For Class 8, 9 & 10
Master the basics - and everything after gets easier
Concept-first questions with clear model answers in Physics, Chemistry, Maths and Biology, all NCERT-aligned. Start early, build the habit, and walk into your boards, NEET and JEE already ahead.
Interactive lessons
learn by playingDrag, slide and build - watch each concept come alive, then reveal the answer.
200 interactive lessons
Ohm's law
Class 10 Physics
Slide V & R, watch the bulb glow
Open →pH scale
Class 10 Chemistry
Slide across acids and bases
Open →Atomic number and mass number
Class 9 Chemistry
Add protons & neutrons, build shells
Open →Laws of reflection
Class 8 Physics
Change the angle, watch it bounce
Open →Volume of a sphere
Class 9 Maths
Grow the radius, see the volume
Open →Area of a trapezium
Class 8 Maths
Drag the sides, read the area
Open →Power of a lens
Class 10 Physics
Move the object, trace the rays
Open →Food chain and energy flow
Class 10 Biology
Follow the energy as it flows
Open →Speed
Class 8 Physics
Slide distance & time, watch the speed
Open →Density
Class 9 Physics
Pack mass into volume, float or sink
Open →Work done
Class 9 Physics
Push harder or farther, watch work grow
Open →Kinetic energy
Class 9 Physics
Speed it up - energy grows with the square
Open →Power of a lens
Class 10 Physics
Shorten the focal length, boost the power
Open →Mole concept
Class 9 Chemistry
Weigh out grams, count the moles
Open →Avogadro's number
Class 9 Chemistry
Add moles, count the particles
Open →Microscope magnification
Class 8 Biology
Grow the image, read the magnification
Open →Population density
Class 10 Biology
Add individuals, shrink the land, see crowding
Open →Simple interest
Class 8 Maths
Slide money, rate & time, watch interest
Open →Pythagoras theorem
Class 9 Maths
Stretch the two sides, get the hypotenuse
Open →Probability of an event
Class 10 Maths
Change the outcomes, watch the odds
Open →Newton's second law
Class 9 Physics
Push a mass, pick an acceleration
Open →Momentum
Class 9 Physics
Slide mass & velocity, build momentum
Open →Pressure
Class 8 Physics
Shrink the area, feel the pressure rise
Open →Weight
Class 9 Physics
Change the planet's gravity, watch your weight
Open →Refractive index
Class 10 Physics
Slow light in the medium, raise the index
Open →Resistors in series
Class 10 Physics
Add two resistors in a line
Open →Mass percentage of a solution
Class 9 Chemistry
Dissolve solute, read the strength
Open →Concentration of a solution
Class 9 Chemistry
Pack solute into less liquid
Open →Population change
Class 10 Biology
Balance births against deaths
Open →Compound microscope
Class 8 Biology
Combine eyepiece & objective lenses
Open →Area of a circle
Class 8 Maths
Grow the radius, watch the area square
Open →Volume of a cuboid
Class 8 Maths
Stretch length, breadth & height
Open →Electronic configuration and valency
Class 9 Chemistry
Slide the atomic number, build the atom
Open →Homologous series (alkanes)
Class 10 Chemistry
Add carbons, name the compound
Open →Mass number
Class 9 Chemistry
Add protons & neutrons, get the mass number
Open →Power
Class 9 Physics
More work in less time = more power
Open →Potential energy
Class 9 Physics
Lift a mass higher, store energy
Open →Wave speed
Class 9 Physics
Tune frequency & wavelength, set the speed
Open →Electric current
Class 10 Physics
Push charge per second, get the current
Open →Percentage
Class 8 Maths
Compare part to whole as a %
Open →Electron dot structure
Class 9 Chemistry
Draw valence electrons as dots
Open →Acceleration
Class 9 Physics
Speed up over time, find acceleration
Open →Distance, speed and time
Class 8 Physics
Set speed & time, cover the distance
Open →Frequency and time period
Class 9 Physics
Shorten the period, raise the frequency
Open →Heating effect of current
Class 10 Physics
Raise the current, watch heating soar
Open →Area of a triangle
Class 8 Maths
Set base & height, halve the rectangle
