Chapters 4-7 R#1 Flashcards
1
Q
Chapter 4: Work, Energy, and Momentum
A
2
Q
What is the formula for work?
A
Work = Force × Distance
3
Q
What are the units of work?
A
Joules (J) or Newton-meters (Nm)
4
Q
What is the relationship between energy and work?
A
Energy is the capacity to do work; work and energy are equivalent.
5
Q
What is Gravitational Potential Energy (GPE), and what is its formula?
A
GPE is the energy an object has due to its height. Formula: GPE = mgh
6
Q
How can GPE be increased?
A
By increasing mass or height.
7
Q
What is Kinetic Energy (KE), and what is its formula?
A
- KE is the energy due to motion.
Formula: KE = ½ m v²
In many cases where an object comes to rest after a certain distance, it can be described as equal to work done against resistive forces
8
Q
What are some other forms of energy?
A
- Elastic potential energy (due to change in shape)
- Chemical energy (stored in chemical compounds)
- Thermal/Heat energy (lost due to friction)
- Nuclear energy (from radioactive elements)
- Solar energy (from the Sun’s light)
- Electric energy (due to charges)
9
Q
What is the law of conservation of energy?
A
Energy cannot be created nor destroyed, only transformed from one form to another
10
Q
How can we calculate velocity when only given height?
A
v = √(2gh)
11
Q
What happens to kinetic energy when an object hits the ground?
A
- If it stops immediately, all KE is lost as heat and sound.
- If it rebounds, some KE is lost as heat and sound.
If describing energy loss, say thermal energy & specify where it’s going
12
Q
How does air resistance affect energy?
A
Some energy is lost as heat and sound due to friction with air.
If describing energy loss, say thermal energy & specify where it’s going
13
Q
How is energy converted in a pendulum?
A
- At the highest points: All energy = GPE
- At the lowest points: Energy = KE + GPE
14
Q
How does friction affect a moving bicycle?
A
Some energy is lost as heat due to friction, reducing the KE at the lowest point.
15
Q
What is power, and what is its formula?
A
Power is the rate of doing work.
* Power = Work / Time
* Power = Energy / Time
* Power = Force × Velocity
16
Q
What are the units of power?
A
Watts (W) or Joules per second (J/s)
17
Q
What is efficiency, and how is it calculated?
A
Efficiency is the ratio of useful output energy to input energy.
* Efficiency = (Useful Output Work / Input Energy) × 100%
* Efficiency = (Useful Output Power / Input Power) × 100%
18
Q
How can we improve efficiency?
A
- Increase useful output energy
- Reduce wasted energy
- Use less input for the same result
19
Q
How do thermal power stations produce electricity?
A
They burn fuel or use nuclear reactions to boil water, producing high pressure steam that turns a turbine by transferring its kinetic energy to the turbines which are connected to and spin a generator.
20
Q
What resources, energy conversion process, and power‑station framework are used in fossil‑fuel stations?
A
- Resource: Coal, natural gas, oil
- Energy conversion: Chemical energy ⟶ Electrical energy
- Framework: Thermal power stations
21
Q
What are the advantages and disadvantages of fossil‑fuel power stations?
A
Advantages:
1. High useful output energy
2. Continuous generation
Disadvantages:
1. Non‑renewable
2. Increases pollution → global warming & acid rain
3. Produces noise
22
Q
What resources, energy conversion process, and framework are used in nuclear stations?
A
- Resource: Radioactive isotopes
- Energy conversion: Nuclear energy ⟶ Electrical energy
(By nuclear fission reaction) - Framework: Thermal power stations
23
Q
What are the advantages and disadvantages of nuclear power stations?
A
Advantages:
1. Very high useful energy output
2. Continuous, long‑term generation
Disadvantages:
1. Requires high safety measures
2. Non‑renewable
3. Produces hazardous nuclear waste
24
Q
What resources, energy conversion process, and framework are used in geothermal stations?
