AL Test Solution Solids
Section A : BCEAE EBCBA
Section B
1. a) To remain horizontal
es = eb = e
Fb 
Eb A
e
L
and
[10]
[1]
Fs 
Es A
e
L
[1]
Take moment about the point placing the weight,
Fb d b  Fs d s 
d b Fs E s 2



d s Fb Eb 1
[1]
d b  d s = 900 mm
so d b = 600 mm, d s = 300 mm
and
[1]
So the weight should be attached to a point 300 mm from D.
b) Fs  Fb  3000
( Eb  E s )
[1]
Ae
= 3000 e = 3.18 mm
L
c) Brass wire :
[1]
Energy stored per unit volume =
=
=
Steel wire :
Energy stored per unit volume =
=
=
1
Eb  b2
2
1
0.00318 2
(1  1011 )(
)
2
1
[1]
5.07  10 5 J m-3
1
E s  s2
2
1
0.00318 2
(2  1011 )(
)
2
1
[1]
1.01  10 6 J m-3
[1]
9
2. a)
r / 10-10 m
Resultant force F / 10-10 N
2.0
4.0
2.2
2.0
2.4
0
8.4 10.0
-0.4 -0.2
[1]
axis [1],
points [1]
smooth curve [1]
[3]
b) The graph is a straight line near the equilibrium separation. This can be concluded that the
intermolecular force is directly proportional the change in the intermolecular separation. This is similar
to the behaviour of a spring which produce a force directly proportional to its extension. So I agree with
the suggestion.
[3]
c) the equilibrium separation is 2.4 × 10-10 m.
d) i)
Breaking stress =
ii) k
=
=
=
2.8  10 10
2.6
-1.0
2.8
-2.0
3.2
-2.4
4.0
-2.8
4.8
-2.4
5.6
-2.0
7.2
-0.8
[1]
(2.4  10 10 ) 2
[1]
= 4.86 × 109 N m-2
|slope at ro|
[1]
[1  (1)]  10 10
(2.3  2.5)  10 10
10
[1]
E
=
k
ro
10
=
2.4  10 10
[1]
=
4.17 × 1010 N m-2
[1]
13
3. a) i)
Force must be applied to extend a solid, thus attractive force exists between atoms to hold them
together. A solid is hard to compress, this shows that repulsive force exists when atoms are pushed
closer together. When a moderate applied force on a solid is removed, it restores to its original
shape which reflects the restoring behaviour of springs.
[2.5]
ii) The curve of potential energy, U, against interatomic separation, r, is as follows:
[1]
At a certain temperature, the atoms with total energy E1 vibrate between A and B with mean
separation r1. At a higher temperature, the KE and thus the TE of the atoms increases. As the
vibration is asymmetrical with displacement greater on the extension side, so at higher energy E2,
atoms vibrate between C and D with increased mean separation r2. So the solid expands.
[2.5]
b) Glass is strong as a large breaking stress is required to break it. Glass is stiff as a large stress only
gives a small strain. So the graph has a great slope. Glass is brittle as it shows no plastic
deformation.
[2]
[1]
9
4. Ionic Bond :
[0.5]
It is formed between elements at opposite sides of periodic table, e.g. Na (group 1) and Cl (group
7). Na atom has loosely held outer electron which is accepted by a Cl atom. Ions are formed as
shown in the diagram and are bound by strong electrostatic attractions.
[1.5]
Covalent Bond :
[0.5]
Sharing of electrons takes place between two or more atoms, e.g. each C atom has four outer
electrons and these can be shard with four other atoms by overlapping electron clouds.
[1.5]
Metallic bond
In a metal, outer electrons are loosely held by atoms and drift around randomly as free electrons.
All the atoms share these free electrons and the strong attraction between the positive ions and the
electrons forms a metallic bond.
[2]
6