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Specific Objective 2.21 states: marked leniency
“discuss the nature of light as
electromagnetic radiation with
reference to its diffractive
properties”.
 The particulate nature of
light only comes in Unit 2
Module 3 [Atomic and Nuclear
Physics]:
 Specific
Objective1:“Particulate
nature of Electromagnetic
radiation”.
 Specific Objective1.8:
“discuss the photoelectric
effect as evidence for the
particulate nature of
Electromagnetic radiation”.

2c(i) “the distance across the four- Is it, “four-fringe”- bright fringes or dark?
fringe spacing was 3.6 mm”
Possible Solutions:
This statement is confusing.
Based on part 2(b): Show  If the statement means the distance [y4] from
th
that y = D/a where y = the central axis [n = 0] to the 4 bright
separation between the fringe [n = 4]: i.e. 4 spaces
central bright fringe [n = 0]  Either: y4 = 3.6 mm, ∴ y = y4/4 =3.6 mm /4
-3
and the first order fringe [n = 0.9 mm = 0.9 x10 m.
= 1] But y = D/a ∴ = ya/D = 6.3x10 m
-7
The statement probably means  Or: y4 = 4D/a But y4 = 3.6 mm, ∴
-7
the distance from the central = y4 a/4D = 6.3x10 m
th
axis [n = 0] to the 4 bright
fringe [n = 4]: i.e. 4 spaces  If the statement means the spacing [y3]
between 4 bright fringes: i.e. 3 spaces
 Either: y3 = 3.6 mm, ∴ y = y3/3 =3.6 mm /3
-3
= 1.2 mm or 1.2 x10 m.
-7
∴ = ya/D = 8.4 x10 m
 Or: y3 = 3.6 mm, ∴ = y3 a/3D = 8.4
-7
x10 m

 If the statement means the distance from the
th
central axis to the 4 dark fringe

[n = 0 to 4]: i.e. 3 spaces

 Either: y3.5 = 3.6 mm, y = y3.5/3.5 =3.6

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