SOF NSO flashcards
170 cards from 23 fact-checked topic notes · English
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Verbal Reasoning · Key Concepts
Word Analogy
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Verbal Reasoning — Logical Reasoning · 7 cards
- Word Analogy
- Two words are related in a specific way; you must identify another pair with the same relationship. Common types include synonym pairs (happy : joyful), antonym pairs (hot : cold), part-to-whole (wheel : car), worker-to-tool (carpenter : saw), and cause-effect (fire : smoke).
- Classification (Odd One Out)
- Four or five words are given, where all except one belong to the same category. The odd word differs by class, property, or function. For example, in "rose, lotus, sunflower, marigold," lotus is the odd one (aquatic plant, others terrestrial).
- Word Formation
- Given a base word, determine which target words can be formed using only the letters available in the base word, with each letter used at most as many times as it appears. For instance, from "TRANSPORT" you can form "PORT" but not "PASSPORT" (only one 'S' available).
- Letter Frequency Matters
- In word formation, count each letter's occurrence in the base word. If the target word requires more of any letter than available, it cannot be formed.
- Category Recognition
- For classification, quickly identify the unifying category — professions, animals, fruits, metals, abstract nouns, verbs, etc. The odd word will violate this category.
- Relationship Direction
- In analogies, ensure the relationship flows in the same direction. "Doctor : Hospital" relates as worker-to-workplace, so the answer should follow the same pattern, not workplace-to-worker.
- Elimination Strategy
- For classification, eliminate words that clearly share the common property first. The remaining word is your answer. For word formation, eliminate impossible words early by checking for missing or insufficient letters.
Non-Verbal Reasoning — Logical Reasoning · 8 cards
- Figure Pattern Recognition
- Every figure is composed of distinct elements—outer shape, inner elements, shading patterns, line styles, symmetry and orientation. Learn to deconstruct complex figures into these basic attributes systematically.
- Transformation Rules
- Figures change following logical rules—rotation (clockwise/anticlockwise by 90°/180°), reflection (horizontal/vertical flip), size change (enlargement/reduction) or element addition/deletion. One rule or multiple rules may apply simultaneously.
- Series Logic
- In figure series, each step follows a consistent rule. The pattern may involve progressive change (adding one element each time), alternating patterns (ABAB sequence) or cyclic rotation through positions.
- Analogy Relationships
- Figure analogy follows the format A:B::C:D meaning "A is to B as C is to D". The relationship between A and B must be identical to the relationship between C and D. Common relationships include rotation, shape change, element swap or positional shift.
- Classification Principle
- In odd-one-out problems, three or four figures share a common property while one differs. The distinguishing feature could be symmetry, number of sides, type of shading, direction of rotation or any other attribute.
- Element Counting
- Many problems hinge on counting specific elements—number of dots, lines, triangles, intersections or enclosed regions. Systematic counting prevents errors.
- Positional Analysis
- Track how elements move within a figure—clockwise/anticlockwise movement, diagonal shifts, corner-to-center movement or exchange of positions between elements.
- Negative Space Recognition
- Sometimes the answer lies in what's NOT present—missing segments, gaps or spaces between elements form the pattern rather than the solid elements themselves.
Series Completion — Logical Reasoning · 8 cards
- Pattern Recognition
- Every series follows a rule or operation applied consistently across terms. Your job is to decode this rule by examining differences, ratios or transformations between consecutive elements.
- Number Series Operations
- Common patterns include arithmetic progression (constant addition/subtraction), geometric progression (constant multiplication/division), squares/cubes, prime numbers, Fibonacci-style addition (sum of previous two terms), and alternating operations.
- Alphabet Series Logic
- Letters are treated as numbers based on position. Patterns include fixed jumps (+2, +3, etc.), reverse alphabets, skipping letters, or alternating forward/backward movements. Remember Z wraps to A in cyclic patterns.
