Physical Science Last Minute Revision
Quick-fire revision of key reactions, formulas, and facts for AP SSC Class 10 Physical Science (General Science Paper I). Read through this the night before and morning of the BSE AP exam.
Chemistry — Key Reaction Types
- →Combination A+B→AB · Decomposition AB→A+B · Displacement A+BC→AC+B · Double Displacement AB+CD→AD+CB
- →Precipitation = insoluble salt formed; effervescence = gas evolved; colour change = indicator of reaction
- →Corrosion (rusting): 4Fe + 3O₂ + xH₂O → 2Fe₂O₃·xH₂O; prevented by galvanising, painting, alloying
- →Rancidity: oxidation/hydrolysis of fats and oils; prevented by antioxidants, vacuum packing, refrigeration
Acids, Bases and Salts — Must Know
- →Acid + Metal → Salt + H₂↑ · Acid + Base → Salt + H₂O · Acid + CO₃²⁻ → Salt + H₂O + CO₂↑
- →pH < 7 acidic · pH = 7 neutral · pH > 7 basic; litmus turns red in acid, blue in base
- →Dilute acid → always add acid to water (never reverse); generates heat
- →NaOH = lye/caustic soda · Ca(OH)₂ = slaked lime · CaO = quick lime · Na₂CO₃ = washing soda · NaHCO₃ = baking soda
Metals and Non-metals — Reactivity Series
- →K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au — more reactive metals displace less reactive
- →Na + cold water; Mg + steam (not cold water); Fe + steam only; Cu does not react with water at all
- →Thermite: 2Al + Fe₂O₃ → Al₂O₃ + 2Fe (very exothermic; welds railway tracks)
- →Ionic bond: electron transfer; properties — crystalline solid, high melting point, conducts in molten/dissolved state
Carbon Compounds — Quick Recall
- →Alkane CₙH₂ₙ₊₂ (saturated) · Alkene CₙH₂ₙ (one double bond) · Alkyne CₙH₂ₙ₋₂ (one triple bond)
- →Functional groups: −OH (alcohol) · −COOH (acid) · −CHO (aldehyde) · −CO− (ketone) · −NH₂ (amine)
- →Addition (alkene + H₂/Cl₂/HCl) · Substitution (alkane + Cl₂ in sunlight) · Combustion → CO₂ + H₂O
- →Esterification: ethanol + ethanoic acid ⇌ ethyl ethanoate + H₂O (conc. H₂SO₄ catalyst; fruity smell)
Light — Mirror and Lens Formulas
- →Mirror: 1/v + 1/u = 1/f · f = R/2 · m = −v/u · concave: f negative (new Cartesian)
- →Lens: 1/v − 1/u = 1/f · P = 1/f(metres) · convex → +f · concave → −f
- →Real image: formed by actual intersection of rays (can be projected) · Virtual: appears to diverge
- →Snell's law: n₁sinθ₁ = n₂sinθ₂ · n = c/v (denser medium → slower light → larger n)
Human Eye — Defects and Corrections
- →Myopia: far objects blurred; image in FRONT of retina → concave lens; P = −1/far point (metres)
- →Hypermetropia: near objects blurred; image BEHIND retina → convex lens
- →Normal eye: near point 25 cm, far point infinity; accommodation = ability to change focal length
- →Blue sky: Rayleigh scattering (∝ 1/λ⁴); sunset red: blue scattered away, only red/orange reaches eye
Electricity — Formulas Quick Fire
- →V = IR · R = ρl/A · Series: R_total = R₁+R₂+... · Parallel: 1/R = 1/R₁+1/R₂+...
- →P = VI = I²R = V²/R · H = I²Rt (Joule's law) · E = Pt = VIt
- →1 kWh = 3.6 × 10⁶ J · Cost = Power(kW) × Time(h) × Rate(₹/unit)
- →Fuse: low melting point alloy; breaks circuit on overloading; placed in LIVE wire
Magnetism and EM Induction — Key Points
- →Right-hand thumb rule: current → B field direction around straight wire
- →Fleming's Left-Hand Rule: force on conductor (motor) · Fleming's Right-Hand Rule: induced current direction (generator)
- →Transformer: V_s/V_p = N_s/N_p = I_p/I_s · step-up: N_s > N_p · step-down: N_s < N_p
- →AC in India: 220 V (rms), 50 Hz · domestic wiring: live (red), neutral (black), earth (green)
Exam Day Strategy
- →Attempt Section I (1-mark) first — 8 marks × 1, no steps needed; do NOT skip any
- →Section II (2-mark): write reaction equation + one observation; diagrams score marks even if labels incomplete
- →Section III (4-mark): numericals — write given, formula, substitution, answer with units; 1 mark per step
- →Section IV (8-mark) essay: write in points, not paragraphs; use sub-headings; draw neat labelled diagram