A
- Resource: Hot rocks deep underground
- Energy conversion: Thermal energy ⟶ Electrical energy
- Framework: Thermal power stations
25
What are the advantages and disadvantages of geothermal power stations?
**Advantages:**
1. Renewable
2. Clean (no direct emissions)
3. No fuel costs
**Disadvantages:**
1. Low output energy
2. Site‑limited
3. Expensive, difficult deep drilling
26
What resources, energy conversion process, and framework are used in hydroelectric stations?
* Resource: Water stored above a dam
* Energy conversion: Gravitational potential energy ⟶ Electrical energy
* Framework: Turbines
27
What are the advantages and disadvantages of hydroelectric power stations?
**Advantages:**
1. Renewable
2. Clean (no direct emissions)
3. No fuel costs
**Disadvantages:**
1. Low output energy relative to dam size
2. Site‑limited
28
How do hydroelectric power stations generate electricity?
They gravitational potential energy of water stored at a high height is converted to kinetic energy as the water falls which transfers to kinetic energy in the moving turbines that drive generators.
29
What resources, energy conversion process, and framework are used in wind stations?
* Resource: Fast‑moving winds
* Energy conversion: Kinetic energy ⟶ Electrical energy
* Framework: Turbines
30
What are the advantages and disadvantages of wind power stations?
**Advantages:**
1. Renewable
2. Clean (no direct emissions)
3. No fuel costs
**Disadvantages:**
1. Low output energy per turbine
2. Needs consistently windy sites
3. Noise & large land footprint
31
How is wind energy converted into electricity?
The kinetic energy of moving air turns turbine blades, which drive a generator.
32
What resources, energy conversion process, and framework are used in solar stations?
* Resource: Sunlight
* Energy conversion: Light energy ⟶ Electrical energy
* Framework: Solar panels
33
What are the advantages and disadvantages of solar power stations?
**Advantages:**
1. Renewable
2. Clean (no direct emissions)
3. No fuel costs
**Disadvantages:**
1. Low output per panel
2. Weather‑dependent (sunshine variable)
3. Large area required
34
What resources, energy conversion process, and framework are used in wave/tidal stations?
* Resource: Ocean waves & tidal changes (moon’s pull)
* Energy conversion: Kinetic energy ⟶ Electrical energy
* Framework: Turbines
35
What are the advantages and disadvantages of wave/tidal power stations?
**Advantages:**
1. Renewable
2. Clean (no direct emissions)
3. No fuel costs
**Disadvantages:**
1. Very low output energy
2. Few suitable sites (needs high waves)
3. Technologically challenging
36
What resources, energy conversion process, and framework are used in biomass stations?
* Resource: Organic wastes
* Energy conversion: Chemical energy ⟶ Electrical energy
* Framework: Thermal power stations
37
What are the advantages and disadvantages of biomass power stations?
**Advantages:**
1. Renewable
**Disadvantages:**
1. Increases pollution → global warming
2. Requires large land area
38
Which stations use boiling water, which use water without boiling, and which have no moving parts?
**Boiling‑water (thermal) stations:**
* Geothermal, Fossil, Nuclear, Biomass
**Water‑driven (non‑boiling) stations:**
* Hydroelectric, Tidal, Wave
**No moving parts:**
* Solar
39
What defines renewable vs. non‑renewable energy, and which stations don’t originate from the sun?
**Renewable:**
* Never runs out; can be reused
* Examples: Solar, Wind, Geothermal, Tidal, Biomass, Wave, Hydroelectric
**Non‑renewable:**
* Runs out; single‑use only
* Examples: Fossil, Nuclear
**Non‑sun‑derived stations:**
* Tidal, Geothermal, Nuclear
40
How does biomass generate electricity?
The chemical energy in organic materials (like wood or waste) is released by burning, producing steam to drive a turbine and generator.
41
What is linear momentum, and what is its formula?