- Mixed Series
- Some series alternate between two sub-patterns. Example: odd positions follow one rule, even positions follow another. Always separate the series into sub-sequences when simple patterns don't fit.
- Figural Series
- Visual patterns involve rotation (clockwise/anticlockwise), reflection (horizontal/vertical flip), addition/removal of elements, shading changes, or size progression. Count elements systematically.
- Wrong Term Identification
- Sometimes you're given a series with one wrong element. Apply the pattern rule to each position and spot which term breaks it.
- Missing Middle Term
- The blank can appear anywhere in the series, not just at the end. Establish the pattern using complete terms, then apply it to find the missing one.
- Multiple Operations
- Complex series may combine two operations alternately. Example: +3, ×2, +3, ×2... Always test your discovered pattern on all visible transitions.
Analogy — Logical Reasoning · 8 cards
- Basic Analogy Structure
- All analogy questions follow A:B :: C:D format. You're either given three terms and must find the fourth, or you must identify which pair shares the same relationship as a given pair.
- Word Analogy Relationships
- Common patterns include synonyms/antonyms, category-member (animal:lion), part-whole (wheel:car), cause-effect (virus:disease), tool-function (pen:write), and degree (hot:scalding).
- Number Analogy Patterns
- Look for arithmetic operations (addition, subtraction, multiplication, division), square/cube relationships, prime numbers, digit sums, positional values, or sequence patterns between the numbers.
- Figural Analogy Logic
- Identify transformations like rotation, reflection, increase/decrease in elements, shading changes, position shifts, or shape conversions. The relationship applies visually rather than verbally or numerically.
- Multiple Relationships
- Some complex analogies involve two simultaneous relationships. For example, 3:9 :: 4:16 involves both "multiply by itself" and "consecutive integers as bases."
- Elimination Strategy
- When multiple options seem plausible, test each by clearly stating the relationship in words. The correct answer must maintain the exact same logical connection.
- Direction Matters
- In analogies, the order is critical. "Doctor:Hospital" (person:workplace) is different from "Hospital:Doctor" (workplace:person). Always maintain the directional flow of the relationship.
- Common Trap Patterns
- Avoid surface-level connections. Just because two words belong to the same broad category doesn't mean they share the specific relationship needed for analogy completion.
Coding-Decoding — Logical Reasoning · 7 cards
- Letter-Shift Coding
- Each letter moves a fixed number of steps forward or backward in the alphabet. Example: A → D (shift +3), B → E (shift +3). If BOOK codes to ERRN, every letter shifted +3.
- Reverse Alphabet Coding
- Replace each letter with its counterpart from the opposite end. A ↔ Z, B ↔ Y, C ↔ X, and so on. Position formula: (26 – position + 1). If CAT codes to XZG, reverse coding is at work.
- Letter-to-Number Coding
- Assign each letter its alphabet position (A=1, B=2, ... Z=26) and apply arithmetic. Example: If BAD codes to 214, then B=2, A=1, D=4 — direct positional coding.
- Mixed Operations
- Combine shift + reverse, or alternate rules for odd/even positions. Example: First letter +2, second letter –1, third letter +2, repeat. These require careful pattern isolation for each position.
- Word-to-Number Total Coding
- Sum the alphabet positions of all letters. Example: CAT = 3+1+20 = 24. Used less often.
- Substitution Coding
- A consistent cipher where specific letters/symbols replace others throughout. Example: If "ROSE" is coded as "TQUG", check each letter pair: R→T (+2), O→Q (+2), S→U (+2), E→G (+2). Substitution often looks random but follows one hidden rule.
- Conditional Coding
- Rule changes based on letter type (vowel vs consonant) or position (first letter vs others). Example: Vowels shift +1, consonants shift +2. Always test the pattern separately for vowels and consonants if a uniform shift doesn't fit.
Mathematical Operations — Logical Reasoning · 6 cards
- Symbol Substitution
- The problem defines new meanings for standard operators. For example, if "A + B means A ÷ B," you must mentally (or on paper) replace every + with ÷ throughout the expression before calculating.