Open →Area of a rectangle
Class 8 Maths
Set length & breadth, fill the area
Open →Mean (average)
Class 9 Maths
Share the total equally across items
Open →Discount
Class 8 Maths
Slide price & % off, see the saving
Open →Heart rate
Class 10 Biology
Set heart rate & time, count the beats
Open →Resistors in parallel
Class 10 Physics
Wire two resistors side by side
Open →Electric charge
Class 10 Physics
Flow current over time, collect charge
Open →Electrical energy and units
Class 10 Physics
Run appliances, add up the units
Open →Kelvin temperature scale
Class 9 Chemistry
Slide Celsius, read the Kelvin
Open →Moles from number of particles
Class 9 Chemistry
Divide particles by Avogadro's number
Open →Ten percent law
Class 10 Biology
See 10% of energy reach the next level
Open →Area of a square
Class 8 Maths
Grow the side, square the area
Open →Volume of a cube
Class 8 Maths
Grow the edge, cube the volume
Open →Circumference of a circle
Class 8 Maths
Grow the radius, roll out the rim
Open →Surface area of a cube
Class 9 Maths
Grow the edge, cover six faces
Open →Potential difference
Class 10 Physics
Share work across charge, get volts
Open →Resistance from Ohm's law
Class 10 Physics
Divide voltage by current, get resistance
Open →Echo and SONAR
Class 9 Physics
Time the echo, find the distance
Open →Mass from moles
Class 9 Chemistry
Multiply moles by molar mass
Open →Breathing rate
Class 10 Biology
Set breathing rate & time
Open →Volume of a cylinder
Class 10 Maths
Set radius & height, fill the can
Open →Compound interest
Class 8 Maths
Compound money over years
Open →Profit and loss percentage
Class 8 Maths
Set cost & selling price, see profit %
Open →Perimeter of a rectangle
Class 8 Maths
Set length & breadth, walk the border
Open →Surface area of a sphere
Class 10 Maths
Grow the radius, wrap the ball
Open →Time period
Class 9 Physics
Raise the frequency, shrink the period
Open →Relative velocity
Class 9 Physics
Two objects approach - add their speeds
Open →Average velocity
Class 9 Physics
Average the start and end speeds
Open →Equations of motion (v = u + at)
Class 9 Physics
Accelerate from u for a time t
Open →Kelvin to Celsius
Class 9 Chemistry
Slide Kelvin, read the Celsius
Open →Population growth rate
Class 10 Biology
Balance births vs deaths per population
Open →Perimeter of a square
Class 8 Maths
Grow the side, walk four edges
Open →Perimeter of a triangle
Class 8 Maths
Add the three sides
Open →Area of a parallelogram
Class 8 Maths
Set base & height, slide the shape
Open →Area of a rhombus
Class 8 Maths
Set the two diagonals
Open →Equations of motion (distance)
Class 9 Physics
Start, accelerate, cover ground
Open →Joule's law of heating
Class 10 Physics
Raise current, resistance or time
Open →Electric power (P = VI)
Class 10 Physics
Multiply voltage by current
Open →Average atomic mass of isotopes
Class 9 Chemistry
Mix two isotopes by abundance
Open →Seed germination percentage
Class 9 Biology
Count sprouted seeds out of the total
Open →Volume of a cone
Class 9 Maths
Set radius & height, fill the cone
Open →Surface area of a cylinder
Class 9 Maths
Wrap the side and both ends
Open →Surface area of a cuboid
Class 9 Maths
Cover all six rectangular faces
Open →nth term of an AP
Class 10 Maths
Step from the first term by d
Open →Sum of an AP
Class 10 Maths
Add up the first n terms
Open →Focal length of a mirror
Class 10 Physics
Halve the radius to find the focus
Open →Speed of light in a medium
Class 10 Physics
Raise the index, slow the light
Open →Percentage purity
Class 9 Chemistry
Weigh the pure part of a sample
Open →Slope of a line
Class 10 Maths
Rise over run gives the steepness
Open →Percentage change
Class 8 Maths
Compare a new value to the old
Open →Volume of a hemisphere
Class 9 Maths
Grow the radius of half a ball
Open →Area of a sector
Class 10 Maths
Cut a slice of angle from a circle
Open →Length of an arc
Class 10 Maths
