Comprehensive Grade 11 Science Notes – Heat, Electricity, Electronics, Chemistry, Ecology

Heat

9.1 Temperature

• Temperature = quantitative measure of mean kinetic energy of particles in a substance.
• Historical thermometers: Galileo’s early thermoscope (~1600 AD).
• Three common temperature scales
  • Celsius (°C): 0 °C = ice–water equilibrium; 100 °C = boiling water at 1 atm.
  • Fahrenheit (°F): $32\,^{\circ}\text{F}$ melting ice; $212\,^{\circ}\text{F}$ boiling water; 180 equal divisions.
  • Kelvin (K): absolute scale; 0 K = absolute zero $(-273.15\,^{\circ}\text{C})$; size of 1 K = 1 °C.
• Relationship: $T<em>{\text{(K)}} = t</em>{\text{(°C)}} + 273$.
• Types of thermometers
  • Glass–mercury (uniform expansion, toxic).
  • Glass–alcohol (measures down to $-115^{\circ}\text{C}$, dyed for visibility).
  • Digital (use temperature–dependent electrical property such as resistance).

9.2 Heat

• Heat = energy that flows from higher-T body to lower-T body owing to temperature difference.
• Thermal equilibrium: state when bodies in contact reach same temperature; net heat flow = 0.
• SI unit: joule (J); practical non-SI: calorie; $1\,\text{cal}=4.186\,\text{J}$.

Heat Capacity (C)

• $C = \dfrac{\text{Heat required}}{\text{Temperature rise}}$, units J K⁻¹ (or J °С⁻¹).

Specific Heat Capacity (c)

• Heat needed to raise temperature of 1 kg by 1 K/°C.
• Units $\text{J kg}^{-1}\,\text{K}^{-1}$.
• Relation: $C = mc$.
• Heat transfer equation: $Q = mc\theta$ where $\theta$ = temperature change.

Worked example

• Raise 2 kg water by 10 K: $Q = 2\times 4200 \times 10 = 8.4\times10^{4}\,\text{J}$.

9.3 Change of State & Latent Heat

• Melting point = °C at which solid → liquid under 1 atm; equal to freezing point.
• Boiling point = °C at which liquid forms bubbles (1 atm).
• Latent heat: energy absorbed/released at constant T during phase change.
• Specific latent heat of fusion (ice): $3.36\times10^{5}\,\text{J kg}^{-1}$.
• Specific latent heat of vaporisation (water): $2.26\times10^{6}\,\text{J kg}^{-1}$.
• Evaporation vs. boiling: evaporation at any T < b.p.; takes place at surface only.

9.4 Thermal Expansion

• Solids, liquids, gases expand on heating, contract on cooling.
• Applications/precautions
  • Railway gaps, overhead cables sag, bimetal strips in thermostats, tyre rims on cart wheels.

9.5 Heat Transfer

• Three modes: Conduction (solids), Convection (fluids), Radiation (no medium).
• Conductors vs. insulators; role of free electrons in metals.
• Convection currents: sea breeze (day), land breeze (night).
• Radiation: electromagnetic waves; darker/rough = good absorbers; shiny/white = good reflectors.

Power and Energy of Electric Appliances

10.1 Electric Power

• $P = VI$ (W) for appliance with supply V & current I.

10.2 Electrical Energy

• $E = Pt = VIt$ (J). Commercial unit: kilowatt-hour (kWh).
• $1\,\text{kWh}=3.6\times10^{6}\,\text{J}$.

10.3 Efficiency & Conservation

• Efficiency %= $\dfrac{\text{Useful output}}{\text{Input}}\times100$.
• CFL / LED bulbs, induction cookers, microwave ovens: higher efficiency than filament lamps, coil stoves.

10.4 Home Electrical Circuit

• Supply: 230 V, 50 Hz AC via live (L) & neutral (N).
• Protective devices: overload circuit breaker/service fuse (≈40 A), isolator (main double-pole switch), RCCB (trip; 30 mA leakage), MCBs (6 A lighting, 13 A socket).
• Ring & radial circuits; all switches in live line; 3-pin sockets connect earth.

10.5 Metering & Billing

• kWh meter records consumption.
• kWh = (W÷1000)×h.

Electronics

11.1 Semiconductors

• Intrinsic (pure Si or Ge): covalent lattice; electrons & holes equal; conductivity ↑ with T.
• Extrinsic via doping
  • n-type: add group V donor (P, As); extra electrons.
  • p-type: add group III acceptor (B, Al); create holes.

11.2 p–n Junction

• Depletion layer forms; potential barrier ≈ $0.7\,\text{V (Si)},\;0.3\,\text{V (Ge)}$.
• Biasing
  • Forward: p to +, n to −; barrier reduced → current.
  • Reverse: p to −, n to +; barrier widens → tiny leakage.

11.3 Diode

• Allows current one way. Symbol: triangle-bar.
• Light Emitting Diode (LED): GaAs, GaN etc.; forward V$_{min}$ ≈ 1.8 V (red) to 5 V (blue); long life 50 000 h.
• Solar cell = illuminated p-n junction; converts light to DC.

11.4 Rectification

• Half-wave: single diode + load.
• Full-wave: bridge of 4 diodes—both half-cycles same polarity.
• Smoothing: large capacitor across load reduces ripple.

11.5 Transistor (npn / pnp)

• Terminals: Emitter (E), Base (B), Collector (C).
• Bias: E–B forward (~0.7 V), C–B reverse (≥ +5 V for npn).
• Applications
  • Current amplifier: small IB controls large IC.
  • Switch: off when VBE
  • Audio amplification (common-emitter).

