Class 12 Science Viva

Ohm's law and resistance per unit length of a wire: V-I graph, slope as resistance, why the current must be kept small, rheostat and key positions, least count of the ammeter and voltmeter used · Metre bridge for an unknown resistance and specific resistance, and for verifying series and parallel combination: Wheatstone principle and the balance condition, why the jockey is not dragged, end corrections, why the balance point is kept near the middle · Galvanometer figure of merit by the half-deflection method and conversion of a galvanometer into a voltmeter or ammeter: series versus shunt resistance, the formulas used, and verification of the converted instrument · Focal length of a convex lens, concave mirror and convex mirror using a convex lens: u-v and 1/u versus 1/v graphs, sign convention, parallax removal, index correction and why the object is kept beyond the focal length · Angle of minimum deviation versus angle of incidence for a glass prism, and refractive index of a glass slab with a travelling microscope: the i-D curve, the prism formula, real and apparent depth · Forward and reverse bias characteristics of a p-n junction diode: knee voltage of silicon and germanium, dynamic resistance from the graph, why a milliammeter is used in forward and a microammeter in reverse bias, breakdown · Activities and the investigatory project: identifying diodes, LEDs, resistors and capacitors from a mixed collection, assembling a household circuit, the mirror or lens activities, and the physics behind the student's own project · Errors, least count, significant figures and graph practice: why readings are repeated, mean and percentage error, choosing a scale, drawing the best-fit line and reading a slope with units

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Volumetric analysis with potassium permanganate: standardising against oxalic acid or Mohr's salt, why KMnO4 is self-indicating and kept in the burette, why oxalic acid is warmed to about sixty degrees while Mohr's salt is not, role of dilute sulphuric acid, normality and molarity calculations · Qualitative analysis of a simple salt, cations: preliminary tests, group separation with dilute HCl, H2S, NH4Cl and NH4OH, ammonium sulphide and ammonium carbonate, confirmatory tests for the group cations such as the Prussian blue test for Fe3+, the ash test for Al3+, and flame tests for Ca2+, Sr2+ and Ba2+ · Qualitative analysis of a simple salt, anions: dilute and concentrated sulphuric acid groups, ring test for nitrate, chromyl chloride test for chloride, layer test for bromide and iodide, barium chloride for sulphate, the acetate and oxalate tests, and the chemistry of each colour or gas observed · Tests for organic functional groups: unsaturation with bromine water and Baeyer's reagent, alcoholic with ceric ammonium nitrate, phenolic with neutral FeCl3, aldehyde versus ketone with Tollens', Fehling's and 2,4-DNP, carboxylic with sodium bicarbonate, amino with carbylamine and azo-dye tests · Tests for carbohydrates, fats and proteins in pure samples and foodstuffs: Molisch, Fehling's and Benedict's, iodine for starch, translucent-spot and acrolein tests for fats, biuret, ninhydrin and xanthoproteic for proteins · Content-based experiments: effect of concentration and temperature on the rate of the thiosulphate-HCl reaction, enthalpy of dissolution of copper sulphate or potassium nitrate and enthalpy of neutralisation, variation of EMF of a zinc-copper Daniell cell with concentration, paper chromatography of pigments and Rf values, preparation of ferrous ammonium sulphate, potash alum, acetanilide or dibenzalacetone · Laboratory safety and technique: handling concentrated acids and H2S, reading a burette and rinsing versus not rinsing the pipette and burette, why the first drop is discarded, disposal of chemicals, and what to do when a reagent splashes · Investigatory project chemistry: the principle behind common projects such as adulterants in food, acidity of tea or soft drinks, rate of fermentation, casein in milk, and how the student designed controls and recorded data

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Temporary slide preparation and identification of stages of mitosis in onion root tip: pre-treatment with HCl, acetocarmine staining, squash technique, how prophase, metaphase, anaphase and telophase are recognised, and why the root tip is used · Pollen germination on a slide in sucrose and boric acid solution: what the pollen tube is, role of boric acid, percentage germination, and flowers adapted to pollination by wind, water, insects and birds and their characteristics · Soil and water studies: pH of different soil samples, water-holding capacity, texture and moisture content, dissolved oxygen, turbidity, pH and living organisms in water from different sites, and how these affect plant growth · Ecology by quadrat: population density and frequency of plant species in a field or lawn, the formulas, how quadrats are placed, and the difference between density, frequency and abundance · Spotting of prepared slides, specimens and charts: stages of meiosis, T.S. of blastula, T.S. of testis and ovary, pedigree charts for traits such as colour blindness and widow's peak, Mendelian inheritance with seeds or beads, homologous and analogous organs, and the disease-causing organisms Ascaris, Entamoeba, Plasmodium and a ringworm fungus · Controlled pollination: emasculation, bagging and tagging, in which flowers it is possible and why, and the relevance to hybrid seed production · Isolation of DNA from spinach, green pea seeds or papaya: role of detergent, salt and chilled ethanol, why the DNA appears as white threads, and the limits of what the crude extract shows · Investigatory project and record: observation versus inference, how the student collected and tabulated data, drew labelled diagrams, cited sources, and the biology behind the project they chose

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Python text, binary and CSV file handling: open modes and the with statement, read, readline and readlines, pickle dump and load, csv.writer and csv.reader, seek and tell, and the difference between text and binary files in storage · Python functions, exceptions and data structures: positional, default and keyword arguments, scope and the global keyword, try-except-finally, implementing a stack with push and pop on a list, and when a dictionary beats a list · SQL on a single table and joins: CREATE, ALTER, INSERT, UPDATE, DELETE, WHERE with LIKE, BETWEEN and IN, aggregate functions with GROUP BY and HAVING, ORDER BY, equi-join and natural join, primary and foreign keys, and the difference between DDL and DML · Python-MySQL connectivity: mysql.connector, connect parameters, cursor, execute, fetchone, fetchall, rowcount, commit, and parameterised queries versus string formatting · For Informatics Practices: Pandas Series and DataFrame creation, indexing with loc and iloc, head and tail, adding and deleting rows and columns, describe, reading and writing CSV, and Matplotlib line, bar and histogram plots with titles, labels and legends · Networking, data and societal awareness as asked in viva: IP address, URL, HTTP versus HTTPS, cookies, the digital footprint, plagiarism, licensing and the IT Act in outline, and for IP the difference between data and information · The practical examination itself: the lab test program and SQL queries, the report file with its minimum programs and query sets, the project with its problem statement, modules, data design, testing and limitations, and demonstrating the project running · Debugging under the examiner's eye: reading an error traceback, off-by-one and indentation errors, what happens on a KeyError or FileNotFoundError, and explaining the output of a given code fragment

15+ seeded questions