- BODMAS/BODMAS Rule
- After substitution, evaluate strictly in this order: Brackets, Orders (powers/roots), Division and Multiplication (left to right), Addition and Subtraction (left to right). Ignoring this order is a common cause of wrong answers.
- Four Operation Types
- Problems usually substitute the four basic operations (+, −, ×, ÷) with each other or with symbols like @, #, $, ★. Less common variations include interchange with comparison operators (>, <, =) in "find the true statement" questions.
- Two Question Formats
- (1) Direct evaluation — "If A $ B means A + B and A # B means A × B, find the value of 8 $ 4 # 3." (2) Statement verification — "Which equation becomes true after applying the given substitutions?"
- No Actual Math Complexity
- Once substituted correctly, the arithmetic is typically at Class 5–7 level (whole numbers, simple fractions). The difficulty is procedural, not computational.
- Work Methodically
- Write out the substitution step explicitly in rough work. Never try to substitute and calculate mentally for multi-operator expressions—errors multiply quickly.
Alphabet Test — Logical Reasoning · 7 cards
- Original Alphabet Positions
- The English alphabet has 26 letters. A is at position 1, Z is at position 26. Knowing at least positions of A (1), E (5), J (10), O (15), T (20), Z (26) by heart saves time.
- Left and Right Positions
- "Position from left" means counting A, B, C… forward. "Position from right" means counting Z, Y, X… backward. The same letter has two different positions depending on the direction.
- Complementary Position Rule
- If a letter is at position n from the left, its position from the right is 27 − n. This is the most important formula for this topic.
- Reverse Alphabet
- When the alphabet is written in reverse (Z, Y, X…, A), the letter at position n from the left in the original alphabet moves to position 27 − n from the left in the reversed alphabet.
- Letter Distance
- The distance between two letters is the absolute difference of their positions plus one if counting inclusively, or just the absolute difference if counting gaps.
- Vowels and Consonants
- A, E, I, O, U are vowels (positions 1, 5, 9, 15, 21). The remaining 21 letters are consonants. Some questions filter based on this classification.
- Middle Letter
- The 13th letter (M) and 14th letter (N) are the middle pair. Any letter beyond N (14) is in the second half; before N is in the first half.
Ranking and Order — Logical Reasoning · 7 cards
- Linear Arrangement
- Objects or people arranged in a single line, either horizontal (left to right) or vertical (top to bottom). Each position is unique.
- Rank from Top/Left vs Bottom/Right
- The same person occupies different numerical ranks depending on which end you count from. Understanding this dual perspective is the foundation of all problems.
- Total Elements Formula
- If someone is Rth from one end and Sth from the other end in a line, then Total = R + S - 1. The "-1" accounts for counting the same person twice.
- Conversion Formula
- When total N is known and someone is Rth from top, their rank from bottom = N - R + 1. This works symmetrically in reverse.
- Overlapping Positions
- When two people's positions are given from different ends, you can often determine their relative positions or the minimum total in the line.
- Between Problems
- If someone is between two others, their rank falls strictly inside the range defined by those two positions.
- Interchange Problems
- When two people swap positions, their ranks from both ends exchange. Track the effect on other position-dependent statements.
Blood Relations — Logical Reasoning · 8 cards
- Generation levels matter.
- Always track whether people are in the same generation (siblings, cousins), one generation apart (parent-child), or two apart (grandparent-grandchild). Mixing generations is the fastest route to wrong answers.
- Gender is critical.
- Many relationships change meaning with gender: brother vs sister, uncle vs aunt, grandson vs granddaughter. If gender is not stated, consider both possibilities or look for clues in pronouns (he/she, his/her).
- Paternal vs maternal side.
- Uncle can mean father's brother or mother's brother. Aunt can be father's sister or mother's sister. The prefix "maternal" or "paternal" clarifies, but if omitted, check the problem context.
- Spouse links connect families.
