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Physics Igcse > P4 > Flashcards

P4 Flashcards

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1
Q

What is a wave?

A

An oscillation or vibration about a fixed point
Only transfers energy/information not matter

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2
Q

Describe the properties of transverse waves

A

Movement of energy -> forward/backward
Vibration -> up/down
They are perpendicular to each other

Can move through solids, surfaces of liquids but not inside liquids/gases
(but em waves can (also only ones that can travel in a vacuum))

Constant density
Constant pressure

Examples:
Water ripples
Vibrating string
Em waves

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3
Q

Describe the properties of longitudinal waves

A

Movement of energy -> forward/backward
Vibration -> forward/backward
They are parallel to each other

Can move through solids, liquids and gases but cannot travel in a vacuum (needs a medium to travel through)

Changes in density
Changes in pressure

Examples:
Sound

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4
Q

How can frequency, wavelength and wave speed be seen in a ripple tank?
(Basically the equation for each one)

A

Frequency:
Time for a give # of waves to pass / time taken

Wavelength:
Length of screen / # of wavefronts

Wave speed:
Frequency x wavelength

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5
Q

What is a wavefront? (How do they help find the wavelength?)

A

Each wavefront is a single wave
(Represented as a line and arrow denoting direction)

The space between each line is the wavelength

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6
Q

Define crest and trough

A

Crest/peak:
The highest point on a wave above the ‘rest’

Trough:
The lowest point on a wave below the ‘rest’

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7
Q

Define amplitude (including its symbol and the unit of measurement)

A

The distance from the undisturbed position (rest) to the peak or trough of a wave
-> the min/max displacement from the undisturbed position

Symbol: A
Measured in: meters

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8
Q

Define wavelength (including its symbol and the unit of measurement)

A

The distance from one point on the wave to the same point on the next wave

Transverse: peak to peak
Longitudinal: start of compression time start of compression

Symbol: lambda (λ)
Measured in: meters

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9
Q

Define frequency (including its symbol and the unit of measurement)

A

The number of waves passing a point in a second

Symbol: f
Measured in: Hertz (Hz)

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10
Q

Define wave speed (including its symbol and the unit of measurement)

A

The speed at which energy is transferred through a medium
-> distance travelled/second

Symbol: v
Measured in: meters/second (m/s)

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11
Q

Define reflection

A

When a wave hits a boundary between two media and doesn’t pass though, it instead stays in the original medium

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12
Q

What is the law of reflection?

A

Angle of incidence (i) = angle of reflection (r)

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13
Q

Define refraction

A

When a wave enters a different medium, their speed can change
Refraction occurs when a wave passes a boundary between 2 different transparent media

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14
Q

Which characteristics of a wave stays the same when refracted?
Wavelength
Direction
Frequency

A

Frequency is the only one that stays the same

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15
Q

Which direction will the wave go when it slows of speeds up? What does this do to the wavelength?

A

Wave slows -> waves bunch together -> shorter wavelength
Towards the normal

Wave speeds -> wave spread -> longer wavelength
Away from normal

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16
Q

Define diffraction

A

When waves pass through a narrow gap, the wave spreads out

As the gap becomes bigger the effect is less pronounced
It also happens on edges

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17
Q

What is the equation for wave speed?

A

Frequency x wavelength

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18
Q

What is refraction caused by?

A

A change in speed

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19
Q

How can refraction be shown in a ripple tank?

A

Place a glass block in the tank below the surface
-> partially covers the floor

As speed depends on depth the ripples slow over the block (shallower)

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20
Q

What is a normal?

A

The normal is an imaginary line that is 90° to the boundary

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21
Q

What are the characteristic of the image created by a plane mirror?

A

Same size as object

Same distance behind the mirror as the object is in front of the mirror
-> in line with the object

Virtual
-> cannot be projected onto a screen usually appearing to be behind the lens

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22
Q

How do the rays relate to the place where the virtual image will form?

A

Where the virtual rays converge

23
Q

Explain an experiment that can be done to investigate reflection by plane mirrors

A

Aim:
Investigate reflection by a plane mirror

Variables:
Independent -> angle of incidence
Dependent -> angle of reflection
Control -> distance of ray box from mirror, width of beam, wavelength+frequency of light

Materials:
Ray box
Plane mirror (+stand)
Protractor

Method:
>middle of paper make 10cm line
>use protractor make 90° line that bisects 10cm line
>place mirror on first line
>switch ray box on -> aim at cross section of the two lines
>mark 2 postions: one on incident ray one on reflected ray
>remove/turn off box and mirror
>use ruler to join 2 points to where the cross section is
>use protractor to measure i and r
>repeat and make a table

Result:
Law of reflection observed

Revaluation:
Errors:
90° line not correct
Mirror distorted
Points marked inaccurately
Protractor resolution

Safety:
Ray box -> could cause burns/eye damage
Liquids + electrical/paper
Mirror damage

24
Q

What is the equation for the refractive index?

A

Refractive index = speed of light in vacuum/speed of light in material

Always 1<

25
Q

Relate the change in direction (refraction) of light to the density of media

A

Less dense to more dense -> towards normal
r < i

More dense to less dense -> away from normal
r > i

Along normal -> no change

26
Q

What is total internal reflection?

A

Sometimes when light goes from denser -> less dense instead of being refracted light is reflected

When: i > critical angle

27
Q

Where is TIR used?

A

Prisms (optical instruments)
Periscopes
Binoculars
Telescopes
Cameras

Safety reflectors:
Bikes
Cars road signs

Also optical fibers

28
Q

What is the critical angle?

