JEE · Physics doubts
172 doubts found
How is Units, Dimensions & Measurement tested in JEE, and what should I focus on?
Prioritise the core ideas: Dimensional analysis, Significant figures, Errors in measurement.
What is the difference between average velocity and instantaneous velocity?
Average velocity is displacement over a time interval; instantaneous velocity is the value at one exact moment.
What is the difference between inertial frame and non-inertial frame?
An inertial frame moves at constant velocity (Newton's laws hold directly); a non-inertial frame accelerates (you must add pseudo-forces).
When do I use KE = ½mv² in Work, Energy & Power, and what does it mean?
kinetic energy of a moving body.
What is the difference between rolling and sliding?
A rolling body has both translational and rotational KE and (with friction) doesn't slip; a sliding body has only translational KE.
What is the difference between weight and gravitational force?
Weight is the gravitational force experienced (mg); in free fall the sensation of weight vanishes even though gravity still acts.
When do I use PV = nRT in Thermodynamics & Kinetic Theory, and what does it mean?
ideal-gas equation of state.
When do I use T = 2π√(L/g) in Oscillations & Waves, and what does it mean?
period of a simple pendulum.
When do I use E = kQ/r² in Electrostatics, and what does it mean?
field of a point charge at distance r.
When do I use R = ρL/A in Current Electricity, and what does it mean?
resistance from resistivity, length and area.
When do I use F = BIL sinθ in Magnetism & Electromagnetic Induction, and what does it mean?
force on a current-carrying wire in a field.
What is the difference between intrinsic semiconductor and extrinsic semiconductor?
Intrinsic is pure silicon/germanium; extrinsic is deliberately doped to boost conductivity.
What are the most common mistakes students make in Units, Dimensions & Measurement?
round only at the final step, never in the middle of a calculation.
When do I use v = u + at in Kinematics, and what does it mean?
final velocity after time t under constant acceleration.
When do I use fₛ(max) = μₛN in Laws of Motion, and what does it mean?
the maximum static friction before an object starts to slip.
When do I use P = Fv in Work, Energy & Power, and what does it mean?
instantaneous power from force and velocity.
When do I use τ = Iα in Rotational Motion, and what does it mean?
rotational Newton's second law (torque = moment of inertia × angular acceleration).
When do I use F = G m₁m₂/r² in Gravitation, and what does it mean?
the gravitational force between two masses.
When do I use C_p − C_v = R in Thermodynamics & Kinetic Theory, and what does it mean?
Mayer's relation between molar heat capacities.
When do I use v = fλ in Oscillations & Waves, and what does it mean?
wave speed equals frequency times wavelength.
When do I use V = kQ/r in Electrostatics, and what does it mean?
potential of a point charge.
When do I use P = VI = I²R = V²/R in Current Electricity, and what does it mean?
electrical power dissipated.
When do I use EMF = −dΦ/dt in Magnetism & Electromagnetic Induction, and what does it mean?
Faraday's law of electromagnetic induction.
When do I use E = hf = hc/λ in Modern Physics, and what does it mean?
energy of a photon.