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LC Physics > Light experiments > Flashcards

Light experiments Flashcards

1
Q

Focal length of concave mirror - Method

A
  • approx value of f found by…
  • set up as per diagram, distance from obj to mirror must be greater than approx f
  • move screen until image in sharpest focus
  • measure, using metre stick, image distance v from screen to pole of mirror + obj distance u from object to pole of mirror.
  • Repeat for diff values of u and v
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2
Q

Focal length of concave mirror - graph

A

x-axis: 1/u

y-axix: 1/v

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3
Q

Focal length of concave mirror - how to find approx value of f

A

by focusing on distant object onto screen. Distance from mirror to screen measured + taken as approx value of f

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4
Q

Verify Snell’s Law + measure refractive index of glass - method

A
  • place glass block on top of sheet of paper
  • draw outline of block
  • set up as shown
  • switch on ray box
  • track incident + emerging ray of the ray from ray box
  • remove block
  • join incident + emerging rays, draw normal ray
  • measure angle of incidence + angle of refraction using protractor
  • repeat for diff values of angle of incidence
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5
Q

Verify Snell’s Law + measure refractive index of glass - graph

A

x-axis: sin r

y-axix: sin i

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6
Q

refractive index of a liquid using real + apparent depth - method

A
  • set up as shown in diagram
  • adjust position + height of pin until image in mirror lines up with object pin in water, using no parallax method
  • measure d from object pin to top of water (real depth)
  • measure distance from pin to top of water (apparent depth)
  • repeat for diff containers of diff depths
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7
Q

measure focal length of converging lens - method

A
  • approx value of f found by…
  • set up as per diagram, distance from obj to lens greater than approx f
  • move screen until image at its sharpest
  • measure, using metre stick, image distance v from screen to centre of lens + obj distance u from object to centre of lengs
  • repeat for diff values of u and v
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8
Q

measure focal length of converging lens - graph

A

x-axis: 1/u

y-axis: 1/v

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9
Q

wavelength of monochromatic light - method

A
  • monochromatic light source: laser
  • set up as per diagram in a dark room with laser shining onto screen
  • place diffraction grating in front of laser
  • first order images located by..
  • measure, using metre stick, distance from central image to two first order images
  • find angle by…
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10
Q

wavelength of monochromatic light - how first order images located

A
  • find central image/zero order image of beam (beam that goes straight thru diff grating, image observed when no grating was present)
  • look for beams to either side of central line
  • these are the first order images
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11
Q

wavelength of monochromatic light - ways of finding angle

A
  • angle of first order image measured using protractor
  • measure angle of second + third order images (if visible)

OR

  • measure distance (d) from grating to screen
  • measure distance (x) from central image to other images
  • find angle using tanΘ = x/d
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12
Q

Verify Snell’s Law + measure refractive index of glass - relationship shown on graph + show graph verifies it

A

Sin i ∝ SIn r

-straight line through origin verifies Snell’s Law, that Sin i ∝ SIn r

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13
Q

Verify Snell’s Law + measure refractive index of glass - how to use graph to get refractive index

A
  • get slope of the line

- slope = y2-y1/x2-x1

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14
Q

Verify Snell’s Law + measure refractive index of glass - what would be observed if the incident ray was perpendicular to the block?

A

-ray passes straight through

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15
Q

Verify Snell’s Law + measure refractive index of glass - why is using a graph more accurate than calculating for each pair of angles and finding the mean?

A
  • outliers can be identified

- slope gives weighted mean

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16
Q

Verify Snell’s Law + measure refractive index of glass - smallest angle of incidence

A

20°

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17
Q

Verify Snell’s Law + measure refractive index of glass - why smaller values lead to a less accurate result?

