Solids and Fluid Dynamics

Physics · 11th Class (Intermediate Part 1) · BISE Lahore

70 questions

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Solids and Fluid Dynamics Test

10 questions · Solids and Fluid Dynamics × 10

Sample questions

Showing 20 of 70 questions from this chapter. The full bank is in the chapter test below.

1
A solid in which the atoms, molecules or ions are arranged in a regular pattern that is repeated consistently throughout the material is called
- A.an amorphous solid
- B.a crystalline solid (correct answer)
- C.a glassy solid
- D.a polymeric solid
Why: A crystalline solid has long-range order, so its particles occupy regular positions that repeat throughout the crystal. Amorphous (glassy) solids are disordered, and polymeric solids are only partially ordered.
2
The regular arrangement of the atoms, molecules or ions inside a crystalline solid is investigated using
- A.X-ray diffraction and transmission electron microscopy (correct answer)
- B.a screw gauge and a spirit level
- C.a venturi meter and a manometer
- D.a metre scale and a micrometer
Why: X-ray diffraction (XRD) and transmission electron microscopy (TEM) probe the internal periodic arrangement of a crystal. The other instruments measure length, level, pressure or flow rate and reveal nothing about atomic order.
3
Which statement describes an amorphous solid?
- A.It has a sharp and definite melting point.
- B.Its particles show regular long-range order.
- C.It softens gradually over a range of temperature instead of melting sharply. (correct answer)
- D.It cannot be heated above room temperature.
Why: Because an amorphous solid has a disordered structure, heating makes it soften gradually into a paste-like state, so it has no definite melting point. A sharp melting point is a characteristic of crystalline solids.
4
Which of the following is an amorphous (glassy) solid?
- A.Quartz
- B.Calcite
- C.Sugar
- D.Ordinary glass (correct answer)
Why: Ordinary glass has no regular arrangement of its molecules and is therefore classed as an amorphous, or glassy, solid. Quartz, calcite and sugar are crystalline solids with definite melting points.
5
The structure of a polymeric solid is best described as
- A.perfectly ordered, with long-range order in three dimensions
- B.completely disordered, like that of a liquid
- C.intermediate between order and disorder (correct answer)
- D.identical to that of an ionic crystal
Why: Polymers are classified as partially or poorly crystalline solids, so their long chain molecules are neither perfectly ordered nor completely random. This intermediate structure gives polymers their useful combination of flexibility and strength.
6
Which of the following is a polymeric solid?
- A.Copper
- B.Polythene (correct answer)
- C.Sodium chloride
- D.Diamond
Why: Polythene is made by polymerisation, in which simple molecules join into very long chain molecules, so it is a polymer. Copper and diamond are crystalline solids and sodium chloride is an ionic crystal.
7
Compared with metals, polymeric materials are characterised by
- A.low specific gravity together with a good strength-to-weight ratio (correct answer)
- B.very high specific gravity and poor strength
- C.an ordered crystal lattice and a sharp melting point
- D.very high thermal conductivity
Why: Polymers such as polythene, polystyrene and nylon are lighter than even the lightest metals, yet they are reasonably strong for their weight, which is why they are widely used as structural and packaging materials.
8
In a crystalline solid, the atoms
- A.stay completely at rest at their lattice points
- B.move freely from one end of the crystal to the other
- C.are held together only by gravitational attraction
- D.vibrate about fixed mean positions, with an amplitude that increases as the temperature rises (correct answer)
Why: The atoms are not static: each vibrates about its mean lattice position, and the amplitude grows with temperature until the structure breaks up and the solid melts. It is the average atomic positions that are perfectly ordered.
9
Deformation of a body means a change in its
- A.shape, length or volume (correct answer)
- B.mass only
- C.temperature only
- D.electrical resistance only
Why: Deformation is the change in shape, length or volume produced when a body is subjected to an external force, as when a rubber ball is squeezed or a wire is stretched.
10
The ability of a body to regain its original shape and size after the deforming force is removed is called
- A.plasticity
- B.viscosity
- C.elasticity (correct answer)
- D.ductility
