Mod 4: Waves 2

Question 1

What are the properties of laser light

Answer 1

The light is coherent and monochromatic

Question 2

What is the definition of monochromatic?

Answer 2

There is only one wavelength present

Question 3

How can you demonstrate 2 source interference of EM radiation?

Answer 3

Point a laser source through a double slit. The slits will have to be around the same size wavelength that we waved and diffracted. The lights from the slits will then act like two coherent point sources.
You will then get a pattern of light and dark fringes on whether the interference is constructive or destructive. The destructive interference will have a path difference of half a wavelength, and it will be a dark fringe.
The lights fringe in the middle of the fringes will have a path difference of zero, and then the other light fringes will have a path difference of one wavelength.


Question 4

How do you find the wavelength from the two source interference for EM radiation experiment

Answer 4

Measure the French spacing, which is the distance from the centre of one of the minimum to the centre of the next minimum, or from one maximum to the centre of the other maximum to get an accurate value for the spacing measure across several fringes, and then divide the number by the number of fringe spacings between them

Question 5

Explain the young double split formula

Answer 5

Wavelength= ax/D
Where a= spacing between the slits
Where x= Fringe spacing
D= the distance from the slits to the Fringe spacing

Question 6

What is the difference between stationary and progressive waves?

Answer 6

Stationary waves do not transfer energy

Question 7

Define a stationary wave

Answer 7

A stationary wave is the superposition of two progressive waves, with the same wavelength, moving an opposite direction

Question 8

What is the equation for phase difference?

Answer 8

Length between 2 points in a wave/ wavelength X 360 or 2pi
X/l X 360

Question 9

When do you get stationary waves?

Answer 9

This happens due to the superposition of two progressive waves, which are the same wavelengths however, they are moving in the opposite direction. They have the same amplitude in the same frequency.

Question 10

What is the difference between an anti-node and a node?

Answer 10

An ant note is the point of the maximum altitude of a stationary wave, and the note is the point of zero, amplitude on a stationary wave

Question 11

What is the difference between stationary and progressive waves?

Answer 11

Progressive waves transfer energy, stationary waves don’t
Progressive waves have a constant amplitude across all points on the wave
However, in stationary waves, the amplitude varies as the nodes do not move at all so they have no amplitude

Question 12

What is the distance between two nodes or two anti- nodes in a stationary wave?

Answer 12

Half a wavelength

Question 13

What are harmonics?

Answer 13

How many are specific frequencies which create a stationary wave?

Question 14

Describe what is meant by the interference of waves

Answer 14

This is where two or more waves meet, and super pose, and the individual displacements on the waves combined to give a resultant displacement, which is equal to the vector sum of the individual displacement 

Question 15

How can we produce stationary waves

Answer 15

You can attach a vibration transducer at one end of a stretched string with the other end of the string fixed the signal generator will create a wave by vibrating the string
The progressive wave generated by the signal generator will reach the fixed end and reflect back onto it itself. These creates nodes and antinodes.
At the nodes the amplitude is zero, as the two waves are in Anti phase, therefore they have destructive interference
And at the antinodes the wave has maximum displacement as that is constructive interference and there is no phase difference, 

Question 16

Describe the characteristics of the first harmonic

Answer 16

The first harmonic will be vibrating at the lowest frequency compared to the other harmonics. It has two nodes add one antinodes
It is the length of half wavelength as the distance between two nodes is half a wavelength

Question 17

Describe the characteristics of the second harmonic

Answer 17

It has three nodes and, two antinodes
It is the length of one whole wave
and the frequency is double the fundamental frequency

Question 18

Describe the characteristics of the third harmonic

Answer 18

There are four nodes
And three antinodes
It has a length of one and a half waves
And the frequency is three times the fundamental frequency

Question 19

What would the fourth harmonic look like and what would we have to do to create it?

Answer 19

We would have to multiply the fundamental frequency by four
There would be four antinodes
And 5 nodes
And the string will have the length of two whole waves

Question 20

 when 2 sign waves of slightly different frequencies, superpose they will alternate between interfering, constructively and destructively. This is called a beat pattern .
suggest how the phenomenon of beat patterns can be used by a piano, tuna to tune a piano string

Answer 20

The piano tuna should strike the piano string, and the tuning fork at the same time. They should then adjust the pitch of the piano string until the sound can no longer be heard. This means both of the waves are coherent

Question 21

Define coherent

Answer 21

Two sources are coherent if they have the same wavelength and frequency and a fixed phase difference between them

Question 22

Unlike progressive waves, stationary waves do not transmit energy with reference to how stationary waves are formed. Suggest why stationary waves do not transmit energy.

