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Physics > Waves > Flashcards

Waves Flashcards

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1
Q

What direction do waves transfer energy?

A

They transfer in the direction they are travelling

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2
Q

What are Transverse waves?

A

The oscillations of the waves are perpendicular to the direction of travel

  • All electromagnetic waves (light)
  • Ripples and waves in water
  • a wave on a string
  • S waves
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3
Q

What are Longitudinal waves?

A

The oscillations of the wave are parallel to the wave of travel

  • Sound waves in air (ultrasound)
  • Shock waves (some seismic waves)
  • P waves
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4
Q

What is frequency?

A

the number of complete waves passing a certain point per second
- Hertz (Hz)

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5
Q

What is Wave speed?

A

the speed at which energy is being transferred
OR
the speed the wave is moving at

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6
Q

What is an oscilloscope?

A

A device for viewing oscillations on a screen

  • measure the speed of sound
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7
Q

How do you use an oscilloscope to measure the speed of sound?

A
  • Set up an oscilloscope connected to 2 microphones near a speaker. So detected waves at each microphone are shown as seperate waves
  • Start with both mics next to the speaker, then move one away slowly until the 2 waves are aligned on display, but moves 1 wavelength apart
  • Measure the distance between the mics to find the wavelength
  • Use wave speed equation to find wave speed (should be around 330 m/s)
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8
Q

What can happen to a wave when it arrives at a boundary between 2 different materials?

A
  • Can be Absorbed
  • Can be Transmitted
  • Can be Reflected
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9
Q

What happens if a wave is absorbed by the material it’s crossing into?

A

It transfers energy to the material’s energy stored

  • microwave
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10
Q

What happens if a wave is transmitted through the material it’s crossing into?

A

The waves carry on travelling through the new material, often leading to refraction

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11
Q

What happens if a wave is reflected on the material it’s trying to cross into?

A
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12
Q

What does a wave being absorbed, transmitted and reflected depend on?

A
  • wavelength
  • properties of the materials involved
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13
Q

What is the rule applies to all reflected waves?

A

Angle of Incidence= Angle of Reflection

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14
Q

What is the angle of incidence?

A

the angle between the normal and the incoming ray

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15
Q

What is the angle of reflection?

A

the angle between the normal and the reflected ray

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16
Q

What is the normal

A

a line that is perpendicular (at right angles) to the surface at the point of incidence

  • usually shown as a dotted line
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17
Q

What is the point of incidence?

A

the point where the wave hits the boundary

18
Q

What is Specular reflection?

A

a wave is reflected in a single direction by a smooth surface

  • mirror
19
Q

What is Diffuse reflection?

A

a wave is reflected by a rough surface, reflected rays are scattered in lots of different directions

  • piece of paper
20
Q

Why does Diffuse reflection occur?

A
  • normal is different for each incoming ray, angle of incidence differs
  • surface appears matte, no clear reflection on the surface
21
Q

Are EM waves transverse or longitudinal waves?

A

Transverse waves

22
Q

What are Electromagnetic waves?

A

Transverse waves that transfer energy from a source to an absorber

  • travel at the same speed through air or a vacuum
  • grouped into 7 basic types based on wavelength + frequency
23
Q

What is a vacuum?

A

an area with no matter/particles

24
Q

What is the Electromagnetic spectrum order?

A

Radiowaves
Microwaves
Infrared radiation
Visible light
Ultraviolet
X-rays
Gamma rays

25
Q

As the EM spectrum goes down does it increase or decrease in frequency and wavelength?

A

It has an increasing frequency and a decreasing wavelength

Radiowaves- low frequency, long wavelength

Gamma rays- high frequency, short wavelength

26
Q

What is refraction?

A

When a wave crosses a boundary between materials at an angle, and changes direction

27
Q

What does the amount a wave is refracted by depend on?