Measure the curved edge of a slice
Open →Slant height of a cone
Class 9 Maths
Combine radius & height for the slant
Open →Unit conversion (km/h to m/s)
Class 9 Physics
Convert km/h into m/s
Open →Equations of motion (v^2 = u^2 + 2as)
Class 9 Physics
Accelerate over a distance, find v
Open →Impulse
Class 9 Physics
Hit harder or longer, change momentum
Open →Wavelength
Class 9 Physics
Speed over frequency gives wavelength
Open →Oscillations
Class 9 Physics
Vibrate at a frequency for a time
Open →Cost of electricity
Class 10 Physics
Units times rate gives the bill
Open →Number of neutrons
Class 9 Chemistry
Take protons away from the mass number
Open →Curved surface area of a cone
Class 9 Maths
Wrap the slanted side of a cone
Open →Total surface area of a cone
Class 9 Maths
Add the base circle to the cone's side
Open →Curved surface area of a hemisphere
Class 9 Maths
Cover the dome of a hemisphere
Open →Diagonal of a square
Class 9 Maths
Cross a square corner to corner
Open →Unit conversion (m/s to km/h)
Class 9 Physics
Convert m/s into km/h
Open →Distance from velocities
Class 9 Physics
From two speeds, find the distance
Open →Diagonal of a rectangle
Class 9 Maths
Cross a rectangle corner to corner
Open →Diagonal of a cuboid
Class 9 Maths
The longest rod that fits in a box
Open →Area by Heron's formula
Class 9 Maths
Area from just the three sides
Open →Interior angle sum of a polygon
Class 8 Maths
Add up a polygon's inside angles
Open →Exterior angle of a regular polygon
Class 8 Maths
Share 360 among a polygon's corners
Open →Number of diagonals of a polygon
Class 8 Maths
Count the diagonals of a polygon
Open →Discriminant
Class 10 Maths
Test how many roots a quadratic has
Open →Sum of roots
Class 10 Maths
Sum of a quadratic's roots
Open →Punnett square (monohybrid cross)
Class 10 Biology
Cross two parents, predict the offspring
Open →Balancing chemical equations
Class 10 Chemistry
Slide coefficients until atoms balance
Open →Writing chemical formulae (valency)
Class 9 Chemistry
Criss-cross valencies into a formula
Open →Current from power
Class 10 Physics
Divide power by voltage for current
Open →Power (P = V^2 / R)
Class 10 Physics
Voltage squared over resistance
Open →Sine ratio
Class 10 Maths
Opposite over hypotenuse
Open →Cosine ratio
Class 10 Maths
Adjacent over hypotenuse
Open →Tangent ratio
Class 10 Maths
Opposite over adjacent
Open →Area of an equilateral triangle
Class 9 Maths
Area of an equilateral triangle
Open →Curved surface area of a cylinder
Class 9 Maths
Wrap only the curved side
Open →Loss percentage
Class 8 Maths
Sell below cost, find the loss %
Open →Amount with simple interest
Class 8 Maths
Principal plus its simple interest
Open →Distance formula
Class 10 Maths
Straight distance between two points
Open →States of matter
Class 9 Chemistry
Heat particles solid → liquid → gas
Open →Parts of a plant cell
Class 8 Biology
Tap a cell part to see its job
Open →Diagonal of a cube
Class 9 Maths
Longest diagonal through a cube
Open →Total surface area of a hemisphere
Class 9 Maths
Dome plus its flat circle
Open →Sum of first n natural numbers
Class 10 Maths
Add 1 + 2 + ... + n instantly
Open →Range of data
Class 9 Maths
Spread from smallest to largest
Open →Class mark
Class 9 Maths
Midpoint of a class interval
Open →Selling price from profit percent
Class 8 Maths
Mark up cost by a profit %
Open →Perimeter of a sector
Class 10 Maths
Two radii plus the curved arc
Open →Circumference from diameter
Class 8 Maths
Circumference straight from diameter
Open →Power (P = F x v)
Class 9 Physics
Force times velocity gives power
Open →Percentage of a number
Class 8 Maths
Find a percentage of a number
Open →Series and parallel circuits
Class 10 Physics
Break a bulb in series vs parallel
Open →Symbols of elements
Class 9 Chemistry
Match each element to its symbol
Open →Free fall (velocity)
Class 9 Physics
Drop from a height, hit this speed
Open →Free fall (time)