- If A is married to B, then A's parents become B's in-laws, and B's siblings become A's brothers/sisters-in-law. Keep track of marriages to avoid dead ends.
- Use symbols or abbreviations.
- In rough work, draw circles for females, squares or triangles for males, and use lines to show parent-child or marriage links. Or use letters with +/- or M/F labels. Speed comes from a consistent notation system.
- Only-child and sibling clues.
- "Only son" or "only daughter" means no other children of that gender in the family. This narrows possibilities sharply in complex puzzles.
- "My mother's daughter" = me or my sister.
- In pointing problems, always simplify possessive chains step by step. "My mother's daughter" is either the speaker or the speaker's sister, never the mother herself.
- Count carefully in multi-step chains.
- If A is the father of B, and B is the father of C, then A is the grandfather of C — two generations up. Track each link to avoid off-by-one errors.
Direction Sense — Logical Reasoning · 8 cards
- Four cardinal directions
- North (N), South (S), East (E), West (W). North is conventionally at the top of the page; South opposite it; East to the right; West to the left.
- Intermediate directions
- North-East (NE), South-East (SE), South-West (SW), North-West (NW). These lie exactly between the cardinal directions at 45° intervals.
- Opposite directions
- North ↔ South, East ↔ West. Turning 180° from any direction gives the opposite direction.
- Right and left turns
- If you face North and turn right 90°, you face East. If you turn left 90°, you face West. Always visualize yourself facing the current direction before turning.
- Clockwise order of directions
- N → E → S → W → N (four 90° clockwise turns complete a circle). Anti-clockwise is the reverse: N → W → S → E → N.
- Distance calculation
- When movement involves only North-South and East-West legs, the final displacement forms a right triangle. Use the Pythagorean theorem: shortest distance = √(North-South displacement² + East-West displacement²).
- Net displacement
- Add all North movements, subtract all South movements to get net North-South displacement. Do the same for East-West. Displacement is the straight-line distance from start to finish, not the total path traveled.
- Final direction
- After all movements, determine the position relative to the starting point — is the person North of start, South-East, etc.?
Missing Characters — Logical Reasoning · 8 cards
- Row-wise and column-wise operations
- Common patterns involve applying the same arithmetic or logical operation across all rows or all columns. Check if each row follows the same rule independently.
- Diagonal and cross-patterns
- Sometimes the rule connects elements diagonally (top-left to bottom-right) or in a cross shape (e.g., center = sum of corners).
- Alphabetical position substitution
- Letters are often converted to their position in the alphabet (A=1, B=2, …, Z=26), then subjected to arithmetic operations. The answer may be a number or converted back to a letter.
- Constant difference or ratio
- In number sequences, check if moving from one cell to the next involves adding/subtracting a fixed number, or multiplying/dividing by a constant factor.
- Composite operations
- Some patterns combine two operations, such as "sum of first two numbers minus a constant equals the third," or "product of two numbers divided by a factor gives the third."
- Symmetric patterns
- Matrices may exhibit symmetry — elements in symmetric positions (e.g., top-left and bottom-right) may be related by a fixed rule.
- Prime, square, or factorial sequences
- Occasionally the pattern involves recognizing a mathematical sequence (squares: 1, 4, 9, 16; primes: 2, 3, 5, 7) rather than a simple arithmetic operation.
- Letter sequences
- For pure alphabetical matrices, check for forward/backward progressions, skipping letters, or cyclic patterns (e.g., every third letter).
Embedded Figures — Logical Reasoning · 8 cards
- Simple Figure
- The target shape you must find—typically a geometric form like a triangle, square, circle, arrow, or letter. This figure is always shown clearly and separately.
- Complex Figure
- A busy diagram containing many overlapping lines, shapes, and patterns. The simple figure is hidden somewhere within this visual clutter, maintaining its exact shape and proportions.
- Exact Match Required
- The embedded figure must have the same shape, angles, and proportions as the simple figure. A similar but not identical shape is incorrect. Rotations are generally not allowed unless specified.
