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Light - Wave or Photon?
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Questions in this quiz (20)
1Photons:
- A photon is a [blank_start]quantum[blank_end] of e[blank_start]lectromagnetic[blank_end] r[blank_start]adiation[blank_end].
- EM waves can only be released in [blank_start]discrete[blank_end] packets called q[blank_start]uanta[blank_end]. The energy carried by one of these wave-packets (i.e. energy of a photon) is E = hf where E is p[blank_start]hoton[blank_end] [blank_start]energy[blank_end] (J), h is [blank_start]Planck's[blank_end] [blank_start]constant[blank_end] (6.63 x 10^-34) and f is [blank_start]frequency[blank_end] (Hz).
- Therefore the higher the frequency of the EM radiation, the [blank_start]more[blank_end] energy the photons carry.
- A photon acts as a [blank_start]particle[blank_end], and will either transfer [blank_start]all[blank_end] or [blank_start]none[blank_end] of its energy when interacting with another particle, e.g. an [blank_start]electron[blank_end].
- Photons have [blank_start]no[blank_end] charge. They are [blank_start]neutral[blank_end], like neutrons.
- Aquantum
- Blectromagnetic
- Cadiation
- Ddiscrete
- Ehoton
- Fenergy
- GPlanck's
- Hconstant
- Ifrequency
- Jmore
- Kparticle
- Lall
- Mnone
- Nelectron
- Ono
- Pneutral
- Quanta
2What is special about photons which have wavelengths between about 400 and 700 nanometres (nm)?
- AThey trigger receptors in our retinas (we can see them).
- BThey trigger receptors in our retinas (we can't see them).
3The electron-volt (eV) is a unit of [blank_start]energy[blank_end] used for the very [blank_start]small[blank_end] amounts of energy possessed by particles such as e[blank_start]lectrons[blank_end] or p[blank_start]hotons[blank_end].
It is defined as:
The kinetic energy [blank_start]gained[blank_end] by an electron after it has been [blank_start]accelerated[blank_end] through a [blank_start]potential[blank_end] [blank_start]difference[blank_end] of 1 volt.
Therefore 1 eV = [blank_start]e[blank_end] x [blank_start]V[blank_end] = 1.60 x 10^-19 x 1 = 1.60 x 10^-19 J.
e = size of [blank_start]charge[blank_end] on an electron = 1.60 x 10^-19 C
When the electron is accelerated through a potential difference, it transfers some [blank_start]electrical[blank_end] [blank_start]potential[blank_end] energy (eV) into [blank_start]kinetic[blank_end] energy (eV = 1/2mv^2).
- Aenergy
- Bsmall
- Clectrons
- Dhotons
- Egained
- Faccelerated
- Gpotential
- Hdifference
- Ie
- JV
- Kcharge
- Lelectrical
- Mpotential
- Nkinetic
4E eV = E J / 1.60 x 10^-19 and EJ = hf
=> E eV = hf / 1.60 x 10^-19
=> E eV = hc / λ(1.60 x 10^-19)
Therefore:- AE eV ∝ 1 / λ
- BE eV ∝ λ
- CE J ∝ 1 / λ
- DE eV ∝ f
5Quanta:
A quantum is the [blank_start]smallest[blank_end] possible amount of something, i.e. a quantum [blank_start]cannot[blank_end] be subdivided. Anything which is quantized exists in [blank_start]discrete[blank_end] amounts, i.e. we cannot have fractions of an amount.
A photon is a quantum because for a given frequency/wavelength, you cannot have a [blank_start]smaller[blank_end] amount of energy than the [blank_start]one photon[blank_end] - discrete amounts only.
- Asmallest
- Blargest
- Ccannot
- Dcan
- Ediscrete
- Fcontinuous
- Gsmaller
- Hlarger
- Ione photon
- Jone electron
6Excitation:
1. The atom [blank_start]gains[blank_end] [blank_start]energy[blank_end] (e.g. by being [blank_start]hit[blank_end] by another particle or by being [blank_start]shaken[blank_end] by another atom such as when a material is [blank_start]heated[blank_end]).
2. Electrons can become [blank_start]excited[blank_end] - they move to [blank_start]higher[blank_end] [blank_start]energy levels[blank_end] ([blank_start]outer[blank_end] electrons only).
