JEE · Physics doubts
172 doubts found
What does “Significant figures” actually mean in Units, Dimensions & Measurement, and why does it matter for JEE?
the digits in a measurement that actually carry meaning, reflecting the instrument's precision.
What does “Acceleration” actually mean in Kinematics, and why does it matter for JEE?
the rate of change of velocity; it is a vector, so direction matters.
What does “Newton's second law” actually mean in Laws of Motion, and why does it matter for JEE?
the net force equals mass times acceleration, F=ma, in the direction of the net force.
What does “Work–energy theorem” actually mean in Work, Energy & Power, and why does it matter for JEE?
the net work done on a body equals its change in kinetic energy.
What does “Torque” actually mean in Rotational Motion, and why does it matter for JEE?
the turning effect of a force, τ = r×F = rF·sinθ — the rotational analogue of force.
What does “Acceleration due to gravity g” actually mean in Gravitation, and why does it matter for JEE?
g = GM/R² at a planet's surface; it decreases with both altitude and depth.
What does “Internal energy” actually mean in Thermodynamics & Kinetic Theory, and why does it matter for JEE?
the total microscopic energy of a system; for an ideal gas it depends only on temperature.
What does “Time period of a pendulum” actually mean in Oscillations & Waves, and why does it matter for JEE?
T = 2π√(L/g) — it depends on length and gravity, not on mass or (small) amplitude.
What does “Electric field” actually mean in Electrostatics, and why does it matter for JEE?
the force per unit positive charge, E = F/q; field lines point away from positive charges.
What does “Resistance and resistivity” actually mean in Current Electricity, and why does it matter for JEE?
R = ρL/A: resistance grows with length and shrinks with cross-section; resistivity ρ is the material's own property.
What does “Faraday's law of induction” actually mean in Magnetism & Electromagnetic Induction, and why does it matter for JEE?
a changing magnetic flux induces an EMF, EMF = −dΦ/dt.
What does “Photon energy” actually mean in Modern Physics, and why does it matter for JEE?
light comes in packets of energy E = hf = hc/λ.
I keep getting “Significant figures” questions wrong in Units, Dimensions & Measurement. What's the trap?
keeping more digits in the answer than the least-precise measurement allows.
I keep getting “Acceleration” questions wrong in Kinematics. What's the trap?
assuming acceleration is zero whenever velocity is zero (e.g. at the top of a throw, v=0 but a=−g).
I keep getting “Newton's second law” questions wrong in Laws of Motion. What's the trap?
using a single force instead of the net (vector sum) force.
I keep getting “Work–energy theorem” questions wrong in Work, Energy & Power. What's the trap?
using only one force's work instead of the net work.
I keep getting “Torque” questions wrong in Rotational Motion. What's the trap?
using the force alone instead of force times perpendicular (lever-arm) distance.
I keep getting “Acceleration due to gravity g” questions wrong in Gravitation. What's the trap?
treating g as a fixed 9.8 everywhere, including in orbit.
I keep getting “Internal energy” questions wrong in Thermodynamics & Kinetic Theory. What's the trap?
thinking internal energy depends on pressure or volume for an ideal gas.
I keep getting “Time period of a pendulum” questions wrong in Oscillations & Waves. What's the trap?
thinking a heavier bob swings with a different period.
I keep getting “Electric field” questions wrong in Electrostatics. What's the trap?
treating field (a vector) and potential (a scalar) as the same thing.
I keep getting “Resistance and resistivity” questions wrong in Current Electricity. What's the trap?
confusing resistance (depends on shape) with resistivity (depends only on material and temperature).
I keep getting “Faraday's law of induction” questions wrong in Magnetism & Electromagnetic Induction. What's the trap?
expecting a steady (unchanging) magnetic field to induce an EMF.
I keep getting “Photon energy” questions wrong in Modern Physics. What's the trap?
treating light purely as a wave when explaining the photoelectric effect.