Electrochemistry

12.1 Electrochemical Cells

• Simple Zn–Cu cell in $H<em>2SO</em>4$:
  • Anode (−): $\text{Zn}\rightarrow\text{Zn}^{2+}+2e^-$ (oxidation).
  • Cathode (+): $2\text{H}^++2e^-\rightarrow\text{H}_2$.
• Cell EMF from redox reactions.
• Direction: electrons flow anode→cathode; conventional current opposite.

12.2 Electrolysis

• Electrolyte = liquid conducting by ions; requires external DC source.
• At cathode: cations gain electrons (reduction).
• At anode: anions lose electrons or anode metal dissolves (oxidation).
• Examples
  • Fused $NaCl$ (Downs cell): $\text{Na}^+ + e^- \rightarrow \text{Na}$ (l); $2\text{Cl}^- \rightarrow \text{Cl}_2 +2e^-$.
  • Brine electrolysis: produces $Cl<em>2$, $H</em>2$ and $NaOH$.
  • Aqueous $CuSO<em>4$ with carbon: cathode $Cu^{2+}+2e^-\rightarrow Cu$; anode $4OH^-\rightarrow O</em>2+2H_2O+4e^-$.

12.3 Corrosion & Protection

• Rusting: $2Fe + O<em>2 + 2H</em>2O \rightarrow 2Fe(OH)<em>2 \rightarrow Fe</em>2O<em>3·xH</em>2O$.
• Requires $O<em>2$ and $H</em>2O$; accelerated by $Cl^-$, acids.
• Prevention
  • Barrier: paint, grease, tin plating, galvanising (Zn).
  • Sacrificial (cathodic) protection: attach more reactive metal (Zn, Mg).

Electromagnetism & Electromagnetic Induction

13.1 Magnetic Basics

• Magnetic field = region where magnetic force is experienced; direction shown by compass.

13.2 Magnetic Effect of Current

• Right-hand grip / corkscrew rules give field around straight conductor.
• Force on current conductor in field: magnitude $F \propto BIL$; direction via Fleming’s left-hand rule (F-B-I).
• Applications
  • DC motor: armature + split-ring commutator; electric → mechanical.
  • Loudspeaker: voice-coil in magnetic gap vibrates cone.

13.3 Electromagnetic Induction

• Faraday’s law: induced EMF $\propto$ rate of change of magnetic flux linkage $\phi$.
• Fleming’s right-hand rule (motion–field–current) gives polarity.
• Alternator/dynamo: rotating coil in fixed field → sinusoidal EMF.
• Transformer (AC only): $\dfrac{V<em>P}{V</em>S}=\dfrac{N<em>P}{N</em>S}$; ideal power $V<em>PI</em>P=V<em>SI</em>S$.
  • Step-up: $N<em>S>N</em>P$; step-down opposite.
• Other devices: moving-coil microphone, bicycle dynamo.

Hydrocarbons & Derivatives

14.1 Hydrocarbons

• Contain C & H only. Classified by C-C bonding
  • Alkanes $C<em>nH</em>{2n+2}$ (single bonds).
  • Alkenes $C<em>nH</em>{2n}$ (≥1 C=C).
• Examples
  • Methane $CH<em>4$, Ethane $C</em>2H<em>6$, Propane $C</em>3H_8$…

14.2 Derivatives of Ethene

• Chloroethene (vinyl chloride) $C<em>2H</em>3Cl$.
• Tetrafluoroethene $C<em>2F</em>4$.

14.3 Polymers

• Polymer = macromolecule formed by repeated monomer units (polymerisation).
• Addition polymers from alkenes
  • Polyethene: $(CH<em>2-CH</em>2)_n$.
  • PVC: $(CH<em>2-CHCl)</em>n$ from chloroethene.
  • PTFE (Teflon): $(CF<em>2-CF</em>2)_n$ from tetrafluoroethene.
• Natural vs. synthetic polymers; linear, branched, cross-linked; vulcanised rubber = sulphur cross-links.

Biosphere & Ecology

15.1 Organisation & Balance

• Levels: Individual → Population → Community → Ecosystem → Biosphere.
• Population growth shows sigmoid S-curve (lag, log, deceleration, stationary); human growth ~ J-curve.

15.2 Energy & Nutrient Flow

• Trophic levels: producers, primary/secondary/tertiary consumers, decomposers.
• Food chains & webs; only ~10 % energy passed up each level → pyramids of number/biomass/energy.
• Biogeochemical cycles: Carbon cycle (photosynthesis, respiration, combustion); Nitrogen cycle (N-fixation, nitrification, denitrification).

15.3 Pollution & Effects

• Major pollutants: agrochemicals, industrial waste, greenhouse gases (CO₂, CH₄, CFCs), heavy metals (Pb, Cd, Hg), particulates, POPs, e-waste.
• Environmental issues: acid rain, photochemical smog, eutrophication, bio-magnification, ozone depletion, global warming.

15.4 Lifestyle Factors & Health

• Industrialisation, urbanisation, improper food habits → rise in non-communicable diseases (diabetes, CKD, heart disease).
• CKD: linked to heavy metals & agrochemicals; prevention—clean water, minimise chemicals.

15.5 Sustainable Development & Management

• 4 R waste strategy: Reduce, Reuse, Recycle, Replace.
• Traditional agricultural practices: multiple cropping, bio-fertilisers, biological pest control.
• Reforestation; carbon footprint & food miles reduction; energy auditing; renewable energy (solar, wind, biomass).