- No Overlapping Rule
- In most SOF NSO questions, the embedded figure's outline should not share lines with other shapes—it should be traceable as a distinct, complete figure within the complex diagram.
- Systematic Scanning
- Successful solvers mentally divide the complex figure into zones (top-left, top-right, center, etc.) and check each systematically rather than looking randomly.
- Edge and Corner Strategy
- The embedded figure often appears at edges or corners of the complex figure, or sometimes right in the center. These locations should be checked first.
- Mental Tracing
- Train yourself to mentally trace the outline of the simple figure within the complex one. If you can complete the trace without interruption, you've found it.
- Distractor Elements
- Complex figures deliberately include shapes that almost match the simple figure but differ in one angle, side length, or curve. These are distractors designed to trap hasty students.
Mirror and Water Images — Logical Reasoning · 7 cards
- Mirror Image (Lateral Inversion)
- Reflection along a vertical axis—left becomes right and right becomes left, but top remains top and bottom remains bottom. Imagine holding a word up to a mirror placed vertically in front of you.
- Water Image (Vertical Inversion)
- Reflection along a horizontal axis—top becomes bottom and bottom becomes top, but left remains left and right remains right. Picture a word reflected in still water below it.
- Axis of Reflection
- The invisible line along which the flip occurs. For mirror images the axis is vertical (between object and mirror); for water images it's horizontal (between object and water surface).
- Symmetric vs Asymmetric Elements
- Letters like A, H, I, M, O, T, U, V, W, X, Y look identical or nearly identical after mirror reflection. Letters like B, C, D, E, F, G, J, K, L, N, P, Q, R, S, Z change significantly.
- Combined Transformations
- Some problems show a mirror image of a water image (or vice versa), which equals a 180° rotation. Recognizing this shortcut saves time.
- Figure Features
- For complex figures, track orientation of arrows, positions of dots, direction of curves, and relative positions of components—all must flip correctly according to the reflection axis.
- No Rotation
- Mirror and water images are pure reflections, not rotations. The object doesn't turn—it flips across an axis. Confusing reflection with rotation is the most common conceptual error.
Paper Folding and Cutting — Logical Reasoning · 6 cards
- Folding creates layers
- Each fold doubles the number of paper layers at that location. One fold = 2 layers, two folds = 4 layers (if folded in the same region), and so on.
- Cuts replicate across layers
- A single cut through folded paper creates identical holes in every layer beneath. If you cut through 4 layers, you create 4 identical holes in corresponding positions.
- Symmetry is your compass
- Folds create axes of symmetry. A vertical fold produces left-right symmetry; a horizontal fold produces top-bottom symmetry. Diagonal folds create diagonal symmetry axes.
- Unfold in reverse order
- To predict the final pattern, mentally unfold the paper in the exact reverse sequence of how it was folded. Each unfold step mirrors the cut pattern across the fold line.
- Corner folds are special
- Folding corners (triangular folds) creates radial or rotational patterns rather than simple mirror patterns. The cut position relative to the corner determines the final design.
- Number of holes = number of layers
- If you make one cut through N layers that does not touch any fold line, you'll see N holes when fully unfolded; copies cut across a fold join into one hole. The spatial arrangement follows the symmetry of the folds.
Cubes and Dice — Logical Reasoning · 7 cards
- Standard dice configuration
- A normal die has opposite faces summing to 7 (1–6, 2–5, 3–4). This rule helps identify opposite faces when two or three views are given.
- Painted cube formula
- When a large cube of side n units is painted and cut into unit cubes, specific formulas count cubes by number of painted faces—essential for rapid calculation without drawing.
- Adjacent vs opposite faces
- Two faces sharing an edge are adjacent; two faces never visible together in any view are opposite. Tracking adjacency helps reconstruct the entire cube from partial views.