A

-greater percentage error (smaller angles would be difficult to measure + would have small sine values, leading to higher percentage error)

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18
Q

Verify Snell’s Law + measure refractive index of glass - sources of error

A
  • small angles

- when deciding upon the exact value of angles using the protractor

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19
Q

Verify Snell’s Law + measure refractive index of glass - calculating refractive index

A
  • average value of sin i/sin r

- slope of line on graph

20
Q

focal length of converging lens - why it’s difficult to measure image distance accurately

A
  • difficult to locate sharp image

- difficult to locate centre of lens

21
Q

focal length of converging lens - finding value of focal length using data in table

A
  • state formula
  • find f for each set of values
  • find average f
22
Q

focal length of converging lens - why difficult to measure image distance when object distance less than 10cm

A
  • object inside focal point
  • image is virtual
  • image cannot be formed on a screen
23
Q

focal length of converging lens - precautions when measuring image distance

A
  • measure from centre of lens to screen
  • avoid parallax error
  • check for zero error on metre rule
  • measure perpendicular distance as if there are angles involved, they need to be factored into calculations
24
Q

focal length of converging lens - relationship from graph

A

the equation 1/u + 1/v = 1/f sums up the relationship between the focal length f, the object distance u and the image distance v.

25
Q

focal length of concave mirror - precautions when measuring image d

A
  • measure from centre/pole of mirror
  • avoid parallax mirror
  • ensure image is at its sharpest
  • have both screen and mirror vertical
26
Q

focal length of concave mirror - why unable to form image on screen when object close to mirror

A
  • object inside focal length
  • virtual image formed
  • image cannot be seen on a screen
27
Q

focal length of concave mirror - advantage of finding approx value for focal length

A
  • avoid placing object inside focal length

- to indicate magnitude of final answer for f

28
Q

focal length of concave mirror - focal length using graph?

A

-values where the line cuts the two axes are equal to 1/f, find the average of the two values where the axes are cut

29
Q

wavelength of monochromatic light - calculating wavelength of beam of light

A

nλ = dsinθ

30
Q

wavelength of monochromatic light - effect if diffraction grating of less lines used

A
  • angle decreases

- images closer together

31
Q

wavelength of monochromatic light - which grating would have a more accurate value for wavelength?

A
  • grating with more lines per mm

- larger measurements give smaller percentage error

32
Q

wavelength of monochromatic light - what if white light was used instead of monochromatic light?

A

-spectrum of white light observed / spectrum formed

33
Q

wavelength of monochromatic light - max no. of images that could be observed

A
  • use formula

- times by two and add one to account for central image and other side

34
Q

wavelength of monochromatic light - effect if wavelength decreased

A

-images closer together

35
Q

wavelength of monochromatic light - how beam of light produced

A

-laster

36
Q

wavelength of monochromatic light - which of the angles is the most accurate?

A
  • greatest angle

- largest angle gives smallest percentage error

37
Q

wavelength of monochromatic light - effect on increasing no. of lines per mm

A
  • larger angles

- images more spread out

38
Q

wavelength of monochromatic light - effect of having a longer wavelength

A
  • images more spread out

- larger angles

39
Q

wavelength of monochromatic light - how narrow beam of light produced

A

-use a laser

40
Q

wavelength of monochromatic light - how more lines per mm leads to more accurate result

A
  • greater angle

- smaller percentage error

41
Q

wavelength of monochromatic light - way of improving accuracy

A
  • increase distance or wavelength for smaller percentage error
  • find n for diff order images and find average
42
Q

wavelength of monochromatic light - note on angle

A

-read question carefully, if it says “angle between second order image to left and to right measured” make sure to divide the angle by two when doing calculations!!

43
Q

real and apparent depth - sources of error

A
  • deciding on exact location of position with no parallax

- measuring distances with metre stick

44
Q

monochromatic light - sources of error

A
  • angles on left and right might not be equal due to grating not being perpendicular to light source
  • using diff gratin with too few lines would lead to small angles + sine of angles, leading to greater percentage error
45
Q

“find the wavelength of light”

A

find wavelength using all of the data in the table and then find average wavelength!!!

LC Physics (25 decks)

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