Momentum is mass × velocity. Formula: **P = m × v**
42
What are the units of momentum?
kg·m/s
43
How do we calculate the change in momentum (when in same and opposite directions)?
* If momentum is in the same direction: ΔP = m(v - u)
* If momentum is in opposite directions or changes direction: ΔP = m(v - (-u)) = m(v + u)
44
How is force related to change in momentum?
F = ΔP / t or F = m (v - u) / t
45
What is impulse?
Impulse is equal to change in momentum (ΔP) or Force × Time of contact
46
What does the law of conservation of momentum state?
Total momentum before a collision = Total momentum after a collision
In a closed system where no external forces act
47
What are the types of collisions?
* Elastic collision: KE is conserved **(m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂)**
* Perfect inelastic collision: Objects stick together; KE is lost **(m₁u₁ + m₂u₂ = V(m₁ + m₂)**
* If object rebounds then whole of that momentum is negative:
**m₁u₁ + m₂u₂ = -(m₁v₁) + m₂v₂**
**m₁u₁ + m₂u₂ = -[V(m₁ + m₂)]**
48
How does conservation of momentum apply to rockets?
Before launch, momentum of fuel and rocket is zero. When fuel burns, it gains a downward momentum so the rocket gains an equal and opposite momentum upwards, making the rocket lift off.
49
How does conservation of momentum apply to a rifle and bullet?
At first, the rifle and bullet have a momentum of 0. When a bullet is fired forward it gains forward momentum, so the rifle recoils and gains equal and opposite backward momentum.
50
How is efficiency defined in energy systems?
Efficiency is the ratio of useful output energy (or work) to the input energy, expressed as a percentage:
* Efficiency = (Useful output energy / Input energy)×100%
51
What is the relationship between impulse and momentum?
Impulse, defined as force multiplied by the time of contact (Impulse = F × t), equals the change in momentum of an object (ΔP). Momentum is a vector quantity given by mass times velocity.
52
Chapter 5: Thermal Physics
53
What are the three states of matter?
Solid, Liquid, Gas
54
How are molecules arranged in solids, liquids, and gases?
* Solids: Regular arrangement, closely packed
* Liquids: Irregular arrangement, close together
* Gases: Irregular arrangement, far apart
55
How does intermolecular distance change across states of matter?
* Solids: Molecules are closely packed
* Liquids: Molecules are close together
* Gases: Molecules are far apart
56
How does intermolecular force compare in different states?
* Solids: Very strong
* Liquids: Strong
* Gases: Very weak
57
Which states of matter are compressible?
Only gases are compressible; solids and liquids are incompressible.
58
How does motion differ between solids, liquids, and gases?
* Solids: Vibrate in fixed positions
* Liquids: Pass by each other
* Gases: Move randomly and freely
| Say "liquid molecules move in clusters" when describing their movement
59
Why are solids and liquids incompressible while gases are compressible?
* Solids: Molecules are tightly packed with strong forces.
* Liquids: Molecules are close together with strong forces.
* Gases: Molecules are far apart with weak forces, allowing compression.
60
What is Brownian motion?
The random movement of microscopic dust/pollen (particles) suspended in a fluid due to collisions with fast-moving molecules in the fluid.
61
What happens to a dust particle in air when observed under a microscope?
It moves freely and randomly in a zigzag path and is seen as a speck of light.
62
Why does Brownian motion occur?
Fast-moving air molecules hit the dust particle from all directions, causing random motion.
63
How does expansion compare in solids, liquids, and gases?
Expansion in solids < Expansion in liquids < Expansion in gases.
64
Explain, in terms of forces between molecules, why gasses expand more than liquids when they have the same rise in temperature
As temperature increases, particles gain kinetic energy and move further apart. For gases, the **average** distance between molecules is greater AND they have weaker intermolecular forces than solids, so they can easily move further apart than solids.
