All Knowledge

Question 1

What is the definition of SHM

Answer 1

The restoring force acting on the object, when displaced from equilibrium position, is directed towards the centre and proportional to displacement from the equilibrium position

Question 2

For an object undergoing SHM, where are the velocity and acceleration respectively at there maximum

Answer 2

Velocity - centre point

Acceleration - extremities

Question 3

State the equation which defines SHM

Answer 3

acceleration = - (constant (angular velocity))*displacement

Question 4

Describe critical damping

Answer 4

Where the resistance to oscillation of the object is just sufficient to prevent any further oscillations without excessive time taken to return to equilibrium position

Question 5

Describe overdamping

Answer 5

Where the resistance to oscillation of the object is too great and so the object takes excessive time to return to equilibrium position

Question 6

Describe underdamping

Answer 6

Where the resistance to oscillation of the object is too little and so the object will oscillate multiple times before coming to rest at equilibrium position

Question 7

Describe the principle of superposition

Answer 7

The resultant disturbance from two or more waves can be represented by a single periodic wave which is given by the algebraic sum of all the individual waves.

Question 8

Describe how standing waves are formed

Answer 8

The interference of two waves of equal frequency travelling in opposite directions produces standing waves

Question 9

What is an anti-node

Answer 9

A point of maximum displacement

Question 10

What is a node

Answer 10

A point of no displacment

Question 11

What is the difference between a travelling wave and a stationary wave

Answer 11

A travelling wave radiates energy whereas a standing wave does not. Also, the crests of a standing wave are independent of time whereas the crests of a travelling wave change with time

Question 12

What condition makes two waves coherent

Answer 12

Constant phase difference

Question 13

What is the definition of optical path difference

Answer 13

optical path difference = refractive index * geometrical path difference

Question 14

What occurs when light, travelling through air, reflects off a medium of greater optical density

Answer 14

Pi rad phase change

Question 15

What occurs when light reflects off a medium of lower optical density

Answer 15

No phase change

Question 16

When does interference by division of amplitude occur

Answer 16

When a ray of light splits into two beams, by a material of greater optical density,with one ray being transmitted and other ray being reflected. When focused by an eye, both rays will combine and interfere.

Question 17

What is the condition for constructive interference in thin-film interference

Answer 17

2nt = (m+1/2)*wavelength

Question 18

What is the condition for destructive interference in thin-film interference

Answer 18

2nt = m*wavelength

Question 19

Why does a puddle with oil on it appear multi-coloured in the sunlight

Answer 19

The oil on the puddle acts as a thin-film hence it produces interference by division of amplitude. Sunlight is a continuous source and do is made up of all wavelengths of light which will all refract through oil differently produced coloured fringes. Also, differences in thickness of the oil produce a complex pattern of fringes.

Question 20

Why can an extended (non-coherent) source be used for interference by division of amplitude

Answer 20

Division of amplitude splits a single wave into two before recombining. The two beams that result from splitting a wave will always be coherent which means that we do not require a source of two coherent waves as only one wave is required.

Question 21

Why do glasses with a non-reflective coating appear purple

Answer 21

Complete cancellation of reflected light only occurs at a specific wavelength. For maximum coverage, this wavelength is often chosen in the middle of the visible spectrum. Hence, the wavelengths at the extremities of the spectrum, purple and blue, do not undergo destructive interference and instead combine producing a purple-reddish colour on the glasses.

Question 22

What kind of source must be used for interference by division of wavefront

Answer 22

A point source

Question 23

What is the difference between interference by division of amplitude and interference by division of wavefront?

Answer 23

Interference by division of amplitude involves splitting a single wave which is then combined producing interference effects whereas interference by division of wavefront involves the interference of two separate, coherent waves.

Question 24

Describe the Young’s Slit Experiment

Answer 24

A monochromatic source is incident on the double slit producing two secondary sources by division of wavefront. The slit separation must be in the order of the wavelength of light used and the distance to the screen must be much greater. The two secondary sources act as point sources and the overlap of the beams will produce an interference pattern.

Question 25

What is the difference between unpolarised and linearly polarised light?

Answer 25

The electric field vector of unpolarised light has equal probability of oscillating in every direction whereas polarised light only oscillates in a single plane.

Question 26

What type of waves can be polarised?

Answer 26

Transverse waves

Question 27

Describe Brewster’s Law of Polarisation

Answer 27

Brewster’s Law says that at a certain angle of incidence, the light reflected off a dielectric medium will be completely polarised. At all other angles, the light will be partially polarised.

Question 28

What is the angle between the reflected and transmitted ray at the Brewster Angle?

Answer 28

90 degrees

Question 29

Describe some applications of polarisation

Answer 29

Reduction of glare by polaroid sunglasses and camera lenses. When sunlight is reflected off the road or a body of water it will be partially polarised in the horizontal transmission axis therefore, a polariod in the vertical transmission axis will block glare from the road or water.