Oscillations, Waves (Primers) and Modern

Question 1

Simple Harmonic Motion (SHM)

Answer 1

Simple harmonic motion is defined as a to-and-fro periodic motion of a body about an equilibrium point where its magnitude of acceleration is directly proportional to its magnitude of displacement, and acceleration is always directed towards the equilibrium position (i.e. acceleration and displacement are in opposite directions).

Question 2

oscillation: amplitude, period, frequency

Answer 2

maximum displacement of the oscillating body; time taken for one complete oscillation; the number of complete oscillations per unit time

Question 3

angular frequency

Answer 3

angular displacement per unit time

Question 4

phase, phase difference

Answer 4

the fraction of a period a point completes after last passing through the reference position; the fraction of a cycle by which one oscillation is ahead or behind another.

Question 5

Forced oscillation

Answer 5

A forced oscillation is the oscillation of a driven system which is maintained by an external periodic driver which applies a periodic driving force on the driven system continuously.

Energy is continuously supplied by the external periodic driver to the driven system) and the driven system oscillates at the driving frequency (of the external periodic driver)

Question 6

Resonance

Answer 6

Resonance is a phenomenon exhibited by a driven system acted upon by an external periodic driver continuously, occurs when driving frequency approaches/is equal to the natural frequency of the driven system

there is maximum energy transfer from the external periodic driver to the driven system, driven system has the maximum amplitude. Driven system and external periodic driver are 90 degrees out of phase.

Question 7

waves: amplitude, period, frequency

Answer 7

the magnitude of the maximum displacement of a wave disturbance from its equilibrium position; time taken for a particle in the wave to complete one cycle of an oscillation; the number of waves passing through a fixed point in a transmitting medium per unit time.

Question 8

wavelength

Answer 8

Wavelength is the distance between any two adjacent points on the wave having the same phase at a given instant.

Question 9

wavefront

Answer 9

Wavefront is a line or surface joining points of a wave that are in phase.

Question 10

waves: phase difference

Answer 10

Phase difference is a measure, in angular form, of the fraction of a cycle by which two particles in a wave or two waves are out of step with each other.

Question 11

Tranverse/Longitudinal

Answer 11

Transverse waves are waves in which the wave vibration is perpendicular/parallel to the direction of wave propagation/transfer of energy.

Question 12

Polarisation

Answer 12

Polarisation means to restrict the vibrations of a transverse wave to one plane (axis).

Question 13

Diffraction

Answer 13

Diffraction is the spreading of a wave into its geometrical shadow when it is incident on an edge of an obstacle or an aperture/opening.

Question 14

Principle of Superposition

Answer 14

The principle of superposition states that the net displacement at a given place and time caused by two or more waves which traverse the same space and meet is the vector sum of the displacement which would have been produced by the individual waves separately at that position and instant of time.

Question 15

Rayleigh criterion

Answer 15

The Rayleigh criterion states that the two images are just resolved when the central maximum of one diffraction pattern falls on the first minimum of the diffraction pattern.

Question 16

Stationary wave

Answer 16

A stationary wave is formed when two progressive waves of equal amplitude, equal frequency and same speed, meet when they travel in opposite directions.

Question 17

photon

Answer 17

A photon is a quantum (i.e. a discrete amount) of energy of electromagnetic radiation and its energy E, is given by E = hf where h is the Planck’s constant and f the frequency of the radiation.

Question 18

Work function

Answer 18

The work function of a metal is the minimum energy to release an electron (the most energetic electron) from the surface of the emitter metal.

Question 19

Threshold frequency

Answer 19

Threshold frequency is the minimum frequency of incident electromagnetic radiation to release an electron from the surface of the metal.

Question 20

Ionisation energy

Answer 20

Ionisation energy is required to completely remove an electron initially in the ground state from an atom.

Question 21

Excitation energy

Answer 21

Excitation energy is the energy required to raise an atom from its ground state to an excited state.

Question 22

Ground state

Answer 22

Lowest energy level in an atom

Question 23

Isotopes

Answer 23

Isotopes are atoms of the same element with the same number of protons but with different number of neutrons in their nucleus.

Question 24

Mass defect

Answer 24

Mass defect is the difference between the sum of the mass individual nucleons that makes up the nucleus and mass of the nucleus itself.

Question 25

Binding Energy

Answer 25

Binding energy is the **minimum** external energy required to **completely separate** all the neutrons and protons of a nucleus **to infinity**.

Question 26

Nuclear Fission

Answer 26

Nuclear fission is the **disintegration** of a *massive nucleus* into ***smaller** fragments of **comparable** masses* with the **release of a large amount of energy** as *the total mass of the daughter products is lower than the parent nuclei.*

Question 27

Nuclear Fusion

Answer 27

Nuclear fusion is the **combining or fusing** of two *light* nuclei to produce a *heavier* nucleus with the **release of a large amount of energy** as *the nucleus formed has a lower total mass than that of the parent nuclei*.

Question 28

Radioactive decay

Answer 28

Radioactive decay is a **naturally occurring**, **random** and **spontaenous** process in which the nucleus of an **unstable** atom will **spontaneously change** into a *different nuclear configuration* by the emission of combinations of *alpha particles*, *beta particles* and* gamma radiation*.

Question 29

Spontaneous

Answer 29

A spontaneous process is **not affected** by the **presence of other nuclei**. Also, the decay of a nucleus cannot be affected by chemical reactions or **physical conditions** such as temperature and pressure.

Question 30

random decay

Answer 30

it is impossible to predict when a particular nucleus in a sample is going to decay

Question 31

half-life

Answer 31

The half-life of a radioactive nuclide is the **mean** time taken for a quantity x to **reduce to half** its initial value where x represents either the *number*, *activity* or *count rate* of radioactive nuclei.

Question 32

Decay constant

Answer 32

The decay constant represents the **probability per unit time** that *a nucleus* will undergo decay.

Question 33

Activity

Answer 33

The activity of a radioactive source is the **number of decays** (or disintegrations) **per unit time**.