3. Excited electrons will [blank_start]quickly[blank_end] move back down to a [blank_start]lower[blank_end] energy level, and eventually back to the [blank_start]ground state[blank_end]. To do this they must [blank_start]lose[blank_end] energy which they do by emitting a [blank_start]photon[blank_end]: [blank_start]one[blank_end] photon for each transition. This process is known as [blank_start]de-excitation[blank_end] of the atom.
- Agains
- Benergy
- Chit
- Dshaken
- Eheated
- Fexcited
- Ghigher
- Henergy levels
- Iouter
- Jinner
- Kquickly
- Lslowly
- Mlower
- Nground state
- Olose
- Pgain
- Qphoton
- Rde-excitation
- Sone
7Energy Levels:
- An energy level is a [blank_start]discrete[blank_end] quantity of energy for an [blank_start]electron[blank_end] in an atom. The electrons in an atom can only [blank_start]exist[blank_end] in these well-defined energy levels.
- Electrons can move [blank_start]down[blank_end] energy levels by emitting a [blank_start]photon[blank_end] (one per transition).
- The energy carried by each photon is equal to the [blank_start]difference[blank_end] in energies between the two levels. ΔE = [blank_start]E2 - E1[blank_end] = hf.
- Electrons exist in discrete energy levels so only certain [blank_start]energy changes[blank_end] are possible meaning only certain amounts of energy can be [blank_start]released[blank_end]. As E = hf, this also means that only certain [blank_start]frequencies[blank_end] of radiation are emitted (h is constant so for particular E's there are particular f's).
- Electrons can also move [blank_start]up[blank_end] energy levels if they [blank_start]absorb[blank_end] a photon with the [blank_start]exact energy difference[blank_end] between the two levels. The movement of an electron to a [blank_start]higher[blank_end] energy level is called [blank_start]excitation[blank_end].
- Each energy level is given a number, with n = 1 representing the [blank_start]ground[blank_end] state. The ground state is where the [blank_start]outermost[blank_end] electron is at the start.
- Adiscrete
- Belectron
- Cexist
- Ddown
- Eup
- Fphoton
- Gdifference
- HE2 - E1
- IE1- E2
- Jenergy changes
- Kreleased
- Lfrequencies
- Mabsorb
- Nexact energy difference
- Oexcitation
- Phigher
- Qlower
- Rground
- Soutermost
- Tinnermost
8Excited mercury atoms emit ultraviolet radiation. The phosphor coating then absorbs the UV and emits visible light. Why does the phosphor coating emit different wavelengths from the mercury?
- APhosphor has different energy levels to mercury so it has different energy changes when it de-excites resulting in different frequencies and hence different wavelengths of light being emitted.
- BPhosphor has different energy levels to mercury so it has different energy changes when it de-excites resulting in different frequencies and hence the same wavelengths of light being emitted.
9Describe the emission of the lowest frequency photon possible for an excited atom with these energy levels and calculate its frequency.
A photon is emitted when an [blank_start]electron[blank_end] moves to a [blank_start]lower[blank_end] energy level. The lowest [blank_start]frequency[blank_end] photon will be [blank_start]emitted[blank_end] for a transition from level [blank_start]5[blank_end] to level [blank_start]4[blank_end].
- A5
- B4
- Clower
- Delectron
- Efrequency
- Femitted
10There are many different transitions an excited electron can make depending on how many energy levels it moves down and where it started. This results in many different frequencies of photons being released.
- ATrue
- BFalse
11Why are the energies shown as negative?
Because when an electron reaches n = ∞ it is [blank_start]no longer[blank_end] part of the atom so has an electrical potential energy (eV) defined as [blank_start]zero[blank_end]. n = ∞ must be at a [blank_start]higher[blank_end] energy level than the other levels because electrons need to [blank_start]gain[blank_end] energy to attain this state so the lower energy levels must therefore be [blank_start]below[blank_end] zero and hence [blank_start]negative[blank_end].
- Ano longer
- Bstill
- Czero
- D∞
- Ehigher
- Flower
- Ggain
- Hlose
- Ibelow
- Jabove
- Knegative
- Lpositive
12Identifying Gases:
- A sample of gas is bombarded with [blank_start]electrons[blank_end] so atoms of the gas excite and [blank_start]de[blank_end]-[blank_start]excite[blank_end], emitting [blank_start]visible[blank_end] light.
- This visible light emitted from the gas can then be passed through a [blank_start]diffraction[blank_end] [blank_start]grating[blank_end] to split it into its different colours.
