Topic 5 - Waves and the Particle Nature of Light Flashcards
What is a wave’s amplitude?
The amplitude of a wave is its maximum displacement from its equilibrium position
The magnitude of the maximum displacement reached by an oscillation in the wave
What is a wave’s frequency?
The frequency of a wave is the number of complete waves that pass a point per second
What is meant by the period of a wave?
The period of a wave is the length of time taken for one complete wave to pass a given point
The time taken for one complete oscillation at one point on the wave
How are frequency and period linked?
Frequency = 1/period
They are reciprocals of each other
What is wavelength?
The distance between the same point on two adjacent waves (peak-to-peak or trough-to-trough)
State the equation used to calculate a wave’s speed.
v = f λ
Speed = frequency x wavelength
Describe a longitudinal wave.
Particle oscillations are parallel to the direction of the wave’s motion / movement of the wave energy
Consists of rarefactions (low pressure regions), and compressions (high pressure regions)
Describe a transverse wave.
Particle oscillations are perpendicular to the direction of the wave’s motion / movement of the wave energy
Consists of peaks (maximum positive displacement), and troughs (maximum negative displacement)
What is a progressive wave?
A progressive wave is one that transfers energy from one point to another without any transfer of matter
Transferring energy via oscillations
What is a standing wave?
A wave that stores energy rather than transferring it from one place to another
Consists of oscillations in a fixed space, with regions of significant oscillation and regions with zero oscillation, which remain in the same locations at all times
What is path difference a measure of?
Path difference is a measure of how far ahead one wave is compared to another
The difference in distance that two waves must travel from their sources to a given point
What is a wave’s phase?
A wave’s phase at a given point is a measure of how far through its cycle the wave is. It is usually measured in radians, where a complete cycle is 2π
What is the phase difference between two waves at a given point?
The phase difference is the difference between the phases of the two waves - in other words, it is a measure of the difference between how far each wave is through its cycle
What happens when two waves meet?
The two waves will interfere with each other
What happens when two waves meet in phase?
They will interfere and undergo constructive interference
What happens when two waves meet in anti-phase?
They will interfere and undergo destructive interference
How is a standing wave formed on a string?
- a wave reflects from a closed end meaning two identical waves are travelling in opposite directions down the same string
- at points where the waves meet in phase, constructive interference occurs and an anti-node is formed
- at points where the waves meet in anti-phase, destructive interference occurs and a node is formed
What is a node?
A node is a point of minimum displacement - there is no movement from the equilibrium position
Nodes are regions on a stationary wave where the amplitude of oscillation is zero
What is an antinode?
An antinode is a point of maximum displacement
Antinodes are regions on a stationary wave where the amplitude of oscillation is at its maximum
What two factors does the speed of a transverse wave on a string depend on?
(Give the equation)
- tension
- mass per unit length of the string
v = √(T/μ)
State the equation used to calculate intensity.
I = P/A
I - intensity
P - power
A - area
What is the refractive index of a material through which light travels a speed of ‘v’?
n = c/v
Where c is the speed of light in a vacuum
State the equation linking the refractive indexes and angles at an interface between two mediums.
n1sinθ1 = n2sinθ2
What is the critical angle?
The angle of incidence for which the angle of refraction is 90° and all the light passes along the boundary between the mediums. Beyond this angle all light will be reflected
The critical angle is the largest angle of incidence that a ray in a more optically dense medium can have and still emerge into less dense medium. Beyond this angle, the ray will be totally internally reflected
State the equation used to calculate a critical angle.
sinC = 1/n
What is total internal reflection?
Total internal reflection is where all the light is reflected back at the boundary between two mediums. It occurs when light is incident at an angle greater than the critical angle.
Total internal reflection requires two conditions to be met:
- the ray is attempting to emerge from the more dense medium
- the angle between the ray and the normal to the interface is greater than the critical angle
What is the focal point of a converging lens?
The single point where the parallel rays of light entering the lens converge (intersect on the opposite side of the lens)
Rays of light from a distant object will arrive at the lens parallel to each other. A converging lens will bring these rays together at a point (focal point)
What is the focal point of a diverging lens?
Parallel light rays diverge and can be traced backwards until they intersect at a point (focal point).
Rays of light from a distant object will arrive at the lens parallel to each other. A diverging lens will spread these rays apart so they will not meet at a point.
What is the focal length of a lens?
The distance between the centre of the lens and the focal point
What is the equation used to calculate the power of a lens?
Power = 1/focal length
How do you calculate the total power of a combination of thin lens?
P = p1 + p2 + p3 + …
What is a real image?
A real image is one that can be projected onto a screen and is always inverted. Real images are the consequence of light meeting at a focal point.
A real image:
- can be projected onto a screen
- is always on the other side of the lens from the real object
What is a virtual image?
Virtual images are the consequence of rays of light appearing to meet at a point. They cannot be projected onto a screen.
A virtual image:
- cannot be projected onto a screen
- is on the same side of the lens as the real object
State the equation used to calculate the magnification of an image.
Magnification = (image height) / (object height)
M = I/A
What is plane polarisation?
Plane polarisation is when the oscillations of a wave are restricted to a single plane.
Polarisation refers to the orientation of the plane of oscillation of a transverse wave. If the wave is (plane) polarised, all its oscillations occur in one singular plane