(2 mark question, describe solids explicitly for more marks)
65
What happens to a bimetallic strip when heated?
It bends towards the metal with lower expansion.
66
Give two disadvantages of expansion.
* Expansion in train railways
* Expansion in electric cables
67
What is Boyle’s Law?
At constant temperature, pressure is inversely proportional to volume
**P₁V₁ = P₂V₂**
68
What happens to gas pressure when volume decreases?
Pressure is inversly proportional to volume. As volume decreases , pressure increases because the average distance between the molecules is lower causing the molecules to collide more frequently with container walls and rebound causing a change in momentum which exerts more force and pressure.
| ALWAYS state the relationship between both factors
69
What is the relationship between pressure and temperature at constant volume?
Pressure is directly proportional to temperature.
70
What happens to the pressure of a gas when temperature increases?
Temperature and pressure are directly proportional. As temperature increases, molecules gain kinetic energy, move faster, and collide more frequently and rebound causing a change in momentum which exerts more force and pressure.
| ALWAYS state the relationship between both factors
71
What is the relationship between volume and temperature at constant pressure?
Volume is directly proportional to temperature.
72
What happens to the volume of a gas when its temperature is increased
Temperature and volume are directly proportional. As temperature increases, particles gain kinetic energy and move faster, away from each other, so average distance between molecules increases so volume increases.
73
How do air molecules exert pressure on container walls?
Randomly and freely moving air molecules collide with the walls of the cylinder and rebound causing a change in momentum, which exerts force and pressure
74
What is the formula for heat energy?
Q = mcΔT
where:
* Q = Energy (Joules)
* m = Mass (kg or g)
* c = Specific heat capacity (J/kg°C | J/g°C)
* ΔT = Temperature change (°C)
75
What is thermal capacity?
The amount of energy needed to raise the temperature of a body by 1°C.
76
What must be equal to accurately compare thermal capacities of two different substances?
When comparing between the thermal capacities of different substances make sure that the **energy supplied to both substances is equal**
77
What is specific heat capacity?
The amount of energy required to raise the temperature of **1 kg/g** of a substance by 1°C.
78
Which specific heat capacity is always larger: calculated or actual? And why?
Calculated specific heat is always higher than actual specific heat, as Q and C are proportional so when there are heat losses to the surroundings Q decreases and thus C decreases as well
79
Why do materials with high thermal capacity take longer to heat or cool?
They require more energy to change temperature.
80
How do you calculate thermal capacity from specific heat capacity?
Cₜ (thermal capacity) = c x m
81
What happens to kinetic and potential energy during a temperature change?
* Kinetic energy increases
* Potential energy remains constant
82
What happens to kinetic and potential energy during a change in state?
* Kinetic energy (temperature) remains constant
* Potential energy increases (for melting/boiling) or decreases (for condensation/freezing)
83
What is a boiling/melting point
The temperature at which liquid converts to gas/solid converts to a liquid (at a fixed temperature)
84
Define absolute zero
The lowest possible temperature (−273 °C / 0°K), where the particles have least kinetic energy
| Not "No kinetic energy"
85
How do you convert from celcius to kelvin?
K = C + 273
| 0°K = -273°C
86
Why does evaporation cause cooling?
The most energetic surface molecules absorb energy from remaining liquid, leaving the remaining liquid with less average kinetic energy which decreases temperature
87
How can you increase the rate of evaporation?
* Increase temperature
* Increase air flow
* Increase surface area
* Decrease humidity
* Decrease liquid depth
88
How does heat transfer occur in metals?
Thermal energy is transferred through metals by conduction. This is due to collisions between vibrating atoms and free electrons through atoms going from the hot to cold part
89
What materials are good conductors and why?
Metals (e.g., copper, aluminum) because they have many free electrons.
90
How can conduction be reduced?
Using insulators like plastic, wood, and rubber.
91
In what states of matter does convection occur?
In liquids and gases.
92
Why does hot air rise?
