JEE doubts
500 doubts found
What does “Dimensional analysis” actually mean in Units, Dimensions & Measurement, and why does it matter for JEE?
expressing every quantity in powers of mass (M), length (L) and time (T) so you can check or derive relations.
What does “Instantaneous velocity” actually mean in Kinematics, and why does it matter for JEE?
the velocity at a single instant — the slope of the position–time graph at that point.
What does “Inertia” actually mean in Laws of Motion, and why does it matter for JEE?
the tendency of a body to resist any change in its state of rest or uniform motion (Newton's first law).
What does “Work” actually mean in Work, Energy & Power, and why does it matter for JEE?
energy transferred by a force: W = F·d·cosθ, where θ is the angle between force and displacement.
What does “Centre of mass” actually mean in Rotational Motion, and why does it matter for JEE?
the single point where the whole mass of a system can be treated as concentrated.
What does “Universal law of gravitation” actually mean in Gravitation, and why does it matter for JEE?
every two masses attract with F = G·m₁m₂/r² along the line joining them.
What does “First law of thermodynamics” actually mean in Thermodynamics & Kinetic Theory, and why does it matter for JEE?
energy conservation for gases: ΔU = Q − W, where W is work done BY the gas.
What does “Simple harmonic motion” actually mean in Oscillations & Waves, and why does it matter for JEE?
oscillation where the restoring force is proportional to and opposite the displacement, F = −kx.
What does “Coulomb's law” actually mean in Electrostatics, and why does it matter for JEE?
the force between two point charges, F = kq₁q₂/r², along the line joining them.
What does “Ohm's law” actually mean in Current Electricity, and why does it matter for JEE?
for many conductors V = IR at constant temperature.
What does “Magnetic force on a moving charge” actually mean in Magnetism & Electromagnetic Induction, and why does it matter for JEE?
F = qvB·sinθ, always perpendicular to the velocity, so it changes direction but not speed.
What does “Photoelectric effect” actually mean in Modern Physics, and why does it matter for JEE?
light ejects electrons from a metal only if its frequency exceeds a threshold, regardless of intensity.
I keep getting “Dimensional analysis” questions wrong in Units, Dimensions & Measurement. What's the trap?
thinking a dimensionally-correct equation must be numerically correct — dimensionless constants (like 2 or π) are invisible to it.
I keep getting “Instantaneous velocity” questions wrong in Kinematics. What's the trap?
confusing average velocity (total displacement/total time) with instantaneous velocity.
I keep getting “Inertia” questions wrong in Laws of Motion. What's the trap?
thinking a moving body needs a continuous force to keep moving — it doesn't, unless friction acts.
I keep getting “Work” questions wrong in Work, Energy & Power. What's the trap?
forgetting the cosθ — a force perpendicular to the motion does zero work.
I keep getting “Centre of mass” questions wrong in Rotational Motion. What's the trap?
assuming it always lies inside the body (for a ring it's at the empty centre).
I keep getting “Universal law of gravitation” questions wrong in Gravitation. What's the trap?
forgetting the force depends on 1/r² — doubling the distance quarters the force.
I keep getting “First law of thermodynamics” questions wrong in Thermodynamics & Kinetic Theory. What's the trap?
getting the sign of W wrong (work done by vs on the gas).
I keep getting “Simple harmonic motion” questions wrong in Oscillations & Waves. What's the trap?
assuming every back-and-forth motion is SHM.
I keep getting “Coulomb's law” questions wrong in Electrostatics. What's the trap?
ignoring that like charges repel and unlike attract when assigning direction.
I keep getting “Ohm's law” questions wrong in Current Electricity. What's the trap?
assuming every component is ohmic (a diode or bulb filament is not).
I keep getting “Magnetic force on a moving charge” questions wrong in Magnetism & Electromagnetic Induction. What's the trap?
thinking the magnetic force can speed a charge up.
I keep getting “Photoelectric effect” questions wrong in Modern Physics. What's the trap?
thinking very bright low-frequency light can eject electrons.