A
  • ## How much the wave speeds up or slows down (depends on density of the 2 materials, higher density= slower the wave travels through)
28
Q

What is FAST

A

F- fast
A- away
S- slow
T- towards

If a wave crosses a boundary and slows down, it will move towards the normal

If a wave crosses a boundary and speeds up, it will move away from the normal

29
Q

What changes when a wave is refracted?

A

The Wavelength of a wave CHANGES but Frequency STAYS THE SAME

30
Q

What happens to a wave if it is travelling along the normal?

A
  • Changes speed
  • NOT refracted
31
Q

What is Optical density of a material?

A

A measure of how quickly light can travel through said material

the higher Od, the slower light waves travel through

32
Q

What are EM waves made up of?

A

Oscillating electric and magnetic fields

33
Q

How are Radiowaves produced?

A
  • Use an alternating current in an electrical circuit
  • Transmitter- charges electrons to oscillate to create radiowaves
  • transmitted radiowaves are recieved by the Receiver
  • energy carried by wave is transferred to receiver electrons
  • causes electrons to oscillate and if its a complete circuit, creates AC current
  • This current has the same frequency as the radio wave that generated it
34
Q

What are uses of Radiowaves?

A

Wavelength= longer than 10cm
- Long-wave radio-> 1-10km wavelength, bend/diffract around curved surface of earth, hills, tunnels etc, Can be recieved even if receiver isn’t in line of sight

  • Short-wave radio-> 10-100m wavelength, long distances, reflected from ionosphere (electrically charged layer of earth’s upper atmosphere)
  • Bluetooth-> sw radio waves, sends data over short distance without wires
  • Medium-wave signals-> can sometimes reflect from ionosphere (if they are short), depends on atmospheric condition + time of day
  • TV and FM radio transmission (sw radio waves), direct signal of transmitter (no bending or long distance travel)
  • communication
35
Q

What are uses for Microwaves?

A
  • Communication between satellites (tv signal, satellite phones): Passes easily through earth’s atmosphere
  • Microwave ovens: microwaves absorbed by food molecules, penetrate a few cm before being absorbed, transfers energy, heating water thus heating food
36
Q

How does satellite TV work?

A
  • Signal from transmitter is transmitted into space
  • picked up by satellite dish (receiver), transmits signal back down to earth
  • received by satellite dish on the ground (slight time delay due to long distance of travel)
37
Q

What are uses for Infrared radiation?

A
  • Infrared camera: detect IR radiation and monitor temperature, turns temp into electrical signal, displayed on the screen as a picture. Hotter= brighter
  • Cooking food: causes objects to get hotter, ie toast from toaster
  • Electrical heaters heating a room: long piece of wire that heats + glows with a flowing current, emits high IR radiation, absorbed by objects and the surroundings and air. Energy transfers to their thermal energy stores, causing their temp to increase
38
Q

What objects is Infrared radiation emitted by?

A

All objects

  • the hotter the object, the more radiation given out
39
Q

What are fibre optic cables?

A

Thin glass or plastic fibred that carry data (from telephones, computers etc) over long distances as pulses of visible light
- reflection, bounce back and forth until end of fibre
-visible light
- not easily absorbed or scattered

40
Q

What are uses for UV radiation?

A

Fluorescence-> UV is absorbed, visible light is emitted, looks bright

Energy efficient lights, used for long periods (classrooms)

Security pens (ink only glows under UV light)

UV radiation from Sun-> gives tan

Tanning salons-> UV lamps, artificial suntan. Overexposure=dangerous

41
Q

What are uses of X-rays and Gamma rays in medicine?

A

X-ray photos-> broken bones
Easily pass trhough flesh, not dense material like bones/metal

Treat cancer (radiotherapy), high doses kill all living cells, carefully directed, avoid killing too many healthy cells

Gamma-> medical tracer, pass trhough the body undetected

can be harmful- wear lead aprons, lead screen, stand outside room to keep exposure to minimum

42
Q

How can EM radiation be harmful?

A

Physics (18 decks)

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