It has lower density and is replaced by cooler, denser air.
93
What is a sea breeze?
Cool air from the sea replaces warm air rising from land.
94
What is a land breeze?
Cool air from land replaces warm air rising from the sea.
95
How can heat loss by convection be reduced?
* Using a vacuum
* Using insulators
* Trapping air between layers
* Using a lid
96
How does radiation transfer heat?
Through electromagnetic (infrared) waves, even in a vacuum.
97
What are good absorbers of radiation?
Dark, dull, rough, black surfaces.
98
What are good reflectors of radiation?
Shiny, polished, white, and silver surfaces.
99
What is the greenhouse effect?
Greenhouse gases trap infrared radiation, increasing Earth's temperature.
100
How can Earth's temperature remain stable?
Incoming radiation from space = Outgoing radiation from Earth.
101
How does a car radiator lose heat?
1. Heat transfers from engine to fluid by conduction.
2. Heat transfers from fluid to radiator by conduction.
3. The radiator is black with a large surface area to increase radiation emission.
102
How does a vacuum flask prevent heat loss?
* Double walls with vacuum: Reduces conduction & convection.
* Silvered walls: Reduces radiation loss.
* Lid: Reduces heat loss by convection.
103
What is the difference between specific heat capacity and thermal capacity?
* Specific heat capacity is the energy required to raise the temperature of 1 kg (or 1 g) of a substance by 1°C,
* Thermal capacity is the total energy needed to raise the temperature of an object by 1°C (specific heat capacity multiplied by its mass).
104
What are the three primary modes of heat transfer, and what is a key characteristic of each?
* Conduction: Energy transfer via direct collisions between particles (depends on thermal conductivity).
* Convection: Energy transfer through the bulk movement of fluids (driven by density differences).
* Radiation: Energy transfer via electromagnetic waves (does not require a medium).
105
How do pressure, volume, and temperature relate in an ideal gas (for constant T, V, or P)?
* At constant temperature (Boyle’s Law): 𝑃 ∝ 1/𝑉
* At constant volume: 𝑃 ∝ 𝑇
* At constant pressure: 𝑉 ∝ 𝑇
106
Why does the temperature remain constant during a phase change even though energy is transferred?
During a phase change, the energy is used to break or form intermolecular bonds rather than increasing the kinetic energy of the particles, so the temperature remains constant until the phase change is complete.
107
Chapter 6: Waves
108
What is a wave, and what are its types?
A wave is a disturbance that transfers energy through a medium.
* Mechanical waves: Need a medium, cannot travel through a vacuum (e.g., sound waves, water waves, P-waves).
* Electromagnetic waves: Do not need a medium, can travel through a vacuum (e.g., light waves, radio waves).
109
What are transverse waves, and how do they differ from longitudinal waves?
* Transverse waves: Particles vibrate perpendicular to wave propagation, consist of crests and troughs (e.g., all waves except sound and P-waves).
* Longitudinal waves: Particles vibrate parallel to wave propagation, consist of compressions and rarefactions (e.g., sound waves, P-waves).
110
What happens during compression and rarefaction in longitudinal waves?
* Compression: Particles are closer, higher pressure.
* Rarefaction: Particles are farther apart, lower pressure .
111
What is amplitude, and what are its units?
* Amplitude (A) is the maximum displacement from the rest position.
* Measured in mm, cm, or m.
112
What is wavelength (λ), and how is it measured in different types of waves?
* Wavelength is the distance between two successive crests/troughs (transverse) or two successive compressions/rarefactions (longitudinal).
* Formula: λ = total distance / number of waves.
113
What is frequency (f), and how is it calculated?
* Frequency is the number of waves that pass in one second.
* Formula: f = number of waves / total time.
* Unit: Hertz (Hz).
* Depends solely on the source of the waves.
114
What is periodic time (T), and how is it related to frequency?
* The time required for one complete wave.