- The type of pattern produced in this way is called a [blank_start]line[blank_end] [blank_start]emission[blank_end] [blank_start]spectrum[blank_end].
- A [blank_start]spectrometer[blank_end] is used to view this pattern and determine the [blank_start]angles[blank_end] of the coloured beams.
- The equation [blank_start]n[blank_end]λ = d[blank_start]sin[blank_end]θ can be used to find the angle.
- Because each element has its own c[blank_start]haracteristic[blank_end] line emission spectrum, we can identify the composition of an unknown gas by c[blank_start]omparing[blank_end] its spectrum with k[blank_start]nown[blank_end] spectra. We can even detect the presence of c[blank_start]ompounds[blank_end] (e.g. carbon dioxide) in the same way.
- Aelectrons
- Bvisible
- Cdiffraction
- Dexcite
- Egrating
- Fde
- Gline
- Hemission
- Ispectrum
- Jspectrometer
- Kangles
- Ln
- Msin
- Nharacteristic
- Oomparing
- Pnown
- Qompounds
13Hot Gases Produce Line [blank_start]Emission[blank_end] Spectra:
- If you heat a gas to a [blank_start]high[blank_end] temperature, the atoms become [blank_start]excited[blank_end] (one or more of their electrons is moved to a higher [blank_start]energy level[blank_end]).
- As electrons within the atom fall back to the [blank_start]lower[blank_end] energy levels, they emit energy as [blank_start]photons[blank_end].
- If you split the light from a hot gas with a prism or a diffraction grating, you get a line [blank_start]emission[blank_end] spectrum.
- A line emission spectrum is seen as a series of [blank_start]bright[blank_end] lines against a [blank_start]black[blank_end] background.
- Each line on the spectrum corresponds to a particular [blank_start]wavelength[blank_end] of light emitted by the source. Since only certain photon energies are [blank_start]allowed[blank_end], you only see the [blank_start]corresponding[blank_end] wavelengths (E = hf = hc / λ).
- Knowing the photons' wavelengths means you can work out their [blank_start]energies[blank_end] and hence the [blank_start]energy levels[blank_end] of the atoms. This allows you to [blank_start]identify[blank_end] gases and gaseous compounds.
- AEmission
- BAbsorption
- Chigh
- Dexcited
- Eenergy level
- Flower
- Gphotons
- Hemission
- Ibright
- Jblack
- Kwavelength
- Lfrequency
- Mallowed
- Ncorresponding
- Oenergies
- Penergy levels
- Qidentify
14Cool Gases Produce Line [blank_start]Absorption[blank_end] Spectra:
- You get a line absorption spectrum when [blank_start]white[blank_end] light passes through a [blank_start]cool[blank_end] gas and then a [blank_start]diffraction grating[blank_end] or prism.
- At [blank_start]low[blank_end] temperatures, most of the electrons in the gas atoms will be in their [blank_start]ground states[blank_end].
- Photons of the correct wavelength are [blank_start]absorbed[blank_end] by the electrons to [blank_start]excite[blank_end] them to [blank_start]higher[blank_end] energy levels.
- These wavelengths are then [blank_start]missing[blank_end] from the [blank_start]continuous[blank_end] spectrum when it comes out the other side of the gas.
- You see a continuous spectrum with black lines in it [blank_start]corresponding[blank_end] to the absorbed wavelengths.
- If you compare the absorption and emission spectra of a particular gas, the [blank_start]black lines[blank_end] in the absorption spectrum match up to the [blank_start]bright lines[blank_end] in the emission spectrum.
- The dark lines represent [blank_start]wavelengths[blank_end] where an [blank_start]insignificant[blank_end] number of [blank_start]photons[blank_end] have arrived at the [blank_start]spectrometer[blank_end]. They are the photons which have been absorbed by the cooler [blank_start]less dense[blank_end] gas atoms when they were excited.
- Different gases absorb [blank_start]different[blank_end] wavelengths of light because they have different [blank_start]energy levels[blank_end]. Therefore the dark lines are at [blank_start]specific wavelengths[blank_end] for specific elements and can tell you what cool gas the light [blank_start]passed[blank_end] through.
