Quantum

Question 1

Photon

Answer 1

discrete packet of energy of electromagnetic radiation. The energy of one photon is directly proportional to the frequency of electromagnetic radiation.

Question 2

Photoelectric effect

Answer 2

emission of electrons when electromagnetic radiation of high-enough frequency is incident on a cold metal surface

Question 3

Work function

Answer 3

The work function of a metal is the minimum energy needed to remove the least tightly bound electron from the metal’s surface.

Question 4

Threshold frequency

Answer 4

The threshold frequency is the minimum frequency of electromagnetic radiation for electrons to be removed from the metal’s surface

Question 5

Stopping Potential

Answer 5

The stopping potential is the minimum potential difference between the emitting metal and the collector that prevents the most energetic photoelectrons from reaching the collector plate, thus resulting in 0 photoelectric current.

Question 6

Evidence/observations from photoelectric emission that provide evidence for particulate nature of electromagnetic radiation

Answer 6

1. Emission of electrons only when electromagnetic radiation is above a minimum frequency regardless of intensity
2. Maximum kinetic energy of electrons depends on frequency of electromagnetic radiation
   Maximum kinetic energy of electrons is independent of intensity
3. Instantaneous emission of electrons when electromagnetic radiation is above a certain frequency

Question 7

Absorption Spectra

Answer 7

An absorption spectra is a continuous spectrum crossed by dark lines.

Question 8

Emission Spectra

Answer 8

An emission spectra is discrete bright lines of different colours on a dark background.

Question 9

De Broglie Wavelength

Answer 9

The De Broglie Wavelength is the wavelength of the matter wave that is associated with a moving particle.

Question 10

Excitement of atoms

Answer 10

When atoms are excited, an orbiting electron takes in energy to move to a higher energy level.

Question 11

Heisenberg’s Uncertainty Principle

Answer 11

If a measurement of position is made with precision Δx and a simultaneous measurement of momentum is made with precision Δp the product of those two uncertainties can never be smaller than the Planck constant. (ΔxΔp≥h)

Question 12

Spectra as proof of discrete energy levels in the atom

Answer 12

1. Each coloured/dark line corresponds to one wavelength or frequency,
2. representing photons of a specific energy given by E=hf
3. that is emitted/absorbed when orbital electrons undergo energy changes
4. when de-exciting/exciting between discrete energy levels in the atom.
   (Absorbed photons are then re-emitted in all directions shortly when the unstable, excited atom de-excites.)

Question 13

Broad Continuous Background in X-ray spectrum (Braking Radiation)

Answer 13

X-ray photons are produced when the electrons/charged particles are stopped or decelerated suddenly. When electrons/charged particles strike the target metal, they experience a range of decelerations, so photons possess a continuous distribution of energies, and hence have a continuous distribution of wavelengths.

Question 14

Minimum wavelength appears as a sharp cut-off

Answer 14

The minimum wavelength corresponds to the most energetic photons, which are produced when all kinetic energy of one electron/charged particle is converted into one X-ray photon.

Question 15

Characteristic peaks in X-ray Spectrum

Answer 15

When bombarding electrons collide with orbiting inner shell electrons of the metal atoms with sufficient energy, the inner shell electron is ejected. Outer shell electrons will transit to the lower energy level, releasing an X-ray photon of photon energy exactly equal to the difference between the two energy levels.

Question 16

N1L

Answer 16

An object will continue to be in a state of rest or move with constant velocity, unless acted upon by a net external force.

Question 17

N2L

Answer 17

The rate of change of momentum of a body is directly proportional to the resultant force acting on it, and takes place in the direction of the resultant force.

Question 18

N3L

Answer 18

When object A exerts a force on object B, object B will exert an oppositely directed force of the same type of equal magnitude on object A.

Question 19

Impulse

Answer 19

The impulse of a force is the product of the average force and the time interval during which the force acts. or
The impulse of a force is the integral of a force over the time interval during which the force acts.

