads to a small critical angle and more internal reflections.
Why doesn’t TIR occur when light moves from air to water?
Light is entering a denser medium, so it refracts instead.
What are the two types of lenses?
Convex (converging) and concave (diverging)
What is a convex lens?
A lens that brings parallel rays to a focus.
What is the principal focus of a convex lens?
The point where refracted rays converge.
What is the focal point also called
Principle focus
What determines the focal length of a convex lens
The curvature of the lens.
What is a concave lens?
A lens that causes light rays to spread out.
What is another name for a convex lens?
A converging lens
What is another name for a concave lens?
A diverging lens.
What type of images do concave (diverging) lenses produce?
Virtual, diminished, and upright images.
How do convex (converging) lenses affect light?
They focus light to form real or virtual images.
What is an example of a convex lens that produces virtual images
A magnifying glass
What is a virtual image (2)
An image that can’t be projected onto a screen
An image where the rays don’t actually meet
What is a real image (2)
An image that can be projected onto a screen
An image where the rays meet to produce the image
What are the three ways to describe an image?
Real/virtual, size compared to object, and orientation.
What happens if an object is beyond 2f of a convex lens?
The image is real, inverted, and smaller.
What happens if an object is between f and 2f of a convex lens?
The image is real, inverted, and enlarged.
What happens if an object is at 2f of a convex lens?
The image is real, inverted, and the same size.
What happens if an object is closer than f in a convex lens?
A virtual, upright, and magnified image is formed
What type of image is formed by a concave lens?
Always virtual, diminished, and upright.
What is the principal axis?
The horizontal line passing through the center of the lens.
What does the power of a lens measure?
How strongly it refracts light.
Equation for power of a lens
P=1/f
What are the units of lens power?
Dioptres (D).
What type of lenses have positive power?
Convex lenses.
What type of lenses have negative power?
Concave lenses.
Why do short-sighted people need negative power lenses?
To spread out light rays and correct focus
Why do long-sighted people need positive power lenses?
To bring light rays to a focus.
How do multiple lenses combine their powers?
The total power is the sum of individual powers.
What is an example of lenses in combination?
A microscope.
What is the equation for total power of lenses in combination?
P(total)=P1+P2+P3+…
How do telescopes use multiple lenses?
To magnify distant objects
How does a zoom lens work?
By adjusting the distance between lens elements.
What happens if you combine a convex and concave lens?
Their powers partially cancel each other out.
What type of image does a convex lens usually form?
Real and inverted, unless the object is closer than the focal point, in which case it is virtual and upright.
What type of image does a concave lens always form?
Virtual, upright, and diminished.
How can you tell if an image is real or virtual using a ray diagram?
If rays actually meet, the image is real. If they only appear to meet when extended backward, the image is virtual.
Where are real images formed in a convex lens?
On the opposite side of the lens from the object.
What happens when an object is placed exactly at twice the focal length (2f) of a convex lens?
The image is real, inverted, and the same size as the object.
What is the lens equation?
1/f=1/u+1/v
Is focal length positive in convex lenses
Yes
Is focal length positive in concave lenses
No
What happens to the image distance v if the object distance u is decreased?
The image moves farther from the lens (for a convex lens).
What is the formula for magnification?
m=v/u
What does it mean if magnification m>1
The image is larger than the object.
What type of image has a negative magnification?
An inverted image.
What type of image has a positive magnification?
An upright image.
What does a magnification of 1 mean?
The image is the same size as the object.
What happens to magnification when an object is moved closer to a convex lens?
The magnification increases.
Why do microscopes have high magnification?
They use multiple lenses to enlarge tiny objects.
What is plane polarisation?
The restriction of wave vibrations to a single plane.
Which type of wave can be polarised?
Transverse waves.
Why can’t longitudinal waves be polarised?
Their vibrations are parallel to the wave direction.
What are common methods of polarisation? (2)
Polarising filters and reflection.
How does a polarising filter work?
It only allows light vibrating in one direction to pass through.
What happens when two polarising filters are at 90° to each other?
No light passes through.
What is interference?
The combination of two or more waves to form a new resultant wave.
What is superposition?
The principle that when two waves overlap, their displacements add together.
What are the two types of interference?
Constructive and destructive interference.
What happens in constructive interference?
The resultant wave has a larger amplitude than the individual waves.
What happens in destructive interference?
The resultant wave has a smaller amplitude than the individual waves.
What does it mean for waves to be coherent?
They have a constant phase difference and the same frequency.
Why is coherence important for interference patterns?
It ensures stable and consistent interference.
How can you tell if constructive or destructive interference is occurring?
If two waves meet at the same point (e.g., two crests), interference is constructive; otherwise, it’s destructive.
What does it mean for two points to be in phase?
They are at the same point in their wave cycle.
What is phase difference?
The angular difference between two wave cycles, measured in degrees or radians.
What is path difference?
The difference in the distance traveled by two waves to reach the same point.
How is path difference related to interference?
Constructive interference occurs when path difference is a whole number of wavelengths (nλ).