Class 9 Physics
How long a drop takes
Open →Free fall (distance)
Class 9 Physics
Distance fallen in a given time
Open →Complement of an event
Class 10 Maths
Chance an event does NOT happen
Open →Product of roots
Class 10 Maths
Product of a quadratic's roots
Open →Exterior angle theorem
Class 9 Maths
Exterior angle = sum of remote interiors
Open →Complementary angles
Class 10 Maths
What adds to 90 degrees
Open →Supplementary angles
Class 9 Maths
What adds to 180 degrees
Open →Perimeter of a semicircle
Class 10 Maths
Curved half plus the diameter
Open →Area of a semicircle
Class 10 Maths
Half the area of a circle
Open →Turning effect (moments)
Class 9 Physics
Balance the see-saw with moments
Open →Reflex arc
Class 10 Biology
Step through a reflex, stimulus to action
Open →Buoyant force (upthrust)
Class 9 Physics
Displace liquid, feel the upthrust
Open →Relative density
Class 9 Physics
Compare a density to water's
Open →Power in lifting a load
Class 9 Physics
Lift a load, faster needs more power
Open →Cosecant ratio
Class 10 Maths
Hypotenuse over opposite
Open →Secant ratio
Class 10 Maths
Hypotenuse over adjacent
Open →Cotangent ratio
Class 10 Maths
Adjacent over opposite
Open →Height from angle of elevation
Class 10 Maths
Height from an angle of elevation
Open →Area of a quadrant
Class 10 Maths
A quarter of a circle's area
Open →Interior angle of a regular polygon
Class 8 Maths
One inside angle of a regular polygon
Open →Sum of first n odd numbers
Class 10 Maths
Add the first n odd numbers
Open →Sum of first n even numbers
Class 10 Maths
Add the first n even numbers
Open →Quadratic formula (a root)
Class 10 Maths
Larger root of a quadratic
Open →LCM from HCF
Class 10 Maths
LCM from the product and HCF
Open →Depreciation
Class 8 Maths
Value drops by a % each year
Open →Cost price from selling price
Class 8 Maths
Work back to the cost price
Open →Downstream speed
Class 8 Maths
Row with the current
Open →Upstream speed
Class 8 Maths
Row against the current
Open →Average speed for a round trip
Class 8 Maths
Average speed there and back
Open →Sales tax / GST
Class 8 Maths
Tax added on a price
Open →Area of a ring (annulus)
Class 10 Maths
Area of a ring between two circles
Open →Edge of a cube from volume
Class 9 Maths
Edge back from the volume
Open →Radius from area
Class 10 Maths
Radius back from a circle's area
Open →Side from area of a square
Class 8 Maths
Side back from a square's area
Open →Height of a triangle from area
Class 9 Maths
Height back from area and base
Open →Rate from simple interest
Class 8 Maths
Rate back from the interest
Open →Time from simple interest
Class 8 Maths
Time back from the interest
Open →Principal from simple interest
Class 8 Maths
Principal back from the interest
Open →Mean proportional
Class 10 Maths
Geometric mean of two numbers
Open →Fourth proportional
Class 8 Maths
Complete the proportion a : b = c : ?
Open →Marked price from selling price
Class 8 Maths
Marked price back from the sale price
Open →Chambers of the human heart
Class 10 Biology
Tap a heart chamber to see its job
Open →Equation of a line (y = mx + c)
Class 9 Maths
Read y off a straight line
Open →Average term of an AP
Class 10 Maths
Average of first and last term
Open →Number of terms in an AP
Class 10 Maths
How many terms in an AP
Open →Midpoint of two points
Class 10 Maths
x-coordinate of a midpoint
Open →Empirical mode
Class 10 Maths
Estimate the mode from mean & median
Open →Length of a shadow
Class 10 Maths
Shadow from height and sun angle
Open →Train crossing a pole
Class 8 Maths
Speed to cross a pole
Open →Time and work
Class 8 Maths
More workers, fewer days
Open →Dividing in a ratio
Class 8 Maths
Split a total in a ratio
Open →Unitary method
Class 8 Maths
Cost of a single item
Open →Your progress — Foundation - Class 8 to 10
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Showing 8 questions for Class 10. Tap a card to reveal the answer.