Question 20

PCM

Answer 20

The total linear momentum of an isolated system of interacting bodies before and after collision remains constant provided that no net external force acts on the system.

Question 21

Diffraction

Answer 21

Diffraction is the spreading of waves towards the geometric shadow after passing through an aperture.

Question 22

Interference

Answer 22

Interference is the phenomenon observed when waves from two (or more) coherent sources overlap and, in accordance to the Principle of Superposition, produces a pattern of maximas and minimas.

Question 23

Coherent

Answer 23

Sources are coherent if they produce waves that have a constant phase difference.

Question 24

Principle of Superposition

Answer 24

The Principle of Superposition states that when two or more waves of the same type meet, the resultant displacement at any point is the vector sum of the individual displacements that each wave would cause at that point.

Question 25

Rayleigh Criterion

Answer 25

The limit for which the two objects can be just distinguishable occurs when the first minima of the diffraction pattern of one source coincides with the central maxima of the diffraction pattern of the other source.

Question 26

Formation of Interference pattern

Answer 26

For steady and observable interference patterns, the following conditions must be met: 1. The waves must overlap. (For superposition to occur) 2. The waves from the sources must have constant phase difference (of the same type, have same wavelength and frequency). (For interference pattern to be formed) 3. The waves must have approximately the same amplitude. (For good contrast between maximas and minimas) 4. For transverse waves, they must either be unpolarised, or polarised in the same plane. (For good contrast between maximas and minimas) 5. Same nature of wave (1 and 2 make the pattern observable, point 3 and 4 give it good contrast)

Question 27

Simple Harmonic Motion

Answer 27

Simple Harmonic Motion is a type of oscillatory motion where: 1) the magnitude of the acceleration is always directly proportional to the displacement from the reference point, and 2) the acceleration is directed opposite to its displacement.

Question 28

Critical Damping

Answer 28

The point at which no complete oscillation takes place, and the time taken for the oscillating body to come to rest is the shortest.

Question 29

Resonance

Answer 29

The phenomenon in which there is maximum transfer of energy from the driver to the oscillator when the driving frequency matches the natural frequency of the undamped oscillator. The oscillations will achieve maximum amplitude.

Question 30

Equilibrium Position

Answer 30

Equilibrium Position is the natural position of the mass where no net force acts on the oscillating mass.

Question 31

Free oscillations

Answer 31

constant vibration amplitude of oscillating body without energy loss (due to lack of resistance forces or external applied forces)

Question 32

Angular Frequency (⍵)

Answer 32

Angular frequency is the rate of change of phase of the oscillating mass.

Question 33

Phase difference

Answer 33

Phase difference is a measure of how much an oscillation is out of step with itself at 2 different instances in time, or how much 2 oscillations are out of step with each other at the same instant in time.

Question 34

Phase

Answer 34

Phase is an angular measure of the fraction of a cycle that has been completed by the oscillating mass.

Question 35

Frequency

Answer 35

Frequency is the number of complete to-and-fro oscillations per unit time made by the oscillating mass.

Question 36

Displacement

Answer 36

Displacement is the position vector of the oscillating mass measured from its equilibrium position at a particular instant.

Question 37

Amplitude

Answer 37

Amplitude is the maximum displacement of the oscillating mass from the equilibrium position in either direction.

Question 38

Period

Answer 38

Period is the time taken for one complete oscillation of the oscillating mass.

Question 39

Random error

Answer 39

Measured readings are scattered about the mean value with no fixed pattern.

Question 40

Systematic error

Answer 40

Measurements that are consistently higher or lower than the actual value.

Question 41

Accuracy

Answer 41

The degree to which a reading on an instrument approaches the true value of the quantity being measured.

Question 42

Precision

Answer 42

How close the experimental values are to each other. OR The smallest interval to which an instrument can measure.

