Light experiments

Question 1

Explain in the experiment Determine the wavelength of a beam of monochromatic light, how the angle between the first two images was obtained

Answer 1

Aim laser at screen so beam falls at right angles
place diffraction grating in light path at a right angle
Measure distance x from central image to other images
Measure D distance from grating straight to the screen.
Calculate theta with tan^-1 = x/D

Question 2

Describe how the student obtained v and u in the experiment to measure focal length of converging lens

Answer 2

Focus image of distant object onto screen to estimate f - measure an record distance from image to centre of lens for approx f
Set up apparatus with ray box a greater distance from lens than approx f
Adjust position of lens and screen relative to ray box until sharpest possible image is on screen
Measure and record from cross-wires to centre of lens- u
Measure and record screen to centre of lens-v
repeat procedure record several corresponding values for u and v

Question 3

Explain how to calculate focal length in the experiment to measure focal length of converging lens and in the experiment to measure Focal length of a concave mirror

Answer 3

use 1/f = 1/u + 1/v

calculate for each pair of values and calculate average

Question 4

Describe precautions when measuring the image distance in the experiment to measure focal length of converging lens

Answer 4

Avoid the error of parallax when measuring the image distance with metre stick
Avoid small values of u as smaller values result in greater percentage error
If possible determine sharpest image in the dark so eyes are more sensitive

Question 5

Why is it difficult to measure image distance when object is distance less than 10 cm
in the experiment to measure focal length of converging lens

Answer 5

Inside the focal length of lens and will produce a virtual image which cannot be formed on a screen

Question 6

Why is it difficult to measure image distance accurately in the experiment to measure focal length of converging lens

Answer 6

Difficult to locate sharpest image

Difficult to locate centre of lens

Question 7

Why would student not use values of i under 30 degrees? in the experiment to verify snells law

Answer 7

smaller values result in a greater percentage error

Question 8

Give two reasons why a graph is more accurate to find n then finding the mean in the experiment to verify snells law

Answer 8

This allows the outliers to be identifies
there is reference to the origin
Slope gives a weighted mean

Question 9

What happens if incident ray is perpendicular to block in the experiment to verify snells law

Answer 9

light goes straight through, no refraction occurs

Question 10

How do you use your graph to find n in the experiment to verify snells law

Answer 10

y2-y1/x2-x1

Question 11

Explain the relationship graphically between i and r and how a graph verifies this relationship in the experiment to verify snells law

Answer 11

plot sin i on y axis and sin r on x axis.

a straight line through the origin implies sin i is proportional to sin r which verifies relationship

Question 12

Describe with diagram how the angle of refraction was found in the experiment to verify snells law

Answer 12

Set up
Arrange for beam of light to pass from air into glass and exit other side
Draw outline of block onto paper
Draw lines corresponding to incident,refracted and emergent ray
Draw normal to block at POI
Measure and record i between normal and incident ray
Measure and record r between normal and refracted ray
Repeat to record several corresponding values for i and r

Question 13

Describe with diagram how the position of the image was found in the experiment to measure Focal length of a concave mirror

Answer 13

Find approx value for f by focusing an image of distant object on screen- distance from image to mirror should be measured and recorded as approx f.
Set up apparatus with object a greater distance than approx f from mirror
Adjust position of mirror and screen relative to ray box until sharpest image appears on screen
Measure and record cross-threads to pole of mirror as u and from image on screen to pole of mirror as v
Change u value and repeat the procedure to record several u and v values

Question 14

What is the advantage of finding the approximate focal length in the experiment to measure Focal length of a concave mirror

Answer 14

Avoid placing object in within the focal length during the experiment and not being able to find image on the screen

Question 15

Give two precautions when measuring image distance in the experiment to measure Focal length of a concave mirror

Answer 15

Measure from back of mirror
avoid error of parallax
Measure from centre of the mirror

Question 16

Describe how student could have found an approximate value for the focal length of mirror before the experiment in the experiment to measure Focal length of a concave mirror

Answer 16

Find approx value for f by focusing an image of distant object on screen- distance from image to mirror should be measured and recorded as approx f.

Question 17

How were first order images identified in the experiment to determine the wavelength of a beam of monochromatic light

Answer 17

They are directly to the left and right of the central line

Question 18

How was beam of light produced in the experiment to determine the wavelength of a beam of monochromatic light

Answer 18

Laser

Question 19

How was wavelength found in the experiment to determine the wavelength of a beam of monochromatic light

Answer 19

lamda= dsin(angle) / n

Question 20

How would you calculate the maximum number of images that appear on the screen in the experiment to determine the wavelength of a beam of monochromatic light

Answer 20

Max angle is put of 90degrees, find n using formula.

Max no of images (n max)x2+1

Question 21

What would the effect on the images be if gratings lines per mm decreased in the experiment to determine the wavelength of a beam of monochromatic light

Answer 21

They would be closer together

Question 22

What would happen to the positions of the images if the wavelength of light was decreased in the experiment to determine the wavelength of a beam of monochromatic light

Answer 22

They would be closer together

Question 23

What would student observe if monochromatic light was replaced with a source of white light? in the experiment to determine the wavelength of a beam of monochromatic light

Answer 23

A series of spectra

Question 24

How to make experiment more accurate in the experiment to determine the wavelength of a beam of monochromatic light

Answer 24

Repeat and get average value of wavelength from different orders
Increase D value

Question 25

Would 500mm or 80mm give a more accurate reading of wavelength and why in the experiment to determine the wavelength of a beam of monochromatic light

Answer 25

500mm because the angle of diffraction is bigger and there is less percentage error

Question 26

Explain method of experiment to find the refractive index of a liquid by measuring the real depth and apparent depth of an object in the liquid

Answer 26

Set up and ensure water touches mirror’s back
Look straight down
Adjust position of 2nd pin till it’s image is in line with image of 1st pin
Adjust 2nd pin’s height until there is no parallax between to images
Measure and record from object pin to top of beaker(depth of water) as real depth
Measure and record from search pin to back of mirror as apparent depth
Repeat at least four times using beakers of different lengths

Question 27

How is n calculated in experiment to find the refractive index of a liquid by measuring the real depth and apparent depth of an object in the liquid

Answer 27

real depth / apparent depth

Question 28

Where can errors arise in experiment to find the refractive index of a liquid by measuring the real depth and apparent depth of an object in the liquid

Answer 28

Locating position of no parallax
Avoid small values of real and apparent depths as small measurements lead to greater percentage errors
Avoid error of parallax measuring the real and apparent depth with metre stick