Why: Elasticity is the property by which a body returns to its original state once the applied force is removed, provided the force was not too large. Plasticity, by contrast, is a permanent change of shape.
11
Stress is defined as the
- A.change in length per unit original length
- B.force applied per unit area (correct answer)
- C.product of the applied force and the extension
- D.force applied per unit volume
Why: Stress equals $F/A$ , the force applied per unit area, and it may change the length, the volume or the shape of a body. The change in length per unit original length is strain, which is a different quantity.
12
The SI unit of stress, the newton per square metre, is given the name
- A.newton (N)
- B.joule (J)
- C.pascal (Pa) (correct answer)
- D.watt (W)
Why: Stress is force per unit area, so its unit is $\mathrm{N\,m^{-2}}$ , which is named the pascal. The newton measures force, the joule energy and the watt power.
13
Because strain is the ratio of two lengths, it
- A.is dimensionless and has no units (correct answer)
- B.is measured in metres
- C.is measured in $\mathrm{m^{-1}}$
- D.is measured in pascal
Why: The units of the change in length and of the original length cancel in the ratio, so strain is a pure number having neither units nor dimensions. The pascal is the unit of stress, not of strain.
14
If the volume of a solid changes from $V$ to $V + \Delta V$ under a volume stress, the volumetric strain is
- A. $V\Delta V$
- B. $\frac{V}{\Delta V}$
- C. $\frac{\Delta V}{V}$ (correct answer)
- D. $\frac{\Delta V}{V^{2}}$
Why: Volumetric strain is the change in volume per unit original volume, that is $\frac{\Delta V}{V}$ . The inverted ratio $\frac{V}{\Delta V}$ is a common slip but is not the definition.
15
In a rigid block, two opposite faces are a perpendicular distance $y$ apart. If one face slides through a distance $\Delta x$ under a shear stress, the shear strain is
- A. $\frac{y}{\Delta x}$
- B. $\frac{\Delta x}{y^{2}}$
- C. $\Delta x \cdot y$
- D. $\frac{\Delta x}{y}$ (correct answer)
Why: Shear strain equals $\frac{\Delta x}{y}$ , which is also $\tan\theta$ , where $\theta$ is the small angle through which the block is distorted. For small angles, $\tan\theta = \theta$ in radians.
16
A vertical concrete pillar carrying a heavy load is squeezed along its length. The stress acting on the pillar is
- A.volume stress
- B.compressive stress (correct answer)
- C.tensile stress
- D.shear stress
Why: Forces that tend to shorten a body produce compressive stress, whereas tensile stress tends to lengthen it. Volume stress changes the volume of a body and shear stress changes its shape.
17
Young's modulus of a material is defined as the ratio of
- A.tensile strain to tensile stress
- B.the applied force to the extension produced
- C.stress to volume strain
- D.tensile stress to tensile strain (correct answer)
Why: Young's modulus is the tensile stress divided by the tensile strain, so it measures the stress needed to produce unit strain. Being a stress, it has the unit $\mathrm{N\,m^{-2}}$ , the same as that of stress.
18
For a wire stretched within its limit of proportionality, doubling the tensile strain will
- A.halve the tensile stress
- B.leave the tensile stress unchanged
- C.double the tensile stress (correct answer)
- D.halve Young's modulus of the material
Why: Within the limit of proportionality the stress is directly proportional to the strain, so doubling the strain doubles the stress. Young's modulus is a constant property of the material and does not change.
19
Which of the following materials is the most elastic?
- A.Steel (correct answer)
- B.Rubber
- C.Sponge
- D.Wood
Why: A material is more elastic when a larger stress is needed to produce the same strain, that is when its Young's modulus is larger. Steel ( $Y \approx 200 \times 10^{9}\ \mathrm{N\,m^{-2}}$ ) far exceeds rubber, sponge and wood, even though rubber stretches much more for a given force.
20
Two wires of the same length and cross-sectional area, one of aluminium ( $Y = 70 \times 10^{9}\ \mathrm{N\,m^{-2}}$ ) and one of steel ( $Y = 200 \times 10^{9}\ \mathrm{N\,m^{-2}}$ ), are stretched by equal forces. The extension of the aluminium wire is
- A.the same as that of the steel wire
- B.about 2.9 times the extension of the steel wire (correct answer)
- C.about 0.35 times the extension of the steel wire
- D.about 200 times the extension of the steel wire
Why: Since $\Delta L = \frac{FL}{AY}$ , for the same force, length and area the extension is inversely proportional to $Y$ , so the aluminium wire extends $\frac{200}{70} \approx 2.9$ times as much as the steel wire.

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