Waves

Question 0

Wavelength

Answer 0

The distance between corresponding points in the wave (one crest to the next cress in a transverse wave)

OR

The distance between two adjacent points of similar displacement

Question 1

Amplitude

Answer 1

The maximum displacement of a part of the medium from its rest position

Question 2

Period of a wave

Answer 2

The time for one complete cycle of the waveform

Question 3

Difference between longitudinal and transverse waves?

Answer 3

Transverse - the vibrations are perpendicular to the direction of energy transferred (light, EM spectrum waves) - shown by slinky up and down/ripples on water

Longitudinal - the vibrations are parallel to the direction of energy transferred (sound, ultrasound) - shown by pushing a slinky in front

Question 4

Waves transfer energy or matter?

Answer 4

Waves transfer energy and information without transferring matter!

Question 5

What can happen to all waves?

Answer 5

All waves can be reflected, refracted, diffracted (when they pass an edge)

Question 6

What’s diffraction?

Answer 6

the spreading out of wave. they bend around edges and through gaps, causing the waves to spread out. (this allows waves to travel around corners)

Question 7

What affects the extent of diffraction?

Answer 7

The amount of diffraction depends on the size of the gap relative to the wavelength of the wave.

When gap is same length as wavelength - MAXIMUM diffraction
When gap much bigger than wavelength - little diffraction

(Longer the wavelength, more they diffract)

Question 8

All waves in the (continuous) electromagnetic spectrum…

Answer 8

All transverse waves
All travel at the same speed in free space/ a vacuum
(3 x 10^8 m/s)

Question 9

What’s the law of reflection?

Answer 9

angle of incidence = angle of reflection

Question 10

Describe experiments to investigate the refraction of light, using rectangular blocks, semicircular blocks and triangular prisms

Answer 10

Place a block of glass on a piece of paper, draw an outline.

At one point, draw the normal line. Trace the incident Ray and emergent Ray (that comes out the other side of block.) remove block and draw in refracted Ray inside block.

(As light passes from air into block (denser medium), it bends towards the normal because it slows down. Some light is reflected at boundary. It then speeds up again and bends away from normal.

Measure the angle of the emergent ray.

Repeat for different shaped glass.

Question 11

What’s the relationship between refractive index, angle of incidence, and angle of refraction? (The law of refraction/ SNELL’S law)

Answer 11

n = sin i
      -----
      sin r (angle of refraction)

Question 12

Describe an experiment to determine the refractive index of glass, using a glass block:

Answer 12

Shine a ray of light through a glass block, measure the angle of incidence and the angle of refraction. (Protractor)
Do sin(i) divided by sin(r) and you will have the refractive index of glass.

Question 13

Use semicircular blocks to show total internal reflection:

Answer 13

Semi circular blocks - high to low refractive index, speeds up.

Increasing the angle of incidence, the angle of refraction gets closer to 90 degrees. Eventually it equals critical angle C for which r = 90 degrees, the light is refracted along the boundary.

Incident Ray aimed at curved edge so that it always enters at right angles to the edge. (Doesn’t bend as it enters the block, only when it leaves from straight edge)

Mark positions of rays and block on paper and measure angles w protractor.

Question 14

Relationship between critical angle and refractive index.

Answer 14

sin C = 1
—
n

Question 15

Optical fibres with total internal reflection

Answer 15

Optical fibres made of glass or plastic have a central core surrounded by cladding w a lower refractive index.

The core is so narrow that light signals passing through always hit the core-classing boundary at angles higher than C - light is always totally internally reflected.

Stops working if fibre bent too sharply

Question 16

What’s refractive index?

Answer 16

Refractive index of a material is a measure of the change in speed of light as it passes from a vacuum (or air as an approximation) into the material.

High refractive index (glass) - light slows down a lot in glass

Low refractive index (water) - light doesn’t slow down so much in water

Question 17

Explain critical angle c?

Answer 17

The angle at which the angle of incidence must reach for angle of refraction to reach 90 degrees and for total internal reflection to take place.

Question 18

What’s total internal reflection?

Answer 18

Where no light leaves the medium and all is reflected internally. Where angle of incidence is greater than the critical angle (C) so that the angle of refraction is greater than 90 degrees.

i less than critical angle - most of light passes out, little bit internally reflected

i equal to critical angle - emerging Ray comes out along surface. lot of internal reflection

i greater than critical angle - total internal reflection. no light comes out.

Question 19

What’s the frequency range for human hearing?

Answer 19

20 Hz - 20,000 Hz

Question 20

What are sound waves caused by?

Answer 20

Longitudinal waves caused by vibrating objects blue vibrations are passed through the surrounding medium as a series of compressions and then may reach someone’s eardrum.

The denser the medium, the faster the sound travels. (More vibrating particles) cannot travel in a vacuum.

Question 21

Explain sound waves being reflected, refracted, diffracted:

Answer 21

Reflected by hard flat surfaces. Carpets and curtains act as absorbing surfaces - absorb sounds.

Sound waves refract, change shape in different media but since they spearhead up so much, hard to spot their change in direction

Diffracted through gaps, obstacles. Hear someone talking from around a corner or outside a room (waves bend and spread out)

Question 22

Describe an experiment to measure the speed of sound in air:

Answer 22

By attaching a signal generator to a speaker, you can generate sounds with a specific frequency.

Attach two microphones and an OSCILLOSCOPE to find the wavelength of the sound waves generated. Detected waves at each microphone can be seen as a separate wave on the oscilloscope.

Start with both mics next to speaker and slowly move one away until the two waves are aligned on the display, exactly one wavelength apart. (Measure distance between mics = lambda; wavelength)

v = f x wavelength

f = what you sent the signal generator to in the first place (around 1 kHz)

Check that 340m/s

Question 23

How can an oscilloscope display sound waves?

Answer 23

A sound microphone (a sound wave receiver) picks up sound waves travelling through air and to display them and measure their properties, plug the mic into an oscilloscope.

Mic converts sound waves to electrical signals. Oscilloscope displays microphone signal as a trace on a screen.

The appearance of the wave on the screen tells you whether it’s loud/quiet, high-/low-pitched.

Question 24

What’s the relation between pitch and sound, loudness and amplitude?

Answer 24

The greater the amplitude of wave/vibration, the more energy it carries and therefore the louder it is. ➡️ Louder sounds-trace w a larger amplitude on an oscilloscope

Higher the frequency, higher the pitch

Question 25

Describe an experiment to determine frequency of a sound wave with a oscilloscope

Answer 25

Horizontal axis on the display = TIME
time between each division on scale can be adjusted to get a clear, readable trace.

Adjust time division setting until display shows at least 1 complete cycle.

Read off the period (time taken for one complete cycle). Where 1 cycle takes x amounts of divisions, where each division is y. Multiply x by y = s

Frequency = 1/ time period

(s = time period)