* Formula: T = 1 / f or T = total time / number of waves.
115
What is wave speed (V), and how is it calculated?
* The speed at which a wave travels.
* Formula: V = λf or V = λ / T.
116
What are the laws of reflection?
* Angle of incidence = Angle of reflection.
* Angle of incidence: Between the incident ray and the normal.
* Angle of reflection: Between the reflected ray and the normal.
117
What is refraction, and how does a wave behave when moving between different mediums?
Refraction is the change in direction of a wave due to a change in speed and wavelength when moving between mediums.
* Deep to shallow / rarer to denser: Bends toward the normal, speed and wavelength decrease, frequency remains constant.
* Shallow to deep / denser to rarer: Bends away from the normal, speed and wavelength increase, frequency remains constant.
118
What is a wavefront, and what are its types?
* A wavefront is a surface where all points have the same wave properties.
* Types: Plane or spherical.
119
What are the properties of sound waves?
* Mechanical and longitudinal waves.
* Need a medium to transfer (cannot travel through a vacuum).
* Consist of compressions and rarefactions.
120
How does the speed of sound vary in different states of matter?
**Solids > Liquids > Gases**
* Gases: 100-900 m/s | Air: 320-340 m/s
* Liquids: 1000-2000 m/s | Water: 1500 m/s
* Solids: 2000+ m/s | Steel: 5000 m/s
121
How can the speed of sound be measured using the gun and smoke method?
1. Fire a pistol and start the stopwatch when smoke is seen.
2. Stop timing when the sound is heard.
3. Measure the distance, repeat for accuracy, and calculate speed using distance/time.
122
How can the speed of sound be measured using the echo method?
1. Produce a sound and time the delay until it is heard again.
2. Measure the distance to the reflecting surface.
3. Calculate speed using **(2 × distance) / time.**
123
How can the accuracy of speed of sound experiments be improved?
* Use a larger distance between observers.
* Repeat and take an average.
124
How is loudness related to amplitude?
* Amplitude is proportional to loudness: larger amplitude → louder sound.
* Loud sounds have narrower compressions and wider rarefactions.
125
How is pitch related to frequency?
* Frequency is proportional to pitch: higher frequency → higher pitch.
* Higher pitch means more compressions and rarefactions in a given time.
126
What are the frequency ranges of sound waves?
* Infrasonic: f < 20 Hz.
* Audible for humans: 20 Hz to 20,000 Hz (20 kHz).
* Ultrasonic: f > 20,000 Hz.
127
When a wave passes from one medium to another, which property remains constant and why?
* The frequency remains constant because it is solely determined by the source
* Only the wave’s speed and wavelength change during refraction.
128
Under what condition does significant diffraction occur for a wave passing through a slit?
Diffraction is most pronounced when the slit width is significantly smaller to the wavelength of the wave, allowing the wave to spread out.
129
How does temperature affect the speed of sound in air?
The speed of sound in air increases with temperature because the air molecules move faster, leading to more rapid energy transfer.
130
Chapter 7: Light
131
What are the main properties of light?
* Light is an electromagnetic wave.
* It does not need a medium to transfer (it can travel through a vacuum).
* It is a transverse wave (energy transfer is perpendicular to wave direction).
* It transfers energy from one point to another.
* It can reflect, refract, and diffract.
* Its speed in air/vacuum is 3×10^8 m/s.
* It consists of 7 colors (ROYGBIV).*
132
What is monochromatic light, and how does it compare to polychromatic light (white light)?
* Monochromatic light has one frequency.
* Polychromatic (white) light contains multiple frequencies (the full ROYGBIV spectrum).
133
State the law of reflection in a plane mirror and list the image properties.
**Law of reflection: Angle of incidence = Angle of reflection.**
Image properties in a plane mirror:
* Upright (erect).
* Same size as the object.
* Virtual image.
* Laterally inverted.
* Distance from object to mirror = distance from mirror to image.