Question 43

Displacement, Velocity, Acceleration

Answer 43

Displacement Shortest distance, in a specific direction, from a reference point. Velocity Rate of change of displacement. Acceleration Rate of change of velocity.

Question 44

Elastic, inelastic, p. elastic collision

Answer 44

Elastic collision A perfectly elastic collision is one in which the total kinetic energies of the colliding bodies are conserved(remains constant before and after the collision). Inelastic collision An inelastic collision is one in which the sum of kinetic energies of the colliding bodies are not conserved. Total Kinetic energy after the collision is lesser than before it. Perfectly inelastic collision A perfectly inelastic collision is one in which the colliding bodies stick together and move off with the same velocity.

Question 45

Hooke’s Law

Answer 45

The change in length, x, of a material, is directly proportional to the force applied to it, F, provided the limit of proportionality is not exceeded.

Question 46

Archimedes’ Principle

Answer 46

When a body is wholly or partially immersed in a fluid, it is buoyed by an upthrust equal in magnitude and opposite in direction to the weight of fluid displaced by the body.

Question 47

Centre of gravity

Answer 47

The point where all the weight seems to act.

Question 48

Couple

Answer 48

A couple is a pair of forces acting on the same body, which are of equal magnitude and opposite in direction and whose lines of action do not coincide.

Question 49

Upthrust

Answer 49

Upthrust is the upward force exerted by a fluid on an object submerged fully or partially in the fluid due to the difference in pressure exerted by the fluid on the upper and lower surfaces of the object. It acts through the centre of mass of the displaced fluid and is equal in magnitude and opposite in direction to the weight of fluid displaced by the body.

Question 50

Conditions for Equilibrium

Answer 50

Translational Equilibrium: The vector sum of forces acting on the body must be 0 along all directions. Rotational Equilibrium: The net torque acting on the body must be 0 about all axes.

Question 51

Principle of Moments

Answer 51

For an object in rotational equilibrium, the sum of clockwise moments acting on the object about any point must be equal to the sum of anticlockwise moments acting on the object about the same point.

Question 52

Work

Answer 52

The work done on a body by a force is the product of the force and the displacement of the body in the direction of the force.

Question 53

Law of conservation of energy

Answer 53

Energy can be converted from one form to another but cannot be created or destroyed. The total energy of an isolated system is always constant.

Question 54

Power

Answer 54

Rate of work done.

Question 55

Radian, Ang disp, ang vel

Answer 55

Radian The radian is the angle subtended at the centre of a circle by an arc whose length is equal to the radius of the circle. Angular displacement The angular displacement is the angle swept out by the radius, in a specific direction from the original position. Angular velocity Angular velocity is the rate of change of angular displacement.

Question 56

How uniform circular motion arises

Answer 56

Force* always perpendicular to motion of the object no displacement in the direction of the force and hence no work done by force and the KE of the object is constant thus, the force being constant in magnitude merely provides centripetal force required for the object to undergo uniform circular motion.

Question 57

Why is there no work done during circular motion

Answer 57

Force* that provides centripetal force for the object to undergo uniform circular motion is always perpendicular to the motion of the object. As such, there is no displacement in the direction of the force and hence, there is no work done.

Question 58

Gravitational Field

Answer 58

A gravitational field is a region of space in which a mass experiences a gravitational force.

Question 59

Gravitational Potential

Answer 59

Work done per unit mass (by an external force) in bringing a small test mass from infinity to that point in the field.

Question 60

Gravitational Potential Energy at a point

Answer 60

The work done by an external force in bringing the mass from infinity to that point in the field.

Question 61

Gravitational Field Strength

Answer 61

The gravitational force per unit mass experienced by a small test mass at that point in the field. (Small and test are important because they highlight the idea that the mass should not distort the pre-existing gravitational field. Similar idea for E-field: small test charge.)