A

When r = 90° light is refracted along the boundary

i when r=90° is known as the critical angle

29
Q

How do optical fibers work? How are optical fibers used?

A

> light travelling down the fiber is internally reflected

Communication:
The wave carries information

Medicine:
> used to see inside the human body
Light from light source goes through optical fiber -> objective lens -> reflected from object -> into eyepiece lens (image created)

30
Q

Describe the action of a thin converging lens (convex)

A

Parallel rays are brought to a focus
> represented by line with arrow on both ends

Focal length is determined buy the curviness of the lens
More curve = small length

31
Q

Describe the action of a thin diverging lens (concave)

A

Parallel rays are made to diverge from one point
Represented by: a line with reverse arrows on both ends

32
Q

Define principal focus/focal point

A

The point at which rays of light travelling parallel to the principal axis:
> intersect the principal axis and converge
OR
> the point where the rays appear to diverge from

33
Q

Define focal length

A

The distance between the center of the lens and the principal focus

34
Q

Define real image

A

An image that is formed when the light rays from an object converge and meet each other and can be projected onto a screen

Always convergence towards focus
Always inverted

35
Q

Define virtual image

A

An image that is formed when the light rays from an object do not meet but appear to meet behind the lens and cannot be projected onto a screen

Always divergence from a point
Always upright

36
Q

Explain how you can find the location of a real image created by a converging lens

A
  1. Draw a ray from the top of the object through the center of the lens
  2. Draw a ray from the top of the object travelling parallel to principal axis when ray emerges it will travel directly towards focal point
  3. Where the rays converge -> position of image
    -> REMEMBER -> ALWAYS INVERTED
37
Q

T or F:
Both converging lenses and diverging lenses can only create real images

A

F

Converging can create both
Diverging can only create virtual

38
Q

How is the characteristics image change depending on the objects distance from the lens?

A

f (focal distance)

2f -> same size image

2f< -> diminished image

f < x < 2f -> enlarged image

Upright -> virtual
Inverted -> real

39
Q

How can a convex lens be used as a magnifying glass?

A

> if the object is placed closer to the lens than the focal length the emerging ray diverges -> it is now a VIRTUAL IMAGE

The point is found by extending rays backwards -> creating virtual rays
-> virtual image found where the rays cross
—>virtual, enlarged, upright

For use as a magnifying glass -> must be held close to face

40
Q

How is sound produced?

A

Sound waves are produced by vibrating sources
When a sound waves comes into contact with a solid vibrations are transferred

Ex: opera singer and crystal glass

41
Q

What type of wave is a sound wave?

A

Longitudinal wave
-> Needs a medium to travel through
-> parallel energy transfer and vibration

42
Q

Define compression

A

A region of higher density (molecules are bunched together)

43
Q

Define rarefaction

A

A region of lower density (molecules spread out)

44
Q

T of F: rarefaction and compression do cause a change in pressure

A

T

This makes sound a pressure wave
When wave hits solid -> variation in pressure causes surface to vibrate (in sync)

45
Q

What is the range of audible frequencies for a healthy human ear?

A

20 Hz to 20,000 Hz

46
Q

T or F

Sound waves do not need a medium to travel through

A

F

47
Q

What is the speed of sound in air? How does temperature affect this?

A

Speed of sound in air -> 340 m/s in room temp

High temp -> faster sound
Varies from 330-350 m/s

48
Q

Describe an experiment to determine the speed of sound in air

METHOD 1: MEASURING SOUND BETWEEN TWO POINTS

A
  1. 2 people stand around 100m apart -> distance measured by trundle wheel
  2. 1st person -> 2 wooden block which they bang above their head
  3. 2nd person has stop watch -> starts when see bang block -> stop when sound heard
  4. Repeat and find the average

Speed of sound: distance traveled/time taken

49
Q

Describe an experiment to determine the speed of sound in air

METHOD 2: USING ECHOS

A
  1. Person 1 stands around 50m from a wall (use trundle wheel to measure distance)
  2. person 1 bangs 2 wooden bocks together
  3. Person 2 has stopwatch -> starts when hear clap -> stop when hear echo
  4. Repeat and average

Speed of sound = 2 x distance to the wall / time taken

50
Q

Describe an experiment to determine the speed of sound in air

METHOD 3: USING AN OSCILLOSCOPE

A
  1. 2 microphones are connected to oscilloscope and placed around 5 m apart (use tape measure)
  2. Oscilloscope set so it’s triggered when 1st microphone detects sound
    -> adjust time base -> sound in both microphones can be seen
  3. 2 wooden block clapped next to 1st microphone
  4. Oscilloscope used to determine time between the 2 microphones
  5. Repeat then average

Speed of sound = distance between microphones / time between peaks

51
Q

Order solids, liquids and gases in the order of which medium sound travels through fastest (+ why)

A

Gas < liquid < solid

Molecules are closer together

52
Q

What characteristics of waves related to loudness and pitch?

A

Frequency = pitch
> high pitch -> high frequency
> low pitch -> low frequency

Amplitude = volume/loudness
> large amplitude -> high volume
> small amplitude -> low volume

53
Q

What is an echo?

A

The reflection of sound of off a hard surface

54
Q

How are echos used?

A

Used to measure depth/detect objects (usually in the ocean)
> sound waves transmitted from surface
> sound waves reflect off the bottom of the ocean
> time take -> used to calculate depth

> length wave travelled = x2 the depth of the ocean

Physics Igcse (9 decks)

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