JEE · Physics doubts
235 doubts found
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.
Why is a dam built much thicker at the bottom than at the top?
Water pressure grows with depth, P = ρgh, so the deepest water pushes hardest on the wall.
Why is the daytime sky blue but the Sun turns red at sunset?
Air molecules scatter shorter (blue) wavelengths far more than longer (red) ones — Rayleigh scattering, which goes as 1/λ⁴.
I keep getting “Coherence” questions wrong in Wave Optics. What's the trap?
expecting two ordinary bulbs to interfere.
I keep getting “Reactance” questions wrong in Alternating Current. What's the trap?
treating reactance as a fixed resistance.
I keep getting “Depletion region” questions wrong in Semiconductor Electronics (Diodes). What's the trap?
thinking the depletion region has free charge carriers.
What does “Relative velocity in two dimensions” actually mean in Motion in a Plane, and why does it matter for JEE?
The velocity of A as seen from B is v_A/B = v_A - v_B. This subtraction explains rain direction, river crossings and moving-platform questions.
What does “Phase change and latent heat” actually mean in Thermal Properties of Matter, and why does it matter for JEE?
During an ideal phase change at fixed pressure, supplied heat rearranges particles instead of raising temperature, so temperature stays constant until the change finishes.
What does “Degrees of freedom” actually mean in Kinetic Theory of Gases, and why does it matter for JEE?
A degree of freedom is an independent quadratic way a molecule can store energy. Translational, rotational and vibrational modes contribute depending on molecular structure and temperature.