Physics Paper 3 June 2003

1. AAny object moving along a curved path must be losing speed continuously, which is what defines acceleration.
2. BAcceleration only occurs when speed changes, so a body moving at constant speed can never be accelerating.
3. CThe body accelerates only at the instant it starts moving, and travels at constant velocity for the rest of the circular path once it reaches full speed.
4. DAcceleration is the rate of change of velocity; a constant change of direction changes the velocity even though the speed stays the same.

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1. AAt the bottom of the circle, because the string tension is greatest there, needing to supply both the centripetal force and support the weight.
2. BAt the side of the circle, because the string is horizontal there and must carry the full weight of the bob without any vertical help from its own tension.
3. CThe tension is the same everywhere in the circle, so the string is equally likely to break at any point.
4. DAt the top of the circle, because the string tension is smallest there.

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1. AF = GM_eM/r^2 (gravitational force) and F = Mrω^2 (centripetal force), with ω = 2π/T.
2. BPV = nRT, applied to the gas inside the satellite's cabin.
3. CF = ma and v = u + at, applied to the satellite's straight-line motion along a fixed radial direction toward the planet's centre.
4. DE = mc^2 and p = mv, applied to the satellite's total energy.

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1. ABecause the induced current always flows in the same direction as the change that produces it, releasing stored energy for free without any work being done.
2. BBecause Lenz's law only applies when no current is actually induced, so no energy is ever transferred.
3. CBecause the induced e.m.f. is always exactly zero once the system reaches a steady, unchanging state.
4. DBecause work must be done against the opposing force set up by the induced current, and it is this work that supplies the electrical energy generated.

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1. AThe wire's own resistance decreases as it moves faster, allowing more current to flow at higher speed.
2. BMoving the wire changes its temperature, and the resulting thermoelectric effect is what drives the current.
3. CThe area swept by the wire changes with time, changing the magnetic flux through the circuit and so inducing an e.m.f. that drives a current in the closed circuit.
4. DThe magnetic field itself is switched on and off rapidly as the wire moves, which is what induces the current in this kind of moving-wire circuit, rather than any change in swept area.

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1. AIt must vary with pressure but stay completely constant with temperature.
2. BIt must be capable of being calibrated at known fixed points, so readings can be extrapolated to other temperatures.
3. CIt must only change value at exactly 0 degC and remain fixed at every other temperature, never varying continuously across the working range.
4. DIt must be visible to the naked eye without any form of scale or calibration.

1. AA sealed glass bulb of coloured liquid that expands up a capillary tube as its temperature rises.
2. BTwo dissimilar metal wires joined at a hot and a cold junction, producing a thermoelectric e.m.f. that depends on the temperature difference between the junctions.
3. CA bimetallic strip that bends by an amount proportional to the temperature change.
4. DA single metal wire whose resistance is measured directly with an ohmmeter as it changes with temperature, requiring no reference junction or second dissimilar wire at all.

1. AIt responds instantly to rapidly changing temperatures, unlike the thermocouple.
2. BIt never requires calibration at any fixed points before use.
3. CIt can only be used at temperatures below 0 degC, unlike a thermocouple.
4. DIt measures constant or slowly-changing temperatures more accurately.

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1. ATheir thermometric properties do not vary with temperature in exactly the same way, except at the fixed calibration points themselves.
2. BOne of the two thermometers must be broken, since correctly calibrated thermometers always agree exactly at every temperature between the fixed points.
3. CThe bath temperature itself changes depending on which thermometer is inserted into it.
4. DResistance thermometers cannot be calibrated at fixed points at all, unlike thermocouples.

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1. AThis can never happen; any increase in a substance's total energy must always raise its temperature.
2. BWhenever the substance is heated slowly enough, regardless of whether it changes phase.
3. CDuring a change of phase, when the extra (latent heat) energy goes into breaking or forming bonds between atoms rather than raising their kinetic energy.
4. DOnly when the substance is compressed to a much smaller volume without any heat being supplied at all, which is treated here as the sole possible exception to the rule.

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1. AThe drop's terminal (falling) velocity is measured, then the field is adjusted to hold the drop stationary; the charge is deduced from the field needed to balance its weight.
2. BThe drop's charge is read directly from a meter connected to the microscope used to view it.
3. CThe drop's colour under illumination is compared against a reference chart to read off its charge directly.
4. DThe drop is weighed on a sensitive balance both before and after being sprayed through the apparatus, and the charge is deduced from the small change in mass measured this way.

1. AEvery measured charge on a drop is found to be an integer multiple of a single basic charge, about 1.6x10^-19 C.
2. BThe measured charge on different drops varies completely continuously, taking any value whatsoever with no smallest unit.
3. CAll oil drops in the experiment are found to carry exactly the same charge, regardless of how many electrons they have gained or lost.
4. DThe charge measured depends only on the size of the drop, not on any underlying fundamental unit of charge.

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1. AIt travels straight through undeviated, since glass is transparent to visible light.
2. BIt undergoes total internal reflection, since 54.7 degrees exceeds the glass's critical angle of 42 degrees.
3. CIt refracts out into the air at exactly 54.7 degrees, since this is less than 90 degrees and so is assumed to always permit refraction regardless of the critical angle.
4. DIt is completely absorbed by the glass at this face, since the angle exceeds 45 degrees.

