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Physics > Waves 1 > Flashcards

Waves 1 Flashcards

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1
Q

What is a progressive wave?

A

A progressive wave is an oscillation that travels through matter.

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2
Q

Explain why sound is a progressive wave.

A

Because vibrations travel towards your ears, but the air particles do not.

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3
Q

What is a transverse wave?

A

In a transverse wave the oscillation or vibrations are perpindicular to the direction of energy transfer.

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4
Q

Give an example of transverse wave.

A

Waves on the surface of water.
Any electromagnetic wave i.e: Radio waves, microwaves, etc.
Waves on stretched strings.

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5
Q

What is a longitudinal wave?

A

In a longitudal waves the oscillations are parallel to the direction of energy transferred.

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6
Q

Give an example of longitudinal wave.

A

Sound waves or waves produced from Earthquakes.

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7
Q

What is compression?

A

The decrease in length of an object when a compressive force is exerted on it.

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8
Q

What is rarefaction?

A

The change in direction of a wave as it changes speed when it passes from one medium to another.

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9
Q

Define the time period of an oscillation

A

The time take for one oscillation or the time taken for a wave to move one whole wave length past a given point.

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10
Q

Define the frequency of an oscillation.

A

The number of wavelengths passing a given point per unit time. The number of oscillation completed per unit time.

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11
Q

What is a wave profile?

A

A graph showing the displacement of th eparticles in the wave against the distance a long the wave is sometimes called a wave profile.

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12
Q

What is phase difference?

A
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13
Q

What are the units of phase-difference?

A

Degrees or radians.

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14
Q

What does it mean if to particles are in phase?

A

When particles are in phase, they are oscillating perfectly in step with each other (Both reaching their max positive displacement at the same time).

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15
Q

What does it mean if particles are in antiphase?

A

When particles are in antiphase, they are oscillating completely out of step with each other (One reaches the maximum positive displacement at the same time as the other reaches its maximum negative displacement). They have a phase difference of 180 degrees or Pi radians.

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16
Q

What piece of scientific equipment can be used to determine the frequency of a wave?

A

An oscilloscope can be used to determine the frequency of a wave.

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17
Q

What is a reflection of a wave?

A

Reflection occurs when a wave changes direction at a boundary between two different media, remaining in the original medium.

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18
Q

State the law of reflection.

A

The law of reflection applies whenever waves are reflected. It states that the angle of incidence is equal to the angle of reflection.

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19
Q

When a wave if reflected, do the wavelenght or frequency change?

A

When a wave is reflected, its wavelength and frequency does not change.

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20
Q

What is refraction?

A

Refraction occurs when a wave changes direction as it changes speed when it passes through on medium to another.

21
Q

Describe what happens if a wave slows down upon entering a difference medium.

A

If a wave slows down it will refract towards the normal.

22
Q

Do sound waves speed up or slow down when entering a denser medium.

A

Sound waves normally speed up when entering denser medium.

23
Q

Do light waves speed up or slow down when entering a denser medium.

A

Electromagnetic waves such as light normally slow down.

24
Q

What happens to water waves when they enter shallower water?

A

When a water wave enters shallower water, it slows down and the wavelength gets shorter.

25
Q

What is diffraction?

A

Diffraction is a property to unique waves. When a wave passes through a gap or travels around an obstacle, they spread out.

26
Q

Do the speedd, frequency and wave-length of the wave change when diffracted?

A

The speed, wavelenght and frequency of a wave do not change when diffraction occurs.

27
Q

Under what conditions are diffraction effects most signficant.

A

Diffractions are most effective when the size of the gap or obstacle.

28
Q

Explain why a smaller gap is needed to observe diffraction i light than in sound.

A

Light has a much smaller wavelength, so it does not diffract through such a large gap or obstacle.

29
Q

Why does polarisation mean?

A

Polarisation means that the particles oscillate along one direction only.

30
Q

What does it mean if a wave is plane polarised?

A

The ‘plane of oscillation’ contins the oscillation of the particles and the direction of travel of the wave.

31
Q

Explain why a longitudal wave cannot be plae polarised.

A

In longitudal waves, the oscillation are always parallel to the direction of energy transfer, so longitudal waves cannot be plane polarised. Their oscillations are already limited to only one plane. (The direction of energy)

32
Q

How can transverse waves become plane polarised?

A

When transverse waves reflect off a surface they become partially polarised. This means there are more waves oscillating in one particular plane, but the wave is not completely plane polarised.

33
Q

How is the intensity of a wave defined?

A

The intensity of a progressive wave is defined as the radiant power passing through a surface per unit area.

34
Q

How is the intensity of a wave calculated. Define terms and include units.

A

The intensity of a progressive wave is defined as the radiant power passing through a surface per unit area. Intensity has units watters per square metre. (Wm^-2)

35
Q

Explain why the intesity of a wave reduces as it spreads out from a point source.

A

When the travels out from a source the radiant power spreads out, reducing intensity.

36
Q

What happens to intensity if distance doubles?

A

decreases intensity by factor of four.

37
Q

Is an electromagnetic wave transverse or longitudinal?

A

An EM wave is an example of a transverse wave, but is a little more complex than ripple on a pond.

38
Q

What is a unique property of electromagnetic waves that allows energy to be transferred from Sun to Earth?

A

Electromagnetic waves do not need a medium. Unlike all other waves, they can travel through a vaccum. Without this ability to travel through space there could be no life on Earth, because this is how energy is transferred to our planet from the Sun.

39
Q

How and X-rays and Gamma Rays classified?

A

The wavelength ranges of X-rays and Gamma Rays overlap. Unlike other parts of the spectrum, these EM waves are not classified by their wavelength, but by their origin. X-rays are emitted by fast moving electrons whereas gamma rays come from unstable atomic nucleus.

40
Q

List the key properties of all EM waves.

A

Like all waves, EM waves can be reflected, refracted, and diffracted. As EM waves are transverse waves, they can be plane polarised.

41
Q

What does it mean if light is unpolarised?

A

Unpolarised light waves are light waves in which the vibrations occur in more than a singular plane.

42
Q

What does it mean if light is polarised?

A

Polarised light waves are light waves in which vibrations occur in a single plane.

43
Q

How is refractive index calculated?

A

Refactive index (n) = Speed of light in vaccum (c) over Speed of light through material (ms^-1)

44
Q

What does it mean if a material has a refractive index, n, equal to one?

A

If n = 1 then the speed of light through the material is the same as the speed of light through a vaccum.

45
Q

State the law of refraction.

A

Refractive index of material (n) multiplied by Sin theta (sin0) = constant (k)

46
Q

What is total internal refraction?

A

The total internal reflection of light occurs at the boundary between two different media.

47
Q

State the two conditions required for total internal reflection to occur?

A
  1. The light must be travelling through a medium with a higher refractive index as it strikes the boundaries with a lower refractive index. For example, total internal reflection is possible when light in glass meets air, but not the other way around.
  2. The angle at which the light strikes the boundary must be above the critical angle. This angle depends on the refractive index of the medium.
48
Q
A

Physics (8 decks)

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