134
What is the difference between a real image and a virtual image?
* Real image: Can be formed on a screen; formed by actual rays coming from the object.
* Virtual image: Cannot be formed on a screen; formed by rays that only appear to come from the object.
135
Define refraction and explain why it occurs.
* Refraction is the change in direction of a wave as it passes from one medium to another.
* It happens because the wave’s speed and wavelength change in the new medium, causing the direction to bend.
136
What is Snell’s law for refraction from air to a medium and from a medium to air?
* Air to medium: **𝑛 = sin(𝑖) / sin (𝑟)**
* Medium to air: **𝑛 = sin(𝑟) / sin (𝑖)**
137
Define the terms 𝑖, 𝑟, and 𝑛, and explain how to calculate 𝑛 in terms of speeds
* 𝑖 = angle of incidence.
* 𝑟 = angle of refraction.
* 𝑛 = refractive index, which is the ratio: speed of light in air / speed of light in medium
* A medium with a higher 𝑛 has lower light speed.
* In formula form: 𝑛 = (3×10^8) / 𝑣
138
What happens when light passes from air (rarer) into a denser medium (Case 1)?
* 𝑛(1) < 𝑛(2) and 𝑣(1) > 𝑣(2) || (fast to slow).
* The ray bends towards the normal (𝑖 > 𝑟)
* Use 𝑛 = sin(𝑖) / sin(𝑟)
.
139
What happens when light passes from a denser medium into air (rarer) (Case 2)?
* 𝑛(1) > 𝑛(2) and 𝑣(1) < 𝑣(2) || (slow to fast).
* The ray bends away from the normal (𝑖 < 𝑟)
* Use 𝑛 = sin(𝑟) / sin(𝑖)
140
What is the critical angle (Case 3) and how is it defined?
* The critical angle 𝑐 is the angle of incidence in a denser medium that produces a 90° angle of refraction in air (𝑟 = 90∘).
* 𝑖 = 𝑐: means the refracted ray just grazes the surface.
* 𝑛 = 1 / sin(𝑐)
141
Explain total internal reflection (Case 4) and when it occurs.
* Total internal reflection (TIR) happens when 𝑖 > 𝑐 (angle of incidence is greater than the critical angle) and light travels from a denser medium to a rarer medium.
* All light is reflected inside; no refraction leaves the medium.
142
What occurs when a light ray passes normally (i = 0°) to a surface (Case 5)?
The ray travels straight through without bending because there is no angle of incidence.
143
How do a reflecting prism and a parallel glass plate affect light rays?
* Reflecting prism: Can use total internal reflection or angled reflection (e.g., in a periscope) to change the light path.
* Parallel glass plate: The angle of incidence on the first surface equals the emerging angle from the second surface, making **the incident ray parallel to the emerging ray.**
144
What is special about a semicircular glass plate in refraction experiments?
Any ray incident on the curved (semicircular) surface at its center enters normally (Case 5), so it passes straight through without deviation.
145
How do optical fibres use total internal reflection?
* Optical fibres have a high 𝑛 interior layer and lower 𝑛 exterior layer.
* Light entering at suitable angles reflects internally (TIR) along the fibre without escaping.
* Works with infrared and visible light
146
How are optical fibres used in medicine?
* They are used in endoscopes for medical imaging.
* A fibre is inserted into a blood vessel or body cavity to reach an organ.
* Light travels inside the fibre by TIR to illuminate the organ and returns the image by TIR to a screen.
147
How are optical fibres used in communication?
* They carry telephone, internet, and TV signals at high data rates with more security over longer distances.
* TIR ensures minimal signal loss.
148
What is dispersion of light, and what happens to white light in this process?
* Dispersion is the splitting of white (polychromatic) light into its 7-color spectrum (ROYGBIV).
* Different wavelengths refract by different amounts, causing the colors to separate.
149
Which color has the longest wavelength and highest speed in a medium, and what does that cause?