PhysicsThe Human Eye and the Colourful WorldmediumWhy does the clear sky appear blue?
Reveal answer ↓
What it is
The sky is blue because tiny air molecules scatter blue light much more than red.
Answer
Sunlight is scattered by the tiny molecules of air in the atmosphere. Blue light has a shorter wavelength and is scattered much more strongly than red light. As this scattered blue light reaches our eyes from all directions, the clear sky appears blue. At sunset the light travels a longer path, most of the blue is scattered away, and the remaining red light makes the sky look reddish.
- •Air molecules scatter sunlight
- •Blue (shorter wavelength) scatters most
- •Scattered blue reaches our eyes -> blue sky
- •Sunset: blue scattered away, red remains
Why learn this
The same scattering explains red sunsets and why danger signals are red (least scattered).
💡 Memory trick
Blue scatters most (short wavelength), so the sky looks blue; at sunset the long red light survives.
PhysicsThe Human Eye and the Colourful WorldmediumWhy does the clear sky appear blue?
Reveal answer ↓
What it is
Air molecules scatter shorter (blue) wavelengths much more than red, so the clear sky looks blue.
Answer
As sunlight passes through the atmosphere it is scattered by the tiny molecules of air. Scattering is much stronger for shorter wavelengths, so blue light is scattered far more than red light. This scattered blue light reaches our eyes from every part of the sky, making a clear sky look blue. Near sunrise and sunset the light travels a much longer path through the air, most of the blue is scattered away, and the Sun appears red.
Scattering is stronger for shorter wavelengths
- •Air molecules scatter sunlight
- •Shorter wavelength (blue) scatters more
- •Scattered blue reaches the eye from all directions
- •Long path at sunset removes blue, so the Sun looks red
Why learn this
The same idea explains red sunrises and sunsets - physics you can watch every day.
💡 Memory trick
Blue is scattered most (short wavelength). At sunset light travels far, blue is lost, so the Sun looks red.
PhysicsThe Human Eye and the Colourful WorldmediumName the main parts of the human eye and their functions.
Reveal answer ↓
What it is
The eye focuses light using the cornea and lens to form a real, inverted image on the retina.
Answer
The main parts of the human eye are: the cornea, the transparent front part where most refraction occurs; the iris, which controls the size of the pupil; the pupil, the opening that lets light in; the eye lens, which fine-tunes the focus; the retina, the light-sensitive screen where a real, inverted image forms; and the optic nerve, which carries signals to the brain. The ciliary muscles change the shape of the lens.
- •Cornea: main refraction, front
- •Iris and pupil: control light entering
- •Lens: fine focusing
- •Retina: real inverted image; optic nerve to brain
Why learn this
It explains how we see and where each part fits in.
💡 Memory trick
Cornea + lens focus light -> retina catches the image -> optic nerve sends it to the brain.
PhysicsThe Human Eye and the Colourful WorldmediumWhat is the power of accommodation of the eye?
Reveal answer ↓
What it is
Accommodation is the ability of the eye lens to change its focal length to focus objects at different distances.
Answer
The power of accommodation is the ability of the eye lens to adjust its focal length so that objects at different distances can be focused sharply on the retina. When we look at a distant object, the ciliary muscles relax, the lens becomes thin and its focal length increases. When we look at a nearby object, the ciliary muscles contract, the lens becomes thick and its focal length decreases. However, the lens cannot become thinner or thicker beyond a limit, so there is a nearest point (about 25 cm) called the near point.
- •Lens changes focal length to focus
- •Ciliary muscles relax for distant objects
- •Ciliary muscles contract for near objects
- •Least distance of distinct vision is about 25 cm
Why learn this
It lets us see both nearby and distant objects clearly.