- Rotation and reflection
- A cube shown in different orientations is still the same cube. Learn to mentally rotate cubes clockwise/counterclockwise to match given configurations.
- Counting cubes in stacks
- For 3D assemblies built from unit cubes, count visible cubes from one view, then add hidden cubes by analyzing the structure layer-by-layer.
- Open vs closed dice
- Open dice problems show a flat net (unfolded cube)—you fold it mentally to identify which faces meet. Closed dice show the assembled cube from multiple angles.
- Corner, edge, and face cubes
- In painted cube problems, cubes at corners have 3 painted faces, edge cubes have 2, face-center cubes have 1, and internal cubes have 0.
Motion — Science · 8 cards
- Distance vs Displacement
- Distance is the total path length traveled (scalar, always positive). Displacement is the shortest straight-line distance from start to finish with direction (vector, can be zero or negative).
- Speed vs Velocity
- Speed is distance/time (scalar). Velocity is displacement/time (vector). Average velocity can be zero even if average speed is not, if the object returns to its starting point.
- Acceleration
- Rate of change of velocity. Positive acceleration means speeding up in the positive direction or slowing down in the negative direction. Negative acceleration (retardation) means slowing down in the positive direction.
- Uniform Motion
- Object covers equal distances in equal intervals of time — velocity is constant, acceleration is zero.
- Non-Uniform Motion
- Velocity changes with time — acceleration is non-zero. The three kinematic equations apply only when acceleration is constant.
- Scalar vs Vector
- Distance and speed are scalars (magnitude only). Displacement, velocity, and acceleration are vectors (magnitude and direction).
- Instantaneous vs Average
- Instantaneous velocity is velocity at a specific instant. Average velocity is total displacement divided by total time. For uniform acceleration, average velocity = (initial + final velocity)/2.
- Graphical Representation
- Distance-time graph slope gives speed. Velocity-time graph slope gives acceleration, and the area under the curve gives displacement.
Force and Laws of Motion — Science · 8 cards
- Force
- is a push or pull that changes or tends to change the state of rest or uniform motion of an object. SI unit: Newton (N). 1 N = 1 kg·m/s².
- Inertia
- is the tendency of an object to resist changes in its state of motion. Mass is the measure of inertia—heavier objects have more inertia.
- Newton's First Law (Law of Inertia)
- An object at rest stays at rest, and an object in uniform motion stays in uniform motion, unless acted upon by an external unbalanced force.
- Newton's Second Law
- The rate of change of momentum is directly proportional to the applied force and occurs in the direction of the force. Mathematically: F = ma (when mass is constant).
- Newton's Third Law
- For every action, there is an equal and opposite reaction. Forces always occur in pairs acting on different objects.
- Momentum (p)
- is the product of mass and velocity: p = mv. SI unit: kg·m/s. Momentum is a vector quantity.
- Law of Conservation of Momentum
- In an isolated system with no external forces, the total momentum before an event equals the total momentum after the event. Critical for collision and explosion problems.
- Balanced forces
- produce no change in motion (zero net force). Unbalanced forces cause acceleration.
Gravitation — Science · 6 cards
- Universal Law of Gravitation
- Every object in the universe attracts every other object with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. This explains planetary orbits, tides, and why objects fall to Earth.
- Gravitational Constant (G)
- The value 6.67 × 10⁻¹¹ N m²/kg² is a universal constant. It remains the same everywhere in the universe, unlike acceleration due to gravity (g) which varies with location.
- Free Fall
- Motion of an object under the sole influence of gravity (ignoring air resistance). All objects, regardless of mass, fall with the same acceleration g = 9.8 m/s² near Earth's surface.
- Mass vs Weight
- Mass is the amount of matter in an object (scalar, measured in kg, constant everywhere). Weight is the gravitational force on an object (vector, measured in newtons, varies with location).
- Acceleration due to Gravity (g)
- On Earth's surface g ≈ 9.8 m/s² or 10 m/s² (for quick calculations). It decreases with altitude and differs on other planets/moons based on their mass and radius.
