y12 long answer questions

Any three from points 1 to 6:

1.       Photon mentioned                                                                                          B1

2.       Surface electrons are involved                                                                       B1

3.       A single photon interacts with a single electron                                              B1

4.       Energy is conserved in the interaction between photon and electron             B1

5.       hf = f + KE(max)                                                                                            M1

6.       hf is the energy of the photon, f is the work function (energy) and
KE(max) is the (maximum) kinetic energy of the electron.                              A1

          The frequency of blue light is greater than the red light / the wavelength
of blue light is shorter than the red light    (ora)                                              B1

          The photon of blue light has energy greater than the work function energy
/ the frequency of blue light is greater than the threshold frequency (ora)     B1

Intensity does not change the energy of a photon                                          B1

QWC

The answer must involve physics, which attempts to answer the question.

Structure and organisation -

Award this mark if the whole answer is well structured.                                          B1

Spelling and Grammar mark -

          More than two spelling mistakes or more than two grammatical errors means
the SPAG mark is lost.                                                                                             B1

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7.       Electromagnetic waves - Any two from:                                                             B1 ´ 2

1.       EM wave / light behave like ‘particle’/ photon / quantum of energy

2.       E =hf / E = hc/l

3.       E is the energy of photon and f is the frequency (of EM waves) / l is
the wavelength

Moving electrons - Any four from:                                                           B1 ´ 4

4.       Moving / travelling particle / electron behaves like a wave

5.       Mention of the de Broglie (equation)

6.       l =

7.       l is the wavelength of particle/electron, m is the mass (of particle)
and v is speed

8.       Electrons can be diffracted     (Can score on diagram)

9.       Electrons travelling through matter /graphite (show diffraction effects)
(Can score on diagram if not scored in 8 above)

10.     Electrons diffract because their wavelength is comparable to the size of atoms

/gap between atoms                (Do not allow ‘particles in place of atoms)

QWC                                                                    Spelling, punctuation and grammar      B1

Organisation                                                                                         B1

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  8.     Maximum of 2 marks for correctly identifying the 4 errors OR stating the 2
correct notes:

i.e. errors in notes 1, 2, 3, and 6 (shown anywhere)                                                B2

{5 or 6 or 2 or 1 notes nominated scores ZERO, 4 correct scores 2, 3 correct scores 1}

Valid corrections score 1 mark each: do not allow “NOT” corrections apart
from note 3

Note 1: In longitudinal waves vibrations are parallel to wave direction (WTTE)     B1

          {OR in transverse waves vibrations are perpendicular to wave
direction (WTTE}

Note 2 light (or any of the em waves) can travel through a vacuum (WTTE)          B1

          {allow sound/longitudinal waves cannot travel thro’ a vacuum}

Note 3: waves carry energy/disturbance (not displacement or info)
            from…. (WTTE)                                                                                          B1

          {allow “waves do not carry the medium” and “the medium carries
the waves from…….”}

Note 6: wavelength = distance from crest to crest/trough to trough/max
           to max (WTTE)                                                                                            B1

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9.       With no current in the wire:
r.m.s.speed is square root of mean of squares of the speed of free electrons; (1)
r.m.s. speed depends on / increases with increasing temperature; (1)
free electrons move (fast) in random directions; (1)
colliding with atoms (in the lattice); (1)

          With current in the wire:
free electrons move in opposite direction to current / electric field; (1)
free electrons accelerate between collisions with atoms; (1)
this motion is superimposed on the random motion; (1)
Drift velocity is the mean value of electrons’ velocities due to this motion; (1)
value depending on current, cross-section of wire, free electron concentration
and electron charge / I, A, n and e. (1)                                                               max 7

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  10.   (a)     Maximum of five marks

Up to four from:

        /                                                                                      M1

All symbols (l, h, m and v or p) defined                                                       A1

Electrons travel / move / propagate (through space) as a wave                       B1

Electrons are diffracted / ‘spread out’                                                           M1

by the atoms / spacing between the atoms                                                     A1

The electrons are diffracted when their wavelength is less than or

comparable or same as size of atoms / gap between the atoms                      B1

Up to two from:

When the speed of electrons is increased) the rings ‘get smaller’                   B1

(At greater speed of electrons) the wavelength is shorter                               B1

(At greater speed of electrons) there is less diffraction                                  B1

QWC                 Organisation                                                                         B1

          Spelling, punctuation & grammar                                                B1

(b)     Electrons have mass / momentum / charge / can be ‘accelerated’                  B1

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