Workbook 2

Question 1

Define the Moment of a Force

Answer 1

The moment of a force about a point is defined as the turning effect that is caused by a force which is exerted at a perpendicular distance away from a fixed point.

Question 2

State the conditions for equilibrium

Answer 2

1. The resultant force on the object must equal zero.
2. The sum of the clockwise moment is equal to the sum of the anticlockwise moment about a pivoting point. (The Principle of Moments)

Question 3

Define a couple

Answer 3

A couple is defined as being a pair of forces, equal in magnitude, oppositely directed and whose line of action is on either side of the pivot.

Question 4

What is the centre of gravity of an object?

Answer 4

The centre of gravity of an object is the point where all the weight of the object seems to act.

Question 5

Define the Moment of Inertia of a rigid body

Answer 5

The moment of inertia of rigid body about a particular axis of rotation is defined as being a measure of the object’s resistance to a change in rotational motion about that axis.

Question 6

What is the moment of inertia dependant on?

Answer 6

It is dependant on the amount of mass of the object and its distribution.

Question 7

State the Principle of Conservation of Angular Momentum

Answer 7

The Principle of conservation of angular momentum states that the total angular momentum in a system of rotating bodies is conserved provided there is no resultant external torque acting on the system.

Question 8

Define Density

Answer 8

The density of a substance is defined as the mass per unit volume of a substance.

Question 9

Define Pressure

Answer 9

Pressure can be defined as being the force per unit area.

Question 10

What does pressure exerted by a liquid on an object depend on?

Answer 10

1. Density of the liquid
2. The acceleration due to gravity
3. The depth the object is within the liquid

Question 11

State Pascal’s Principle

Answer 11

Pascal’s Principle states that a change in the pressure applied to a fluid is transmitted undiminished to every point of the fluid and to the walls of the container.

Question 12

Springs in series vs springs in parallel

Answer 12

Springs in series each extend by extension ‘x’, therefore the total extension is 2x. This makes the system less stiff and lowers the effective spring constant.
Springs in parallel each extend by ‘x/2’, therefore the total extension is x. This makes the system more stiff and increases the effective spring constant.

Question 13

Define the Young’s Modulus of a Material

Answer 13

The Young’s Modulus gives a measure of the stiffness of a particular material.

Question 14

Define Tensile strain

Answer 14

Tensile stain is a measure of the deformation of a body due to an external tension.

Question 15

Define Tensile Stress

Answer 15

Tensile Stress is a measure of the internal forces a linear body experiences per unit cross-sectional area.

Question 16

Define Stiff, Strong, Brittle, Ductile.

Answer 16

1. Stiffness is a measure of how difficult it is to deform a material whilst in its elastic stage. A stiff material gives a small extension for a fairly large amount of force.
2. Strength of a material is dependable on how difficult it is to permanently deform or break the material. Such a material may not be stiff, but if it keeps giving extension for larger amounts of forces without breaking, then it will be strong.
3. Brittle materials are those that break shortly after the proportional limit.
4. Ductile materials are those that tend to keep on giving an extension for a long period of time beyond the proportional limit.

Question 17

Define limit of proportionality, elastic limit, yield point and ultimate tensile stress.

Answer 17

1.Up to that point, the values of stress and strain vary proportionally.
2. Exceeding the elastic limit will result in a permanent deformation and will not regain its original dimensions when no force is applied.
3. This marks the beginning of the plastic stage. From this point onwards a material gives larger extensions for a minimal increase in force.
4. This is the maximum stress that a material can withstand. Once this exceeded, the material will eventually break.

Question 18

What happens to rubber when loading and unloading?

Answer 18

When loading rubber, more energy is given to the material then what it gives back. The loop formed between the two graph is know as the hysterisis loop. This represents the amount of energy that the material keeps to itself which is generally dissipated as heat.

Question 19

Define wavelength

Answer 19

Wavelength is the distance between two successive crests or troughs.

Question 20

Define frequency

Answer 20

Frequency is the number of wavelength that pass a given plane in space per second.

Question 21

What does variation in colour depend on?

Answer 21

Frequency

Question 22

Define a wave

Answer 22

A wave if a mode of transfer of energy.

Question 23

Rays of light are predominantly straight unless acted upon by three factors which are…

Answer 23

1. reflection
2. refraction
3. by a gravitational pull

Question 24

State the Laws of Reflection

Answer 24

The laws of reflection state that the angle of incidence is equal to the angle of reflection and the incident ray, the normal and the reflected ray all lie in the same plane.

Question 25

Define refraction

Answer 25

Refraction is the bending of light that is caused by the slowing down or speeding up of light as it passes through media of different densities. A denser transparent medium will slow light more than a less dense transparent medium.

Question 26

State the Laws of Refraction.

Answer 26

The laws of refraction state that the incident rays, the normal and the refracted ray at the point of incidence all lie on the same plane.
Snell’s Law states that the ratio of the sine of the angle of incidence and the sine of the angle of refraction is a constant.

Question 27

What is the relative refractive index?

Answer 27

The relative refractive index is the factor by which light changes velocity with respect to any medium other than air/vacuum.

Question 28

What is the critical angle?

Answer 28

If light from a denser transparent medium is incident at the surface of a less dense medium at an angle equal to the critical angle, it will be refracted at 90 degrees to the normal.

Question 29

When does total internal reflection occur?