Answer 22

The progressive waves that form the stationary waves travel, and transfer energy in opposite directions. Therefore, the energy cancelled out, so there is no energy transfer.

Question 23

What is the conditions for constructive interference?

Answer 23

There must be a phase difference of 0°, or any multiple of 360°

Question 24

What is the equation for the path difference of constructive interference?

Answer 24

N X wavelength
Where the N is an integer, which is the distance between two points on a wave

Question 25

What is the equation for destructive interference for path difference?

Answer 25

(N + 1/2) X wavelength

Question 26

Describe what the first harmonic would look in an air column

Answer 26

The length would equal a quarter of the wavelength this is because the length would be half of the length of the first harmonic as in air columns. There is one open end and one closed end at the closed end. There will be node and at the end there will be antinodes Therefore, to find the wavelength of the wave, we must multiply the length by four

Question 27

Why does a node form at the closed end of an air column?

Answer 27

Because the air molecules cannot oscillate when they are faced with a solid boundary therefore they will have no displacement

Question 28

Describe an experiment to find the speed of sound

Answer 28

Place a cylinder in a tub of water. The amount of water in the cylinder will vary the length of the air column. Then bang a tuning fork on a surface and hold it above the air column. When you can hear the sound, measure the length of the tube, without water, then multiply the length by 4 to get the wavelength of the wave. You can then plot a graph of length against the time period which is one divided by the frequency This will give you the gradient which wall equal wave speed divided by four, therefore, to find the speed of sound you multiply the gradient by four

Question 29

Describe an experiment in order to find the refractive index of a block when you have the materials if the block Reebok and a piece of paper

Answer 29

Place a Roblox on top of a piece of paper and very the angle of incident using the box using a pencil draw the path of the incident and the angle of refraction created and use a protractor to find the angle of incident and the angle of refraction, then plot graph of angle of incident against angle of refraction so that the gradient of the graph is the refractive index of the block as the refractive index of air is one so sign theta equals refractive index times sign the two

Question 30

In the double split experiment using speakers maximum and minimise are produced. What would happen if you swapped the speakers around

Answer 30

The minimum would become maxima and the maximum would become minimum

Question 31

Define phase difference

Answer 31

How far out of sync the oscillations are at 2 points on the wave

Question 32

Give 1 similar and 1 different of points on the same wave

Answer 32

Similar - same frequency Diff- diff phase difference

Question 33

The frequency of a stationary wave is 30Hz explain the lowest possible frequency of oscillation when all the points can be in phase on the string. The string at 30Hz has a length= wavelength

Answer 33

The 1st harmonic is the lowest possible frequency as the L= wavelengths so this is the 2nd harmonics at 30 hz, therfore lowest frequabcy is 15Hz

Question 34

2 speakers are attached to an oscillator and are at a distance of D away from a detector, as this detector is moved perpendicularly to the floor explain why the amplitude of the detected signal changes

Answer 34

The path difference between the signals and the detector changes., therefore the detected signal varies between max and min due to constructive or destructive interference

Question 35

2 speakers are at a distance D from a detector, the distance D increases explain why the amplitude of the detected signal changes

Answer 35

As D increases I decrease I is proportional to A squared therfore a also decreases this is due to the energy emitted by the transmitters spread out therfore less is collected by the detector the further away it is

Question 36

2 speakers are at a distance of D from a detector, one of the speakers is moved further back , a minimum is detected at the detector explain why and what is the equation to find this distance the speaker has moved for this min signal

Answer 36

Waves are in antiphase therfore no signal detected , antiphase detected from both leakers D= avelength/2 , as path diff= (n+1/2) x lambda , we are not given n

Question 37

2 microwave transmitters are at a distance D from a detector , the detector is rotated to about 90 degrees explain what will happen happen to the signal detected

Answer 37

At 90 degrees recover ill only receive horizontally polarised waves The me are vertically polarised therfore the receiver is perpendicular to the plan polarisation of the me so no signal wil be detected

Question 38

Two speakers are at a distance d from a detector, a minimum spot is created, explain why this spot will be a spot of minimum intensity but not 0 intensity

Answer 38

The waves are in antiphase therfore destrctive interference However there will be a resultant amplitude therfore there is still intensity and sound will still be heard

Question 39

A double split experiment is performed using a light with wavelength lambda the centre of the observed pattern is a bright fringe. What is the path difference between two waves which interfere to give the third dark fringe from the centre?

Answer 39

For a dark fringe, the path difference must be an odd multiple of the half wavelength Therefore, the first dark fringe will be lamb over two The second dark fringe would be lambda over two as it must be odd So the third dark fringe would be lambda over two which is 2.5 lambda