Work, Energy, Heat & Thermodynamics

A step-up transformer has more turns in the secondary coil than the primary. From Vs/Vp = Ns/Np, more secondary turns → higher output voltage. Used at power stations for efficient long-distance transmission.

Trap: 'Equal to input' baits those who confuse step-up with isolating transformers.

Appeared MPT 2024 — Repeated twice

A microphone converts mechanical sound waves into electrical audio signals via electromagnetic induction or piezoelectric principles. The output is the audio signal.

Trap: 'Sound wave' is the input, not the electrical output.

Appeared MPT 2024 — Repeated twice

Due to anomalous expansion, water reaches maximum density at 4°C. Below 4°C, water expands on cooling (less dense), which is why ice floats.

Trap: 0°C (freezing point) is the intuitive but wrong reflex.

Appeared MPT 2024

Steam at 100°C carries the additional latent heat of vaporisation (~2,260 kJ/kg). When it condenses on skin, this hidden energy is released, causing more severe burns than liquid at the same temperature.

Trap: 'Has higher temperature' is the surface-level misread — both are at 100°C.

Appeared MPT 2023 — Latent heat trap

Transformers require a CHANGING magnetic flux to induce voltage. DC produces constant current → constant flux → no induction → zero output.

Trap: Option D (one direction) is partially true but not the root cause — the issue is unchanging flux.

FPSC Elite Trap — Induction requires CHANGING flux

In physics (light), primary colors are Red, Green, Blue (RGB). Mixing all three produces white light. RYB is the art/pigment model — not relevant to physics.

Trap: Red, Yellow, Blue (the art convention) is the planted bait for physics questions.

Appeared MPT 2023 — Physics RGB, not art RYB

Convex mirrors produce a virtual, upright, diminished image with a wide field of view — letting drivers see a large area behind them. Concave mirrors magnify (used in shaving mirrors).

Trap: 'Concave mirror' is the swapped-shape trap.

Appeared MPT 2022 and 2025

Hyperopia means the image focuses behind the retina. A convex (converging) lens bends light to bring the focal point onto the retina. Concave lens is for myopia.

Trap: 'Concave lens' baits those who confuse the two corrective lens types.

Appeared MPT 2025

All three are confirmed 2024 past paper facts: step-up transformer increases voltage; transformer needs changing flux (AC only); microphone output is an audio electrical signal.

Trap: Partial-correct options (A, B, C) bait those who doubt one of the three.

FPSC Elite Trap — All three confirmed 2024 past paper facts

KE = ½mv². When v doubles → (2v)² = 4v² → kinetic energy increases by a factor of 4. This is why crashes at 80 km/h are 4× more destructive than at 40 km/h.

Trap: 'Double' is the linear-reflex trap — it ignores that v is squared.

FPSC Elite Trap — KE = ½mv² — velocity is squared

Statement 1 ✓: conduction works through direct molecular contact in solids. Statement 2 ✓: convection moves heat via fluids. Statement 3 ✗: radiation is electromagnetic — it travels through vacuum (no medium required). Sunlight reaches Earth this way.

Trap: Statement 3 is the planted error — feels intuitive that 'all heat needs a medium.'

FPSC Elite Trap — Statement 3 FALSE: radiation travels through vacuum

During a phase change, all supplied energy goes into breaking molecular bonds (latent heat of fusion). The temperature stays constant at 0°C until the entire ice has melted; only afterward does temperature begin to rise.

Trap: 'Increases gradually' is the intuitive but wrong assumption — heating during phase change does not raise temperature.

FPSC Elite Trap — Latent heat keeps temperature constant during phase change