💡 Memory trick
Ciliary muscles squeeze the lens for near objects and relax for far objects.
PhysicsThe Human Eye and the Colourful WorldmediumWhat is myopia? State its cause and correction.
Reveal answer ↓
What it is
In myopia a person can see near objects clearly but not distant ones; it is corrected with a concave lens.
Answer
Myopia, or short-sightedness, is a defect of vision in which a person can see nearby objects clearly but cannot see distant objects distinctly. It is caused when the image of a distant object is formed in front of the retina, either because the eyeball is too long or the lens is too curved (its focal length is too short). It is corrected by using spectacles with a concave (diverging) lens of suitable power, which spreads the rays slightly so the image forms on the retina.
- •Near objects clear, distant blurred
- •Image forms in front of the retina
- •Caused by long eyeball or too-curved lens
- •Corrected with a concave lens
Why learn this
It is one of the most common vision defects, corrected by spectacles.
💡 Memory trick
Myopia = near vision OK, far blurry. Correct with a concave (diverging) lens.
PhysicsThe Human Eye and the Colourful WorldmediumWhat is hypermetropia and how is it corrected? What is presbyopia?
Reveal answer ↓
What it is
In hypermetropia distant objects are seen clearly but near ones are not; it is corrected with a convex lens.
Answer
Hypermetropia, or long-sightedness, is a defect in which a person can see distant objects clearly but cannot focus on nearby objects; the image of a near object forms behind the retina, because the eyeball is too short or the lens focal length is too long. It is corrected using a convex (converging) lens of suitable power. Presbyopia is a defect that comes with old age, in which the eye loses its power of accommodation because the ciliary muscles weaken and the lens becomes less flexible; it is often corrected with bifocal lenses.
- •Hypermetropia: distant clear, near blurred
- •Image forms behind the retina
- •Corrected with a convex lens
- •Presbyopia: age-related loss of accommodation (bifocals)
Why learn this
It is a common defect, especially with age (presbyopia).
💡 Memory trick
Hypermetropia = far vision OK, near blurry. Correct with a convex (converging) lens.
PhysicsThe Human Eye and the Colourful WorldmediumWhat is dispersion of light? Why does it occur?
Reveal answer ↓
What it is
A prism splits white light into its seven component colours because each colour bends by a different amount.
Answer
Dispersion of light is the splitting of white light into its seven constituent colours - violet, indigo, blue, green, yellow, orange and red (VIBGYOR) - when it passes through a prism. It occurs because light of different colours has different wavelengths and therefore bends (refracts) by different amounts in the prism; violet light bends the most and red light the least. The band of colours obtained is called a spectrum. A rainbow forms by dispersion of sunlight through raindrops.
- •White light splits into seven colours (VIBGYOR)
- •Different colours bend by different amounts
- •Violet bends most, red least
- •Rainbow is natural dispersion by raindrops
Why learn this
It explains the formation of a rainbow.
💡 Memory trick
VIBGYOR: Violet bends most, Red bends least. White light is a mix of seven colours.
PhysicsThe Human Eye and the Colourful WorldmediumWhy is the sky blue and the Sun reddish at sunrise and sunset?
Reveal answer ↓
What it is
Scattering of light by small particles explains the blue colour of the sky and the red colour of the Sun at sunrise and sunset.
Answer
The molecules of air and fine particles in the atmosphere scatter shorter wavelengths (blue) of sunlight much more strongly than longer wavelengths (red). During the day, this scattered blue light reaches our eyes from all directions, so the sky appears blue. At sunrise and sunset, sunlight travels a longer path through the atmosphere, so most of the blue light is scattered away and only the longer-wavelength red light reaches us, making the Sun appear reddish.
- •Small particles scatter blue light most
- •Scattered blue light makes the sky blue
- •At sunset light travels a longer path
- •Blue is scattered away, so the Sun looks red
Why learn this
It explains everyday sky colours and the Tyndall effect.
💡 Memory trick
Blue scatters most (short wavelength) -> blue sky. At sunset, light travels far, blue is scattered away, so we see red.
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