Physics

Exam focus: Dimensional analysis can check an equation's consistency or derive how variables combine, but it can never fix a pure numerical constant like the ½ in KE = ½mv², and it can't distinguish between quantities that share dimensions, such as work and torque.

3 topics · 3 lectures · 18 questions · 3 with exam focus

Exam focus: Area under a v-t graph gives displacement, not distance — where the graph dips below the axis that area subtracts, so total distance needs the positive and negative areas summed separately, not net.

3 topics · 3 lectures · 11 questions · 3 with exam focus

Exam focus: The resultant of two vectors is maximum (A+B) when they're parallel and minimum (|A−B|) when antiparallel — it's never zero unless the two magnitudes are equal, a quick check for ruling out impossible resultants.

3 topics · 3 lectures · 7 questions · 3 with exam focus

Exam focus: Action–reaction pairs act on two different bodies, so they can never be added together to argue that nothing accelerates — a body stays at rest only when the net force on that one body is zero.

4 topics · 4 lectures · 11 questions · 4 with exam focus

Exam focus: Work is zero whenever force stays perpendicular to displacement at every instant — centripetal force on a circling body and the upward force on someone carrying a bag horizontally both do zero work.

4 topics · 4 lectures · 12 questions · 4 with exam focus

Exam focus: Internal forces — an explosion, an internal collision — never change the centre of mass's velocity or path, only external forces do; a shell that explodes mid-air has its COM land exactly where the intact shell would have.

4 topics · 4 lectures · 16 questions · 4 with exam focus

Exam focus: g falls off in both directions from the surface but not symmetrically: it drops as g(1−2h/R) with altitude, roughly twice as fast per unit distance as g(1−d/R) with depth, and reaches zero only at the centre.

3 topics · 3 lectures · 12 questions · 3 with exam focus

Exam focus: Hooke's law (stress ∝ strain) holds only up to the proportional limit — the elastic limit lies slightly beyond it, so a material can still spring back to shape over a small range where stress and strain aren't proportional.

3 topics · 3 lectures · 6 questions · 3 with exam focus

Exam focus: Buoyant force depends only on the volume of fluid displaced and the fluid's density — once an object is fully submerged, pushing it deeper doesn't change the buoyant force, since the displaced volume stays the same.

4 topics · 4 lectures · 10 questions · 4 with exam focus

Exam focus: For an isotropic solid the linear, areal and volume expansion coefficients are in the ratio 1:2:3, so 'the' expansion coefficient without saying which one invites a factor-of-2-or-3 error; water alone contracts while warming from 0°C to 4°C.

4 topics · 4 lectures · 6 questions · 4 with exam focus

Exam focus: Internal energy is a state function — for an ideal gas it depends on temperature alone — while heat and work are path-dependent, so two different processes between the same states can have very different Q and W despite identical ΔU.

3 topics · 3 lectures · 6 questions · 3 with exam focus

Exam focus: At a fixed temperature, rms speed depends only on molar mass — lighter molecules move faster, not slower, which is why hydrogen effuses faster than oxygen at the same temperature.

3 topics · 3 lectures · 10 questions · 3 with exam focus

Exam focus: Total energy in SHM is constant and proportional to amplitude squared, but keeps trading between KE (maximum at the mean position) and PE (maximum at the extremes) — and acceleration itself is never constant, since a = −ω²x.

3 topics · 3 lectures · 12 questions · 3 with exam focus

Exam focus: Wave speed is fixed by the medium's own properties, not by the source's frequency or the wave's amplitude — crossing into a new medium leaves frequency exactly as the source set it, while wavelength and speed both change.

3 topics · 3 lectures · 4 questions · 3 with exam focus

Exam focus: Force from multiple charges adds as vectors, not scalars — the net force on a charge comes from superposing each pairwise Coulomb force with its own direction, so just adding magnitudes fails whenever the charges aren't collinear.

3 topics · 3 lectures · 9 questions · 3 with exam focus

Exam focus: Potential from multiple charges adds as plain signed numbers, not vectors, much simpler than combining fields — and a dipole's potential is exactly zero at every point on its equatorial line, not just far away.

3 topics · 3 lectures · 19 questions · 3 with exam focus

Exam focus: Resistivity is a property of the material only — stretching a wire to twice its length doubles R (since R = ρl/A) but leaves ρ itself unchanged, and resistivity rises with temperature for metals but falls for semiconductors.

3 topics · 3 lectures · 26 questions · 3 with exam focus

Exam focus: The magnetic force on a moving charge is always perpendicular to its velocity, so it can never change the charge's speed or kinetic energy, only its direction — and it's exactly zero when velocity is parallel or antiparallel to B.

3 topics · 3 lectures · 16 questions · 3 with exam focus

Exam focus: Magnetic field lines always form closed loops with no start or end point, since isolated magnetic poles don't exist — unlike electric field lines, which begin and end on charges. A bar magnet's field falls off as 1/r³, its axial value twice the equatorial one.

3 topics · 3 lectures · 6 questions · 3 with exam focus

Exam focus: Lenz's law says the induced effect opposes the change in flux, not the flux itself — if flux through a loop is decreasing, the induced current flows to try to maintain it, not to fight its existing direction.

3 topics · 3 lectures · 9 questions · 3 with exam focus

Exam focus: In a pure inductor, current lags voltage by 90°; in a pure capacitor, it leads by 90° — remembered as 'ELI the ICE man' (in L, voltage E leads current I; in C, current I leads voltage E).

3 topics · 3 lectures · 14 questions · 3 with exam focus

Exam focus: Displacement current isn't an actual flow of charge — it's the term Maxwell added so Ampère's law gives a consistent answer for any surface, and the textbook example is a charging capacitor's gap, where conduction current is zero but displacement current isn't.

2 topics · 2 lectures · 12 questions · 2 with exam focus

Exam focus: The biggest source of errors here is sign convention: a concave mirror has negative f, a convex mirror positive f — a convex mirror's image is always virtual and upright regardless of object distance, and getting the sign backwards flips every later answer.

3 topics · 3 lectures · 19 questions · 3 with exam focus

Exam focus: Huygens' wave theory correctly predicted that light slows down in a denser medium, v = c/n — the opposite of Newton's corpuscular prediction — a difference that later measurement of light's speed in water settled in the wave theory's favour.

3 topics · 3 lectures · 9 questions · 3 with exam focus

Exam focus: Increasing light intensity increases the number of photoelectrons, not their maximum kinetic energy — that depends only on frequency, KEmax = hν − φ — and below the threshold frequency, no electrons come out no matter how bright the light is.

2 topics · 2 lectures · 16 questions · 2 with exam focus

Exam focus: Rutherford's model correctly located the nucleus but couldn't explain atomic stability — classically an accelerating orbiting electron should radiate energy and spiral inward. Bohr fixed exactly this by allowing only orbits with quantised angular momentum, L = nh/2π.

2 topics · 2 lectures · 8 questions · 2 with exam focus

Exam focus: Binding energy per nucleon peaks near mass number 56 (iron) and falls on both sides — exactly why fusion of light nuclei and fission of heavy nuclei both release energy, moving toward that peak. Nuclear density comes out roughly the same for every nucleus.

3 topics · 3 lectures · 10 questions · 3 with exam focus

Exam focus: Doping never leaves a semiconductor charged — an n-type material has extra free electrons as majority carriers, but the donor ion left behind balances the charge exactly, so the material as a whole stays electrically neutral.

3 topics · 3 lectures · 20 questions · 3 with exam focus