Question 62

Newton’s Law of Gravitation

Answer 62

The gravitational force of attraction between any two masses is directly proportional to the product of their masses and inversely proportional to the square of the distance between them [magnitude] and acts along the line joining the two point masses [direction]

Question 63

Geostationary

Answer 63

A geostationary satellite is one which always remains at a fixed point above the Earth’s surface. Properties: Orbital axis coincides with that of earth’s rotation. Same orbital period as earth (24 hours) Orbits around the equator in the west to east direction.

Question 64

Relationship between Gravitational potential and gravitational field strength.

Answer 64

Gravitational field strength at a point is numerically equal to the gravitational potential gradient at that point and directed towards lower potential.

Question 65

The acceleration of free fall at the Equator is not equal to the acceleration of free fall at the poles. Explain why they are different.

Answer 65

At the equator, part of the acceleration of free fall provides centripetal force for circular motion. Since the radius of circular motion at the equator is larger, an object experiences greater centripetal force, so the acceleration of free fall is lower than at the poles.

Question 66

By reference to lines of gravitational force near to the surface of the Earth, explain why the gravitational field strength g close to the Earth’s surface is approximately constant.

Answer 66

At the surface, lines of gravitational force are radial Earth has a large radius, so lines are equally spaced and approximately parallel near the surface Parallel lines means there is constant field strength

Question 67

Why gravitational potential is a negative value for an isolated mass.

Answer 67

Gravitational potential at infinity is defined as zero. Gravitational forces are attractive, so work done by an external force is opposite to displacement. (Work is done by the external force against the field) Work done per unit mass by the external agent is negative/Loss in gravitational potential energy when moving from infinity to the point. (Since the mass begins at 0 gravitational potential energy, a loss in gravitational potential energy results in a negative value for gravitational potential.)

Question 68

The acceleration of free fall at the Equator is not equal to the acceleration of free fall at the poles. Explain why they are different.

Answer 68

At the equator, part of the acceleration of free fall provides centripetal force for circular motion. Since the radius of circular motion at the equator is larger, an object experiences greater centripetal force, so the acceleration of free fall is lower than at the poles.

Question 69

Explain, in terms of energy, the impact of atmospheric drag on the subsequent trajectory of geostationary satellites.

Answer 69

Work is done against drag, total energy (-GMm2r) decreases. Gravitational potential energy (-GMmr) decreases, satellite lowers in height. Kinetic energy (GMm2r) increases, satellite’s linear speed increases. Satellite spirals to Earth with increasing speed.

Question 70

Explain why the centripetal force acting on 2 stars has the same magnitude.

Answer 70

Gravitational force provides centripetal force for their circular motion By Newton’s 3rd Law, both stars experience the same magnitude of gravitational force

Question 71

It is then required to reposition the satellite at an orbit closer to the Sun than that in (d). State and explain whether the work done on the satellite is positive, negative, or zero to change the position of the satellite to a lower orbit. Effect of orbital radius on total energy

Answer 71

Changing satellite to a lower orbit, the gain in KE is less than the loss in PE OR Total energy decreases. Hence Negative work is done. -GMmr+GMm2r=-GMm2r(PE+KE=Total Energy, r decreases, total energy decreases.)

Question 72

Thermal equilibrium

Answer 72

When two bodies are in thermal equilibrium, there is no net flow of heat between them when they are in thermal contact.

Question 73

Avogadro’s Number

Answer 73

Avogadro’s number is the number of atoms in 12g of carbon-12.

Question 74

Absolute zero

Answer 74

Absolute zero is defined as the zero point on the absolute temperature scale.

Question 75

Ideal Gas

Answer 75

An ideal gas obeys the equation of state: PV=nRT, at all pressures P, at all volumes V, for all moles of the gas n, at all temperatures T, where R is the molar gas constant.

Question 76

Heat

Answer 76

Heat is thermal energy that flows from a region of higher temperature to a region of lower temperature.

Question 77

Thermometric property

Answer 77

A thermometric property of a substance is one which varies with temperature.