JEE · Physics doubts
172 doubts found
What does “Least count” actually mean in Units, Dimensions & Measurement, and why does it matter for JEE?
the smallest value an instrument can reliably read — e.g. 0.01 mm for a screw gauge.
What does “Projectile motion” actually mean in Kinematics, and why does it matter for JEE?
motion under gravity where horizontal and vertical motions are independent — horizontal a=0, vertical a=−g.
What does “Friction” actually mean in Laws of Motion, and why does it matter for JEE?
static friction adjusts itself up to a maximum μₛN to prevent motion; kinetic friction μₖN opposes sliding.
What does “Power” actually mean in Work, Energy & Power, and why does it matter for JEE?
the rate of doing work, P = W/t = F·v.
What does “Angular momentum” actually mean in Rotational Motion, and why does it matter for JEE?
L = Iω, conserved when the net external torque is zero.
What does “Escape velocity” actually mean in Gravitation, and why does it matter for JEE?
the minimum speed to leave a planet's gravity, v = √(2GM/R) ≈ 11.2 km/s for Earth.
What does “Kinetic theory of gases” actually mean in Thermodynamics & Kinetic Theory, and why does it matter for JEE?
gas pressure comes from molecular collisions, and average molecular KE is proportional to absolute temperature.
What does “Beats” actually mean in Oscillations & Waves, and why does it matter for JEE?
the slow throbbing when two close frequencies superpose; beat frequency = |f₁ − f₂|.
What does “Capacitance” actually mean in Electrostatics, and why does it matter for JEE?
a capacitor's ability to store charge per volt, C = Q/V; for parallel plates C = ε₀A/d.
What does “EMF and terminal voltage” actually mean in Current Electricity, and why does it matter for JEE?
EMF is the battery's full push; terminal voltage is what's left after the internal resistance drops some of it.
What does “Magnetic flux” actually mean in Magnetism & Electromagnetic Induction, and why does it matter for JEE?
Φ = B·A·cosθ — the amount of field passing through a loop.
What does “Mass–energy and binding energy” actually mean in Modern Physics, and why does it matter for JEE?
a nucleus weighs less than its parts; the missing mass becomes binding energy via E = Δmc².
I keep getting “Least count” questions wrong in Units, Dimensions & Measurement. What's the trap?
forgetting the zero-error correction of a vernier or screw gauge.
I keep getting “Projectile motion” questions wrong in Kinematics. What's the trap?
applying v=u+at to the whole velocity instead of resolving into x and y components.
I keep getting “Friction” questions wrong in Laws of Motion. What's the trap?
assuming friction always equals μN — static friction is only as big as needed, up to its limit.
I keep getting “Power” questions wrong in Work, Energy & Power. What's the trap?
confusing power (how fast work is done) with energy (the total work).
I keep getting “Angular momentum” questions wrong in Rotational Motion. What's the trap?
forgetting that pulling mass inward lowers I and therefore speeds up rotation.
I keep getting “Escape velocity” questions wrong in Gravitation. What's the trap?
confusing it with orbital velocity.
I keep getting “Kinetic theory of gases” questions wrong in Thermodynamics & Kinetic Theory. What's the trap?
using Celsius instead of Kelvin in gas relations.
I keep getting “Beats” questions wrong in Oscillations & Waves. What's the trap?
adding the frequencies instead of subtracting.
I keep getting “Capacitance” questions wrong in Electrostatics. What's the trap?
forgetting a dielectric increases capacitance.
I keep getting “EMF and terminal voltage” questions wrong in Current Electricity. What's the trap?
assuming terminal voltage equals EMF even when current flows.
I keep getting “Magnetic flux” questions wrong in Magnetism & Electromagnetic Induction. What's the trap?
ignoring the angle between the field and the loop's normal.
I keep getting “Mass–energy and binding energy” questions wrong in Modern Physics. What's the trap?
ignoring the mass defect when computing nuclear energy.