- Thrust and Pressure
- Thrust is the perpendicular force acting on a surface. Pressure is thrust per unit area. Fluids (liquids and gases) exert pressure in all directions; pressure increases with depth in a liquid column.
Work and Energy — Science · 6 cards
- Work
- is done when a force causes displacement in its direction. If force and displacement are perpendicular (like centripetal force in circular motion), work done is zero. Work is a scalar quantity measured in joules.
- Kinetic Energy (KE)
- is the energy possessed by a body due to its motion. It depends on mass and the square of velocity, so doubling velocity quadruples kinetic energy. A moving bullet, flowing river, and spinning wheel all have kinetic energy.
- Potential Energy (PE)
- is the energy stored in a body due to its position or configuration. Gravitational PE increases with height above ground; elastic PE stores when you compress a spring or stretch a rubber band.
- Conservation of Energy
- states that energy can neither be created nor destroyed, only transformed from one form to another. The total mechanical energy (KE + PE) of a system remains constant in the absence of friction or air resistance.
- Power
- measures the rate of doing work or the rate of energy transfer. A more powerful engine does the same work in less time. Power determines how quickly energy is converted from one form to another.
- Energy transformations
- occur continuously—chemical energy in food converts to kinetic energy when you run, electrical energy becomes light and heat in a bulb, and potential energy of water at a height becomes kinetic energy in turbines.
Sound — Science · 8 cards
- Sound is a mechanical wave
- It requires a material medium (solid, liquid or gas) to travel. Sound cannot propagate through vacuum because there are no particles to vibrate.
- Production by vibration
- All sound originates from vibrating objects. When an object vibrates, it creates compressions (high pressure regions) and rarefactions (low pressure regions) in the surrounding medium, forming a longitudinal wave.
- Speed varies with medium
- Sound travels fastest in solids (particles are closely packed), slower in liquids, and slowest in gases. In air at 20°C, speed ≈ 344 m/s; in water ≈ 1500 m/s; in steel ≈ 5000 m/s. Speed increases with temperature in gases.
- Pitch depends on frequency
- High frequency sounds have high pitch (like a whistle), low frequency sounds have low pitch (like a drum). Human hearing range: 20 Hz to 20,000 Hz. Sounds below 20 Hz are infrasonic; above 20,000 Hz are ultrasonic.
- Loudness depends on amplitude
- Greater amplitude means more energy and louder sound. Loudness is measured in decibels (dB). Normal conversation ≈ 60 dB; threshold of pain ≈ 120 dB.
- Quality (timbre) distinguishes sources
- Even at the same pitch and loudness, a flute and violin sound different due to quality, which depends on the waveform and presence of overtones (harmonics).
- Echo is reflected sound
- When sound reflects off a hard surface and returns to the listener with a time gap, it's heard as an echo. Minimum distance needed: 17 m (for 0.1 s distinction time in air).
- Reverberation vs echo
- Reverberation is prolonged reflection causing persistence of sound in enclosed spaces. Unlike distinct echoes, reverberations blend together creating a continuous effect.
Electricity (Class 10) — Science · 8 cards
- Electric Current
- Flow of electric charge through a conductor, measured in amperes (A). Direction of conventional current is opposite to electron flow. 1 ampere = 1 coulomb per second (1 A = 1 C/s).
- Electric Potential and Potential Difference
- Work done per unit charge to move charge between two points. Measured in volts (V). 1 volt = 1 joule per coulomb (1 V = 1 J/C). Potential difference drives current flow.
- Resistance
- Opposition to current flow in a conductor, measured in ohms (Ω). Depends on length (directly proportional), cross-sectional area (inversely proportional), temperature, and material (resistivity ρ).
- Ohm's Law
- At constant temperature, current through a conductor is directly proportional to potential difference across it: V = IR. This relationship holds for ohmic conductors (metals) but not for devices like diodes or transistors.