* Red has the longest wavelength and thus the highest speed in a medium.
* It refracts the least and emerges first in dispersion (ROYGBIV order).
150
What is a convex (converging) lens, and how do you construct its ray diagrams?
A convex lens bends light rays inward, focusing them.
**Ray diagram steps:**
1. A ray parallel to the principal axis refracts through the focus.
2. A ray through the center of the lens continues undeviated.
3. A ray through the focus refracts parallel to the principal axis.
151
What is near-sightedness (short sight), and how is it corrected?
* A near-sighted person can see near objects clearly but not far objects.
* The image forms in front of the retina.
* It is corrected with a diverging (concave) lens.
152
What is far-sightedness (long sight), and how is it corrected?
* A far-sighted person can see far objects clearly but not near objects.
* The image forms behind the retina.
* It is corrected with a converging (convex) lens.
153
List the common properties of all electromagnetic waves.
* They travel at the speed of light in vacuum (3×10^8 m/s).
* They can propagate through a vacuum (no medium required).
* They are transverse waves.
154
What is the order of the electromagnetic spectrum from longest to shortest wavelength?
Radio waves → Microwaves → Infrared (IR) → Visible light → Ultraviolet (UV) → X-rays → Gamma (γ) rays.
155
How are radio waves used, and why can they pass through walls easily?
* Radio waves are used in non-satellite communications (TV, radio) and Bluetooth.
* Their long wavelength and low frequency let them penetrate walls.
156
How are microwaves used, and what adverse effect can they have?
* Uses: Cooking (microwave ovens), satellite communications, mobile phones.
* Adverse effect: Heating effect on tissues.
157
What are the uses and adverse effects of infrared (IR)?
* Uses: Remote controls, security alarm systems, night vision cameras.
* Adverse effect: Can cause skin burns.
158
What are the uses and adverse effects of ultraviolet (UV) radiation?
* Uses: Sterilization of medical equipment, hot missile tracking, security marking, sterilization of water.
* Adverse effects: Skin cancer, blindness/damage to retina.
159
How are X-rays and gamma (γ) rays used, and what are their adverse effects?
* X-rays: Bone photography, airport security, detecting hidden weapons.
* Gamma rays: Security systems, special cameras, sterilization of food, treating cancer
* Both: Can cause cancer, mutations, and kill cells.
160
What is the difference between analogue and digital signals, and why are digital signals advantageous?
* Analogue signals: Continuous variation, prone to noise.
* Digital signals: Two-step voltages (0 = low, 1 = high), can be regenerated accurately, reduce noise, allow higher data transfer rates, and can be converted from analogue.
161
What is diffraction, and when is it most significant?
* Diffraction is the spreading of waves when they pass through a gap or around an obstacle.
* It is most significant when the gap size is similar to the wavelength.
* Longer wavelengths (e.g., radio waves) diffract more than shorter ones (e.g., light).
162
What is white light composed of, and how does dispersion separate it?
* White light is a combination of all visible colours (ROYGBIV).
* Dispersion occurs because different wavelengths refract by different amounts when passing through a prism.
163
Describe how light behaves when it refracts from air into a denser medium.
When light passes from air to a denser medium, its speed decreases, the wavelength shortens, and it bends towards the normal, **while its frequency remains constant.**
164
Which type of lens is used for near-sightedness (myopia) and why?
A diverging (concave) lens is used to correct near-sightedness **because it moves the image from in front of the retina onto it.**
165
What is the standard method for drawing ray diagrams for lenses?
* Draw one ray parallel to the principal axis (which refracts through the focal point)
* Draw one ray through the centre (which is undeviated)
* Draw one ray through the focal point (which refracts parallel to the principal axis)
166
What are the advantages of digital signals over analogue signals in communication systems?
Digital signals are less prone to noise, can be regenerated without quality loss, and support higher data transfer rates, leading to more reliable long-distance communication.
