optics

Question 1

what happens ti the ray if light when it is refracted?

Answer 1

it bends towards the normal when it passes into a more dense substance. away from the normal if it passes into a less dense substance.

Question 2

what is shells law?

Answer 2

when using glass, the angle of refraction is always less than the angle of incidence
the ratio of sini/sinr is the same for each light ray, this ratio is known as the refractive index.

Question 3

how do you calculate the refractive index?

Answer 3

sin i/sin r

C/Cs

Question 4

what is the calculation for smells law?

Answer 4

n1sinθ1=n2sinθ2

where θ1 = i and θ2 = r

Question 5

what are the conditions that usually have to occur for total internal reflection to take place?

Answer 5

the incident substance has to have a lager refractive index than the other.
the angle of incidence exceeds the critical angle.

Question 6

in optical fibres why must the core be narrow?

Answer 6

to prevent modal dispersion. this occurs in a wide core because light traveling along the axis of the core travels at a shorter distance per meter of fibre than light that repeatedly undergoes total internal reflection. a pulse sent out along a wide core would become longer than it ought to be, if it was too long it would merge with the next pulse.

Question 7

why are the fringes formed in the young’s double slit experiment?

Answer 7

due to the interference of light of the two slits:

where a bright fringe i formed, the light of one slit reinforces the light from the other slit -the light rays arrive in phase with each other

where a dark fringe is formed, the light from one slit cancels out the light from the other slit. the list rays drive 180 degrees out of phase.

Question 8

what is fringe separation?

Answer 8

the distance from the distance from the centre of a bright fringe to the centre of the next bright fringe. it depends on the slit separation, s, and the distance of the slits to the screen, D,

Question 9

what i the equation for fringe separation?

Answer 9

w= wavelength x D/s

Question 10

what does the fringe separation show?

Answer 10

the fringes become more widely spaced if:
the distance D from the slits to the screen is increased
the wavelength of light used is increased
the slit spacing is reduced. the slit spacing is the distance from the centre of the slit.

Question 11

what is the calculation for reinforcement at p?

Answer 11

the path difference s1p-s2p= m x wavelength

Question 12

what is the calculation for cancelation at p?

Answer 12

the path difference S1P-S2P = (m + 1/2) x wavelength

Question 13

why are double slits described as coherent sources?

Answer 13

they emit light of the same frequency and at constant phase difference. provided that we use the light from a laser, or with light from a narrow single slit if we are not using laser light.

Question 14

why can the light from two lamp bulbs not from an interference?

Answer 14

the light that is emitted from the bulbs is emitted at random meaning that the points of reinforcement and cancellation would change at random, so therefor no interference pattern id possible.

Question 15

what do the wavelengths of the light spectrum range from and to?

Answer 15

from red light - 650nm to violet light of around 350nm

Question 16

what type of light is laser light?

Answer 16

monochromic

Question 17

with a single slit pattern how can you widen then bring spacing?

Answer 17

increase the wavelength or make the single slit narrower.

Question 18

what is a defraction grating?

Answer 18

a diffraction grating is plate with many closely spaced parallel slits ruled on it.

Question 19

why is the light from the diffraction grating only transmitted in certain directions?

Answer 19

the light passing through each slit is diffracted.
the diffracted light waves from adjacent slits reinforce each other in certain directions only, including the incident light direction, and cancel out in all other directions.

Question 20

when using a diffraction grating what are the beams refered to as?

Answer 20

the central beam is referred to as the zero order beam (same direction as the incident beam) the other transmitted beams are numbered going outwards.

Question 21

when does the angle between the beams increase when testing a diffraction grating?

Answer 21

when light of a lower wavelength is used.

a grating with closer slits is used.

Question 22

what is the diffraction grating equation for the angle of diffraction of the nth order beam?

Answer 22

dsinθ=nλ

where d = the diffraction grating.

Question 23

how do you calculate the maximum number of orders?

Answer 23

d/λ rounded down to the nearest whole number.

Question 24

what are the different types of spectra?

Answer 24

continuous spectra
line emission spectra
line absorption spectra

Question 25

what is a line emission spectra?

Answer 25

the order of coloured vertical lines produced when an element emits light. the wavelengths of that light are characteristic of the chemical that produced them.