particles and waves (part 2)

Question 1

equation for energy of a photon

Answer 1

E=hf

Question 2

what is wave-particle duality?

Answer 2

light being observed as a wave or particle, depending on how we observe it

Question 3

how can electrons escape an atom?

Answer 3

by absorbing the minimum energy required, Eo (work function), and minimum frequency, fo (threshold frequency), from a photon of light

Question 4

how can we allow for more electrons to be released?

Answer 4

increasing irradiance of light source, as long as its above threshold frequency

Question 5

what is the work function?

Answer 5

the minimum energy required to release an electron from a surface

Question 6

what is the threshold frequency?

Answer 6

the minimum frequency of the photon of light that allows the electron to be released from an atom

Question 7

work function equation

Answer 7

Eo=hfo

Question 8

what is condition is required for the electron to have kinetic energy?

Answer 8

energy of photon must be greater than the work function- this extra energy would appear as kinetic energy

Question 9

equation for kinetic energy of an electron

Answer 9

Ek= E-Eo

Question 10

what is the photoelectric effect?

Answer 10

when light of a specific frequency falls on a metal plate and ejects electrons from its surface

Question 11

what evidence is there for the particle nature of light?

Answer 11

each photon removes one electron from surface

Question 12

what evidence is there for light being a wave?

Answer 12

phenomenon of interference of light

Question 13

when is interference observed?

Answer 13

when two waves with the same frequency and wavelength overlap

Question 14

what is the effect of interference dependant on?

Answer 14

whether the waves are in phase or out of phase

Question 15

what is constructive interference and when does it occur?

Answer 15

when two waves of equal amplitude meet in phase and combine to give a wave of twice the amplitude

when a wave crests coincide or wave troughs coincide

Question 16

3 things coherent waves share

Answer 16

same frequency, wavelength, and phase

Question 17

what is destructive interference and when does it occur?

Answer 17

when two waves of equal amplitude meet out of phase and combine to give a wave of zero amplitude

when a wave crest coincides with a wave trough

Question 18

what part of a water wave displays constructive interference?

Answer 18

bold lines moving outward from ripple

Question 19

what part of a water wave displays destructive interference?

Answer 19

faded gaps in between each section of lines

Question 20

example of the interference of light

Answer 20

youngs double slit experiment

monochromatic light shone through single slit producing a source of coherent waves

pass through a double slit to produce two coherent sources of waves

interference fringes produced on screen consisting of bands of bright light (constructive interference) and dark bands (destructive interference)

Question 21

what happens as frequency increases?

Answer 21

wavelength decreases

Question 22

maxima path difference equation

Answer 22

pd= nλ

Question 23

minima path difference equation

Answer 23

pd= (n+1/2)λ

Question 24

how does a grating work?

Answer 24

made up of many slits placed very close together

light passes through and depending on path difference to screen, a particular interference pattern is produced

Question 25

equation for wavelength of laser and fringe seperation

Answer 25

mλ= dsinθ

Question 26

equation for lines between slits

Answer 26

d= 1/lines per mm

Question 27

notation for nm

Answer 27

10^-9

Question 28

why is central maximum always white?

Answer 28

path difference to it is zero for all wavelengths or colours of light these superimpose on each other to produce white light

Question 29

what colour is always closest to central maxima

Answer 29

violet

Question 30

what is the refractive index?

Answer 30

the refractive index of a medium is the ratio of the speed of light in a vacuum to the speed of light in the medium (constant produced when plotting the sine of the angle of incidence against the sine of the angle of refraction)

Question 31

refractive index formula

Answer 31

n= sinθ1/sinθ2

Question 32

equation for snells law (full refractive index equation)

Answer 32

n2sinθ2 = n1sinθ1

Question 33

what does the refractive index measure?

Answer 33

the effect a medium has on light

Question 34

the greater the refractive index, the...

Answer 34

greater the change in speed and direction

Question 35

equating snells law, velocity, and wavelength

Answer 35

n2/n1 = sinθ1/sinθ2 = v1/v2 = λ1/λ2

Question 36

equating velocity and wavelength

Answer 36

v1/λ1 = v2/λ2

Question 37

what is irradiance?

Answer 37

the power per unit area (i.e. watts per square metres)

Question 38

irradiance formula

Answer 38

I= P/A

Question 39

irradiance units

Answer 39

wm^-2

Question 40

how to show the relationship between irradiance and distance

Answer 40

light meter measures light levels at a range of distances from the light bulb in an otherwise completely dark room

Question 41

what does a graph of irradiance against the inverse of squared distance prove?

Answer 41

irradiance is directly proportional to the inverse of the squared distance

Question 42

levels of irradiance with changing distance from source formula

Answer 42

i1d1² = i2d2² (i = k/d² ) (D(i1d1² = k))

Question 43

when can an electron move to a higher energy level?

Answer 43

if the electron gains energy but only at discrete energies

Question 44

difference between energy levels formula

Answer 44

E2-E1= hf

Question 45

what happens when an electron loses energy and moves to a lower level?

Answer 45

emits a photon

Question 46

what is seen in the line spectrum for sodium light?

Answer 46

two yellow lines that are close together, which are especially bright due to there being a lot of electrons making that energy jump, not because it is a large energy jump

Question 47

how can electrons move up energy levels?

Answer 47

absorb photons of light that contain the required amount of energy and a particular frequency since E= hf

Question 48

what happens when many electrons are making the same upward jump of energy levels?

Answer 48

a reduction in the number of photons with that energy level and of a particular frequency

Question 49

why are there missing lines in the emission spectrum of the sun?

Answer 49

gases present in the outer part of the sun absorb photons of particular frequencies absorption lines produced as a result correspond to the emission lines of particular elements- allowing identification of elements present in gas

Question 50

what is found when passing white light through an element in gaseous form?

Answer 50

results in dark bands appearing in the spectrum of white light two dark lines found where the bright yellow line emission spectrum are found