Light experiments Flashcards
(45 cards)
Focal length of concave mirror - Method
- 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
Focal length of concave mirror - graph
x-axis: 1/u
y-axix: 1/v
Focal length of concave mirror - how to find approx value of f
by focusing on distant object onto screen. Distance from mirror to screen measured + taken as approx value of f
Verify Snell’s Law + measure refractive index of glass - method
- 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
Verify Snell’s Law + measure refractive index of glass - graph
x-axis: sin r
y-axix: sin i
refractive index of a liquid using real + apparent depth - method
- 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
measure focal length of converging lens - method
- 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
measure focal length of converging lens - graph
x-axis: 1/u
y-axis: 1/v
wavelength of monochromatic light - method
- 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…
wavelength of monochromatic light - how first order images located
- 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
wavelength of monochromatic light - ways of finding angle
- 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
Verify Snell’s Law + measure refractive index of glass - relationship shown on graph + show graph verifies it
Sin i ∝ SIn r
-straight line through origin verifies Snell’s Law, that Sin i ∝ SIn r
Verify Snell’s Law + measure refractive index of glass - how to use graph to get refractive index
- get slope of the line
- slope = y2-y1/x2-x1
Verify Snell’s Law + measure refractive index of glass - what would be observed if the incident ray was perpendicular to the block?
-ray passes straight through
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?
- outliers can be identified
- slope gives weighted mean
Verify Snell’s Law + measure refractive index of glass - smallest angle of incidence
20°
Verify Snell’s Law + measure refractive index of glass - why smaller values lead to a less accurate result?
-greater percentage error (smaller angles would be difficult to measure + would have small sine values, leading to higher percentage error)
Verify Snell’s Law + measure refractive index of glass - sources of error
- small angles
- when deciding upon the exact value of angles using the protractor
Verify Snell’s Law + measure refractive index of glass - calculating refractive index
- average value of sin i/sin r
- slope of line on graph
focal length of converging lens - why it’s difficult to measure image distance accurately
- difficult to locate sharp image
- difficult to locate centre of lens
focal length of converging lens - finding value of focal length using data in table
- state formula
- find f for each set of values
- find average f
focal length of converging lens - why difficult to measure image distance when object distance less than 10cm
- object inside focal point
- image is virtual
- image cannot be formed on a screen
focal length of converging lens - precautions when measuring image distance
- 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
focal length of converging lens - relationship from graph
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.