- Series Circuit
- Components connected end-to-end in a single path. Same current flows through all components. Total voltage divides across components. Total resistance equals sum of individual resistances.
- Parallel Circuit
- Components connected across common points with multiple current paths. Same voltage across all components. Total current divides among branches. Reciprocal of total resistance equals sum of reciprocals of individual resistances.
- Electric Power
- Rate of electrical energy consumption, measured in watts (W). Power consumed depends on both voltage and current. 1 watt = 1 joule per second. Household appliances are rated in watts or kilowatts.
- Electric Energy
- Total electrical work done or energy consumed over time, measured in joules (J) or kilowatt-hours (kWh). 1 kWh = 3.6 × 10⁶ J. Electricity bills are calculated based on energy consumption in kWh units.
Magnetic Effects of Current (Class 10) — Science · 8 cards
- Magnetic Field of a Straight Conductor
- A current-carrying straight wire produces concentric circular magnetic field lines around it. Direction given by right-hand thumb rule: thumb along current, fingers curl in field direction.
- Magnetic Field of a Circular Loop
- At the center of a circular loop, field lines are nearly straight. Field strength increases with current and decreases with loop radius. One face acts as north pole, the other as south.
- Solenoid
- A long coil of many circular turns. When current flows, it behaves like a bar magnet with a north pole at one end and south pole at the other. Field inside is uniform and strong; outside is weak and similar to a bar magnet.
- Electromagnetic Induction
- Faraday discovered that changing magnetic flux through a coil induces an EMF (voltage). This requires relative motion between magnet and coil, or changing current in a nearby coil.
- Fleming's Right-Hand Rule (Generator)
- Thumb = motion of conductor, First finger = magnetic field direction, Middle finger = induced current direction. Used to find current direction in generators.
- AC vs DC Generator
- AC generator uses slip rings (continuous rotating contact) producing alternating current that reverses direction every half rotation. DC generator uses a split-ring commutator that reverses connection every half rotation, producing unidirectional current.
- Electric Motor
- Converts electrical energy to mechanical energy. Current in a coil within a magnetic field experiences force (Fleming's left-hand rule), causing rotation. Split-ring commutator reverses current every half turn to maintain continuous rotation.
- Transformer
- Changes AC voltage using two coils (primary and secondary) wound on an iron core. Mutual induction between coils allows voltage step-up or step-down. Does not work with DC because constant current produces no flux change.
Light — Reflection and Refraction (Class 10) — Science · 8 cards
- Laws of Reflection
- The incident ray, reflected ray, and normal all lie in the same plane. The angle of incidence equals the angle of reflection (∠i = ∠r).
- Spherical Mirrors
- Concave mirrors converge light (can form real or virtual images), while convex mirrors diverge light (always form virtual, diminished, erect images). The principal focus of a concave mirror is real; for a convex mirror, it is virtual.
- Refraction
- When light travels from one transparent medium to another, it changes speed and bends at the boundary. Light bends toward the normal when entering a denser medium and away when entering a rarer medium.
- Refractive Index
- The refractive index n of a medium is the ratio of the speed of light in vacuum to the speed of light in that medium. n = c/v. Higher refractive index means light travels slower in that medium.
- Snell's Law
- At the interface of two media, n₁ sin i = n₂ sin r, where n₁ and n₂ are refractive indices and i, r are angles of incidence and refraction.
- Total Internal Reflection
- When light travels from denser to rarer medium and the angle of incidence exceeds the critical angle, light reflects entirely back into the denser medium. This principle underlies optical fibers and phenomena like mirages.
- Lenses
- Convex lenses converge light (real focus, can form real or virtual images), while concave lenses diverge light (virtual focus, always form virtual, diminished, erect images). Lens behavior depends on the curvature and refractive index.
- Power of Lens
- Power P = 1/f (in meters). Measured in diopters (D). Positive for convex lenses, negative for concave lenses. Power is additive for lenses in contact: P_total = P₁ + P₂.