- AAbsorption
- BEmission
- Cwhite
- Dcool
- Ehot
- Fdiffraction grating
- Glow
- Hground states
- Iabsorbed
- Jexcite
- Khigher
- Lmissing
- Mcontinuous
- Ncorresponding
- Oblack lines
- Pbright lines
- Qwavelengths
- Rinsignificant
- Sphotons
- Tspectrometer
- Uless dense
- Vmore dense
- Wdifferent
- Xthe same
- Yenergy levels
- Zspecific wavelengths
- AApassed
15Finding the emission spectrum:
Emission spectrum = [blank_start]Continuous[blank_end] spectrum [blank_start]-[blank_end] [blank_start]Absorption[blank_end] spectrum
You can then m[blank_start]atch[blank_end] the emission spectrum of the star to the emission spectrum of a g[blank_start]as[blank_end] using k[blank_start]nown[blank_end] emission spectra in the l[blank_start]ab[blank_end].
- AContinuous
- B-
- CAbsorption
- Datch
- Eas
- Fnown
- Gab
16Finding elements in a star:
If [blank_start]all[blank_end] the dark lines of the element feature in the star's line [blank_start]absorption[blank_end] spectra, then that element is [blank_start]present[blank_end] in the star.
e.g. Helium and [blank_start]Hydrogen[blank_end] are the only gases listed which are present in Spectra A.
- Aall
- Babsorption
- Cpresent
- DHydrogen
17How does helium in the Sun's atmosphere cause a set of dark lines in the continuous spectrum?
- Photons of the c[blank_start]orrect[blank_end] w[blank_start]avelength[blank_end] from the Sun are [blank_start]absorbed[blank_end] by [blank_start]electrons[blank_end] in the helium atoms.
- The electrons are [blank_start]excited[blank_end] and move to a higher [blank_start]energy[blank_end] [blank_start]level[blank_end].
- As photon [blank_start]energy[blank_end] = d[blank_start]ifference[blank_end] in energy levels, only c[blank_start]ertain[blank_end] differences are possible between d[blank_start]iscrete[blank_end] energy levels so only photons with s[blank_start]pecific[blank_end] amounts of energy are [blank_start]absorbed[blank_end].
- This means there are specific photon e[blank_start]nergies[blank_end] and hence w[blank_start]avelengths[blank_end] [blank_start]missing[blank_end] from the continuous spectrum and they can be identified as helium by looking at the [blank_start]differences[blank_end] between helium's energy levels.
- Aabsorbed
- Belectrons
- Cexcited
- Denergy
- Elevel
- Forrect
- Gavelength
- Henergy
- Iertain
- Jiscrete
- Kpecific
- Labsorbed
- Mnergies
- Navelengths
- Omissing
- Pdifferences
- Qifference
18Fluorescence:
A material takes in a wavelength of non-[blank_start]visible[blank_end] light and gives out a wavelength of visible light.
e.g. in a fluorescent lamp, [blank_start]UV[blank_end] light from de-exciting mercury atoms is absorbed by a [blank_start]phosphor[blank_end] coating which gives out [blank_start]visible[blank_end] light as phosphor atoms [blank_start]excite[blank_end] and then [blank_start]de[blank_end]-[blank_start]excite[blank_end].
- Avisible
- BUV
- Cphosphor
- Dvisible
- Eexcite
- Fde
- Gexcite
19An atom can be excited if a material is heated but also by an incoming photon. There are two rules for photon and electron interaction:
- APhotons and electrons almost always only interact on a one to one basis.
- BIf a photon has energy E (where E =hf), then the amount of energy it can give to an electron is either all or zero.
- CPhotons and electrons almost always only interact on a two on two basis.
- DIf a photon has energy E (where E =hf), then the amount of energy it can give to an electron is as much as the electron needs.
20How can we use line absorption spectra to determine the motion of stars?
- Compare the pattern of lines to [blank_start]known[blank_end] [blank_start]normal[blank_end] [blank_start]positions[blank_end] of stars to see if they've moved.
- If the observed [blank_start]wavelengths[blank_end] of the lines [blank_start]increase[blank_end], then the star is [blank_start]moving away[blank_end].
- Therefore if the lines are shifted towards the [blank_start]red[blank_end] end of the spectrum then the star is moving [blank_start]away[blank_end].
- Aknown
- Bnormal
- Cpositions
- Dwavelengths
- Eincrease
- Fdecrease
- Gred
- Hblue
- Iaway
- Jmoving away
- Kcoming closer
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- AS - Level Sally's Physics (Waves and Particle Nature of Light) Quiz on Light - Wave or Photon?, created by Sally Lancaster on 22/04/2016.
- Author
- Sally Lancaster
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- English
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