P5 - Waves and Particle Nature of Light

What do waves transfer

Energy but not matter

Water waves caused by

Vibrations or oscillations

What is a phase

Position of a certain point on a wave cycle - degrees radians or fractions of a wave

What is a path difference

The distance between two points of a wave

Whenis a standing wave formed

Formed when two progressive waves travel in opposite directions at the same place with the same frequency wavelength and amplitude

what are resonant frequencies

The exact number of waves created in the time it takes for a wave to reach the end and back The original waves reinforce each other

At resonant frequencies and exact number of half wavelengths are produced

At what type of frequencies do standing waves occur

In resonant frequencies

What are nodes

Points on a wave where there is no vibrations - 0 development

What are antinodes

Points on a wave where there is a maximum displacement

How is a standing node formed

A wave traveling down the string is reflected from the other end

The waves superpose in opposite directions

This causes is constructive interference at the antinodes

This causes destructive interference at the nodes

The water conditions for a standing wave

The same wavelength

The same frequency

The same amplitude

If the length of the string is what is the wavelength of a wave in the first harmonic

2L

If the length of a string is L what is the length of the wave for the second harmonic

L

Where are nodes found in microwaves reflected off a metal plate

Notes can be found by moving the probe between the transmitter and reflecting plate

What happens to powder when a loudspeaker is placed and sound is played through a glass tube

The powder gets pushed away from the anti nodes and onto the nodes

Stationary waves are created in the tube

What are factors that affect the resonant frequencies of a string

The longer the string the lower the resonant frequencies Half wavelengths lower at resonant frequencies

The heavier the string the lower the resonant frequencies as the wave travels more slowly down the string

The looser the string the lower the resonant frequency as waves travel more slowly down the loose string

What does intensity mean

The rate of flow of energy per unit area at right angles to the direction of energy transfer

What is the formula of intensity with power and area

Intensity = power/area

What is Intensity proportional to

intensity = Amplitude²

When does superposition happen

When two or more waves pass through each other

What happens to the displacement when superposition happens

The resulting displacement equals the vector sum of the individual displacements

what can complex waves be separated as

Separated out mathematically into several simple waves of various sizes

What is interference

When two or more waves superpose with each other

What is constructive interference

trough plus trough gives a bigger trough and Crest and Crest gives bigger Crest

What is destructive interference

trough plus Crest cancel each other out

How is interference made noticeable

By having two amplitudes be equal to each other

How are two points in phase

If they are both at the same point in the wave cycle

What happens to the displacement and velocity when two points are in phase

They have the same displacement and velocity

How do you know if two points are in phase

If the phase difference is zero or multiple of 360

How do you know if two points are out of phase

If the phase difference is odd number multiples of 180 like 1pi, 3pi and 5pi

What does coherent mean

They have the same wavelength and frequency and fixed phase difference between them

What are Wave fronts?

Imaginary planes that cut across all waves join points that are in phase

What is the distance between each wavefront

One wavelength

How to get clear interference patterns

Two or more sources should be coherent

What should be the distance between points for constructive interference in terms of wavelength

nλ

What should be the distance between two points for destructive interference

When there is an odd number of half wavelengths

(2n+1)λ /2

What type of interference occurs when points are in phase

Constructive interference

What type of interference occurs when points are out of phase

Destructive interference

What is diffraction

Waves are spread out as they come through a narrow gap or go around obstacles

What are Ripple Tanks

Shallow tanks of water you can generate a wave in

How do ripple Tanks work

They use an oscillating paddle to create regular waves with parallel wave fronts

What happens to sound and light near a doorway

When sound passes through a doorway the size of the gap doorway is roughly equal so a lot of diffraction occurs

You cannot see well because light has such a much smaller wavelength so diffraction is very small

What is Huygen’s construction

Every point on a wavefront may be considered to be a point source of secondary wavelets that spread out in the forward direction at the speed of the wave the new wavefront is the surface that is tangential to all these secondary wavelets

How can Huygen’s construction be used to explain the shape of the wavefront as light travels through the slit

The secondary wave front that passes through the slick produces the curve of the new wavefront emerging from the slit

What happens when waves meet an obstacle

There is diffraction around the edges behind the obstacles there are shadows where wave is blocked

What happens to diffraction with a wider object

The more the diffraction and the longer the shadow

What forms when wavelength is as big as the gap

You get a light and dark diffraction pattern

What happens to the diffraction pattern when wavelength compared to the width is longer

The diffraction pattern is wider

What happens when you pass one wavelength beam of light into 2 slits?

The slits cut the light and diffract them to produce two coherent sources of light, and produce alternating bands of light

What happens when you pass one wavelength beam of light into multiple slits?

With more number of equally spaced slits, you get the same shape but with brighter bands and more narrow, while dark areas are more darker

Why do sharper fringes make more precise measurements

It is easier to tell apart so i is easier to measure

How do the maximas appear for monochromatic light?

Maximas are sharp light

Where is the line of maximum brightness in a diffraction grating?

0 order line

What is the formula for slit spacing?

d = 1/N, where N is slits per metre

What is the formula for the first order fringe with 0 order line, with firnge width and distance between grating and wall?

θ = x/D

What happens to the pattern of the diffraction grating when wavelength increases?

The pattern spreads out more

What happens to the pattern when spacing of the slits increases?

Pattern spreads out less

How do you know if an order does not exist?

If sinθ > 1

What happens when white light diffracts through a grating?

Pattern is spread out by different amounts. Each order becomes a spectrum with red on the outside and purple on the inside. White 0 order has white as all wavelengths pass through

Why do astronomers and chemists study spectra

To identify elements, diffraction gratings used as they are more accurate than prisms

How do CDs and DVDs make use of diffraction?

CDs and DVDs have grooves on reflective surfaces which cause light to diffract.

Constructive interreference occurs at different points with different wavelengths, so there is a rainbow pattern