Answer 29

Total internal reflection occurs when a ray of light passing from a denser medium to a less dense medium tries to enter at an angle of incidence greater than the critical angle. The beam of light then gets reflected back into the denser medium and the laws of reflection apply.

Question 30

Name one limitation of optical fibres.

Answer 30

The light transmitted through it must have a very narrow spread of wavelength. This is because upon entering, the light refracts and since different wavelengths refract at different speeds, having a wide range of wavelength means that parts of the beam will arrive before the others, thus destroying the signal (distortion).

Question 31

Why does dispersion of light occur?

Answer 31

Dispersion of light occurs when white light passes through a prism. This is because white light is made up of different wavelengths which are all slowed down to different speeds and thus refracted at different angles. This separates the different colours.

Question 32

How are mirages formed?

Answer 32

Mirages are formed due to different densities of air. The closer to the ground, the colder the air and the denser the air. Light is refracted towards normal till angle is greater than critical angle and total internal reflection occurs, therefore, the sky blue seems to be seen on the ground floor.

Question 33

Distinguish between the frequency and periodic time.

Answer 33

Frequency is the number of oscillations per second and the periodic time is the time taken for one oscillation.

Question 34

What defines a body performing SHM?

Answer 34

A body performing SHM is one which has its acceleration directly proportional to its displacement and always directed towards its equilibrium position.

Question 35

What is damping?

Answer 35

Damping takes place when the oscillating body does not have constant amplitude, but a diminishing one. This occurs when energy is being taken away from the system with every oscillation.

Question 36

What is resonance?

Answer 36

Resonance is characterized by an appreciable increase in amplitude of oscillation. This occurs when a system is forced to oscillate (driving force) with a frequency comparable to its natural frequency.

Question 37

What are progressive waves?

Answer 37

Progressive waves are waves which transfer energy from one point to another.

Question 38

What is a mechanical wave?

Answer 38

A mechanical wave is one whose particles of a medium oscillate in simple harmonic motion.

Question 39

Distinguish between transverse and longitudinal waves.

Answer 39

Transverse waves are waves whose particles oscillate perpendicular to the direction of propagation whilst longitudinal waves are waves whose particles oscillate parallel to the direction of propagation.

Question 40

What is plane polarisation?

Answer 40

Plane polarisation is a method of distinguishing transverse and longitudinal waves. When a plane polariser is used, the vibrations in a particular plane, which is the same orientation as the slit will be let through, however, the vibrations in the other planes will be stopped. This results in a wave with vibrations in one plane.

Question 41

Define phase difference.

Answer 41

Phase difference is the angle that describes the offset between the oscillation of two or more particles in a medium, i.e. how much out of sync they are.

Question 42

What is the speed of sound dependent on?

Answer 42

The density, temperature and elasticity of the media the sound is travelling through.

Question 43

What is the Principle of Superposition?

Answer 43

The Principle of Superposition states that when two or more waves simultaneously pass through a point, the disturbance at the point is given by the sum of the disturbances each wave would produce in absence of the other waves.

Question 44

Distinguish between Constructive and Destructive interference.

Answer 44

Constructive interference occurs when a crest meets a crest or a trough meets a trough, whilst, destructive interference occurs when a crest meets a trough. Constructive interference is when the resultant wave pulse at the point of overlap has a higher amplitude than either wave pulse.
Destructive interference is when the resultant wave point at the point of overland has a smaller amplitude than one of the wave pulses.

Question 45

Requirements for interference:

Answer 45

Waves must have same frequency and wavelength.
In phase- constructive interference
out of phase- destructive interference

Question 46

How are standing waves formed?

Answer 46

When two waves are moving in the same space but opposing directions, they cross each others path and have the same frequency and wavelength.

Question 47

Why do stationary waves appear stationary?

Answer 47

There is no net energy transfer.

Question 48

List the differences between progressive waves and standing waves.

Answer 48

1. In progressive waves, the wave profile is seen to move, indicating that energy is being transferred whilst in stationary waves the wave profile is stationary, indicating that no net energy is transferred.
2. In progressive waves, all points oscillate with the same amplitude. In stationary waves, all points oscillate with different amplitudes, varying from zero at nodes to maximum at antinodes.
3. In progressive waves, points within a wavelength are out of phase. Points in phase are exactly 1 wavelength apart. In stationary waves, points with a loop are in phase but are out of phase with points in the adjacent loop.

Question 49

What is diffraction?

Answer 49

Diffraction is the term used to describe the way waves behave when they encounter an obstacle- the shape of the wavelength changes.

Question 50

How does diffraction depend on the width of gap and wavelength of the wave?

Answer 50

The amount of diffraction increases when the width of the gap is comparable to the wavelength.

Question 51

Define wavefront

Answer 51

Wavefront is a surface over which all points have the same phase.

Question 52

State Huygens’ Principle

Answer 52

Huygens’ Principle states that every point on a wavefront may be considered to be a source of secondary spherical wavelets that spread out in the forwards direction. The new wavefront is the tangential surface to all of the secondary points.

Question 53

What is Rayleigh’s Criterion?

Answer 53

Rayleigh’s Criterion states that two point sources are considered just resolved when the central maximum of one of the diffraction patterns coincides with the first minimum of the second.

Question 54

How does path difference from two slits result in constructive interference and destructive interference?

Answer 54

A path difference of a whole number of wavelengths will always result in constructive interference, a bright fringe, whilst a path difference of n +1/2 wavelength will always result in destructive interference, a dark fringe.