# Physics - Recall for Chapter 12: Waves II

> Source: https://ollybritton.com/notes/a-level/physics/recall-questions/chapter-12-waves-ii/ · Updated: 2021-08-03 · Tags: physics, school, waves, waves-ii, recall-questions

## Recall Questions
##### State what is meant by the superposition principle??
When two or more waves meet at a point, the resultant displacement is the vector sum of the displacements of the individual waves.

##### State what is meant by coherent waves??
Waves that have a constant phase difference.

##### State the conditions for two waves to be coherent??
The waves must be of the same type and have the same frequency.

##### State what is meant by interference??
The superposition of waves from coherent sources.

##### State the conditions needed to observe constructive interference??
Waves must be in-phase, meaning a phase difference of $0$ or an even number of $\pi$ and a path difference of an integer number of wavelengths $(n\theta)$.

##### State the conditions needed to observe destructive interference??
Waves must be in anti-phase, meaning a phase difference of an odd number of $\pi$ and a path difference of $n + \frac{\lambda}{2}$.

##### Define the terms in the equation for $$\lambda = \frac{ax}{D}$$ and the assumption you make in deriving it??
* $\lambda$ is wavelength,
* $a$ is the slit separation,
* $x$ is the separation between adjacent fringes, and
* $D$ is the slit-screen distance.

Assumption is that $a >> D$.

##### Why did Young setup a single slit before the double slit in his original experiment??
To ensure the waves from each of the double slits was coherent so that a stable interference pattern could be observed.

##### How else can inteference effects be observed, apart from using visible light??
By using a pair of speakers connected to the same power supply, or a signle microwave emitter directed at two slits in a metal plate.

##### Describe how a stationary wave can be formed??
The superposition of two progressive waves with the same frequency and similar amplitudes travelling in opposite directions.

##### State what is meant by a node on a stationary wave??
A point of zero amplitude.

##### State what is meant by an antinode on a stationary wave??
A point of maximum amplitude.

##### State the separation of adjacent nodes on a stationary wave??
$\frac{\lambda}{2}$

##### State the phase difference between points between adjacent nodes on a stationary wave??
$0$ radians.

##### State the phase difference between points on either side of a node on a stationary wave??
$180^{\circ}$ or $\pi$ radians.

##### State three differences between progressive waves and stationary waves (long)??
1. Progressive waves transfer energy, stationary wave do not.
2. The amplitude of all points on a progressive wave are the same, the amplitude of points on a stationary waves varies between $0$ and $1$.
3. The phase difference between points on a progressive wave vary from $0^\circ$ to $360^\circ$, the phase difference for points in a stationary wave vary from $0^\circ$ to $180^\circ$.

##### State what is meant by the fundamental frequency of a stationary wave??
The lowest frequency of vibration for a given arrangement.

##### State what is meant by the first harmonic (fundamental mode)??
A stationary wave that has a frequency equal to the fundamental frequency. All other harmonics have a frequency that is a multiple of the fundamental frequency.

##### What will always be found at the ends of a stationary wave pattern produced on a vibrating string fixed at each end??
Nodes.

##### State how a stationary wave can be produced using sound waves (long)??
Holding a vibrating tuning fork above a pipe/tuve open at one or both ends. An increase in loudness of the sound will be heard when a stationary wave pattern is produced.

##### What will always be found at the ends of a stationary wave pattern formed by a column of air vibrating in a pipe/tuve closed at one end??
Node at the closed end and an antinode at the open end.

##### What will always be found at the ends of a stationary wave pattern formed by a column of air vibrating in an open tube/pipe?
Antinodes at both ends.

##### Describe how a stationary wave can be produced using microwaves (long)??
Reflect microwaves from a microwave emitter using a metal plate. The incident and reflected waves will superpose to produce a standing wave. Move a microwave detector between the emitter and metal plate to detect the presence of nodes and antinodes.

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