1. AIn a progressive wave, particles between two adjacent nodes are always in phase; in a stationary wave, neighbouring particles are instead always out of phase with each other.
2. BPhase differences between particles only exist in stationary waves, never in progressive waves.
3. CIn both wave types, every particle in the medium vibrates exactly in phase with every other particle at all times.
4. DIn a progressive wave, neighbouring particles are generally out of phase with each other; in a stationary wave, particles between the same two nodes vibrate in phase.

1. AIn a stationary wave every particle has the same, constant amplitude, identical regardless of its position between two nodes.
2. BAmplitude is undefined for a stationary wave, since its particles do not actually move at all.
3. CIn a progressive wave every particle has the same amplitude; in a stationary wave the amplitude varies from zero at the nodes to a maximum at the antinodes.
4. DIn a progressive wave the amplitude varies between different particles along the wave; in a stationary wave every particle instead shares one fixed, non-zero amplitude throughout.

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1. AA planet is a satellite of a moon; a star orbits a planet; galaxies make up a star; the universe is made of galaxies.
2. BMoons, planets and stars are all identical objects that simply differ in the name astronomers happen to give them.
3. CA galaxy is a satellite of a star, and the universe is a single very large galaxy containing every star.
4. DA moon is a satellite of a planet; a planet orbits a star; stars make up a galaxy; galaxies make up the universe.

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1. AIt shows the universe has always existed in a fixed, unchanging steady state with no beginning.
2. BIt is emitted only by nearby stars in our own galaxy and has no connection to the universe's origin.
3. CIt proves the universe is contracting rather than expanding, since its cosmic background temperature is observed by astronomers to be steadily rising over time.
4. DIt supports the Big Bang theory: as the universe expanded and cooled, this background radiation cooled with it, indicating a finite age for the universe.

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1. AA steady direct voltage of 3.0 V, since the sinusoidal signal V2 is fully filtered out by the op-amp before it can reach the output stage.
2. BA clean sine wave with the same peak voltage as V2, but shifted up by exactly 3.0 V.
3. CA square wave alternating between +15 V and -15 V, switching each time V2 crosses the 3.0 V reference level.
4. DA steady direct voltage of 4.5 V, since V2's peak simply overrides V1.

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1. AThe object's speed, its shape and cross-sectional area, and the fluid's viscosity and density.
2. BOnly the fluid's temperature, which is assumed to fully determine the drag on any object regardless of its speed, shape or the fluid's density.
3. COnly the object's colour and the ambient temperature of the surrounding air.
4. DOnly the object's mass, regardless of its shape, speed or the fluid's properties.

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1. AThe pupil widens for near objects and narrows for distant ones, which alone is assumed here to be what changes the eye's focus without any change in the lens itself.
2. BThe cornea's curvature reverses direction depending on whether the object is near or far.
3. CThe ciliary muscles contract to thicken the lens for near objects, and relax to thin the lens for distant objects, changing its focal length.
4. DThe eyeball itself physically changes length, moving the retina closer to or further from the lens.

1. AAn eyeball that is too long (too great a distance between lens and retina), or ciliary muscles that do not relax well enough to thin the lens fully.
2. BAn eyeball that is too short for its lens, or ciliary muscles that are permanently paralysed and cannot contract at all under any circumstance whatsoever.
3. CA cornea that is completely flat, or a retina that is more sensitive to light than normal.
4. DA lens with too little curvature at all times, regardless of the ciliary muscles' state.

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1. AA system that automatically removes the moderator from the reactor whenever a power failure occurs.
2. BA mechanical fail-safe system that automatically pushes the control rods into the reactor core to shut it down if power is lost.
3. CA system that automatically increases the coolant temperature to slow the chain reaction during a power failure, without needing the control rods.
4. DThere is no way to prevent this: any power failure inevitably makes a chain reaction uncontrollable.

1. AThe formula itself is dimensionally inconsistent, so it never gives a physically meaningful value in the first place for any real turbine.
2. BReal air has zero density, so the density term in the formula does not actually apply to a genuine wind turbine.
3. CThe air passing through the blades cannot be reduced to zero velocity afterwards, so some kinetic energy always remains in the outflow.
4. DWind turbine blades are always stationary in practice, so no power at all can ever be extracted from the wind.

1. AThey pass straight through the Earth itself to reach the far side directly.
2. BThey are repeatedly reflected between the Earth's surface and the ionosphere, allowing them to travel beyond the horizon.
3. CThey travel in a perfectly straight line and simply have a very long range that always exceeds the horizon regardless of transmitter power.
4. DThey are reflected only once, directly off the Moon, before reaching the receiver.

1. AAM uses no carrier wave at all, while FM combines two separate carrier waves at different frequencies.
2. BIn AM the carrier's amplitude varies with the audio signal while its frequency stays constant; in FM the carrier's frequency varies with the audio signal while its amplitude stays constant.
3. CIn AM the carrier's frequency varies with the audio signal; in FM the carrier's amplitude varies with the audio signal, with the opposite quantity held fixed in each case rather than the frequency.
4. DAM and FM both vary the carrier's amplitude and frequency together, in exact proportion to each other.

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