AQA GCSE Combined Science: Trilogy · 6.8

Key ideas - physics

Revision questions with answers for 6.8 Key ideas - physics in AQA GCSE Combined Science: Trilogy (spec 8464). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below.

All questions and answers

Question 1 · Links 6.3.1.1
Why is a particle model useful for explaining a material's state?
Answer:
Particle arrangement and motion provide a mechanism for its shape, volume and ability to flow.
Question 2 · Links 6.3.3.1
How does the particle model explain pressure increasing in a heated sealed rigid container?
Answer:
Faster particles collide with walls more frequently and with greater force, increasing pressure at fixed volume.
Question 3 · Links 6.6.1.1
What evidence distinguishes wave movement from bulk material movement?
Answer:
A point or particle oscillates locally while the disturbance and energy travel through the medium.
Question 4 · Links 6.6.2.2 · Higher only
Why can a wavefront model explain bending at a boundary?
Answer:
One part of the wavefront changes speed before another, rotating the front and changing the propagation direction.
Question 5 · Links 6.4.1.3
Why was alpha scattering more important than simply preferring a new atomic picture?
Answer:
Its observations contradicted a spread-out positive charge and supported a small dense nucleus, providing testable evidence for change.
Question 6 · Links 6.4.1.2
Why does changing neutron number affect isotope identity but not element identity?
Answer:
Element identity depends on proton number; neutron number changes the isotope and mass number.
Question 7 · Links 6.3.2.3
How does a heating-curve plateau reveal a limitation of temperature alone?
Answer:
Energy continues to enter during a state change even though temperature stays constant, so temperature does not measure total internal energy.
Question 8 · Links 6.6.1.2
Why are wave diagrams models rather than literal pictures of travelling matter?
Answer:
They represent quantities such as displacement and wavelength; they do not imply particles travel along the drawn curve.
Question 9 · Links 6.5.4.2.2
How does resultant force provide a cause for acceleration?
Answer:
A non-zero resultant force changes velocity according to F = ma; greater force produces greater acceleration at fixed mass.
Question 10 · Links 6.5.4.1.5
Why does increasing air resistance eventually stop a falling object's acceleration?
Answer:
Drag grows until it balances weight, making resultant force zero and velocity constant.
Question 11 · Links 6.2.1.4
How can heating a filament cause a curved I-V graph?
Answer:
As temperature rises, resistance increases, so current no longer rises in direct proportion to potential difference.
Question 12 · Links 6.4.2.2
Why does alpha emission change the element but gamma emission does not?
Answer:
Alpha emission changes proton number; gamma emission changes nuclear energy without changing proton number.
Question 13 · Links 6.4.1.1
How is an electron energy-level change linked to radiation?
Answer:
Absorption can raise an electron to a higher level; a fall to a lower level emits electromagnetic radiation.
Question 14 · Links 6.7.2.2 · Higher only
How can changing current reverse a mechanical effect?
Answer:
In a fixed magnetic field, reversing current reverses the motor-effect force and can reverse the resulting motion.
Question 15 · Links 6.5.4.3.4
How do energy and force explain the danger of stopping very quickly?
Answer:
A moving body's kinetic energy must be transferred; a short stopping distance or time produces a large decelerating force.
Question 16 · Links 6.1.2.1
Why must an energy explanation name both the initial and final stores?
Answer:
It shows where transferred energy came from and went, making conservation and unwanted transfers clear.
Question 17 · Links 6.5.1.3
How can Earth pull on an object without touching it?
Answer:
Its gravitational field exerts a force on the object's mass.
Question 18 · Links 6.7.1.2
How does a compass demonstrate action at a distance?
Answer:
Its magnetic needle experiences a turning effect and aligns with a field even without touching the source.
Question 19 · Links 6.5.1.2
How are electrostatic and magnetic forces similar as field effects?
Answer:
Both can act across a gap; their fields describe where and in which direction a test object experiences force.
Question 20 · Links 6.7.1.2
Why is field direction defined using a test north pole?
Answer:
It gives a consistent direction convention for the otherwise invisible magnetic interaction at each point.
Question 21 · Links 6.7.2.1
How does a current-carrying solenoid link electricity and magnetism?
Answer:
Moving charge produces a magnetic field; arranging the wire in a coil combines fields into a strong solenoid field.
Question 22 · Links 6.5.1.3
Why can an object's weight change while its mass remains constant?
Answer:
Weight depends on local gravitational field strength, W = mg; mass does not depend on location.
Question 23 · Links 6.1.2.1
Why does energy transfer from a hotter object towards cooler surroundings?
Answer:
The temperature difference drives net energy transfer by heating until thermal equilibrium is approached.
Question 24 · Links 6.2.1.3
Why does a larger potential difference drive more current through a fixed resistor?
Answer:
V = IR: with resistance constant, a greater potential difference produces a greater current.
Question 25 · Links 6.2.3.2
Why can touching live while connected to earth drive current through a person?
Answer:
The live-earth potential difference transfers energy to charge moving through the body, creating a hazardous current.
Question 26 · Links 6.3.2.3
Why can energy leave a freezing substance while its temperature remains constant?
Answer:
Its particles' potential energy decreases as the structure changes, transferring energy without lowering average kinetic energy during freezing.
Question 27 · Links 6.2.2
Why does a parallel branch receive the full supply potential difference?
Answer:
Its ends connect to the same two supply points, so each branch spans the same electrical potential difference.
Question 28 · Links 6.5.1.3
What graph shape demonstrates weight is proportional to mass at fixed g?
Answer:
A straight line through the origin; its gradient is gravitational field strength.
Question 29 · Links 6.5.3
What evidence shows a spring has gone beyond proportional behaviour?
Answer:
The force-extension graph no longer follows a straight line through the origin.
Question 30 · Links 6.1.1.2
How can doubling a car's speed affect the energy that brakes must transfer?
Answer:
At fixed mass, kinetic energy becomes four times larger, so brakes must transfer four times the energy to stop it.
Question 31 · Links 6.5.4.2.2
What happens to acceleration if mass doubles at fixed resultant force?
Answer:
It halves, because a = F/m.
Question 32 · Links 6.2.1.3
How can an I-V graph distinguish a fixed resistor from a filament lamp?
Answer:
The fixed-temperature resistor gives a straight line through the origin; the heating filament gives a curved line.
Question 33 · Links 6.6.1.2
Why does halving wavelength double frequency at fixed wave speed?
Answer:
The product f x wavelength stays equal to speed, so frequency must double.
Question 34 · Links 6.7.2.2 · Higher only
What happens to motor-effect force if both B and I double at fixed perpendicular length?
Answer:
F = BIl makes force four times larger.
Question 35 · Links 6.1.1.3
How does doubling mass affect temperature rise for the same energy input and material?
Answer:
The rise halves, from E = mc x temperature change.
Question 36 · Links 6.4.2.3 · Higher only
Why is radioactive decay not a constant amount lost in each equal time interval?
Answer:
A constant fraction decays over each half-life, so the absolute amount lost decreases as fewer nuclei remain.
Question 37 · Links 6.1.1.4
Why does 1 W equal 1 J/s?
Answer:
Power is energy transferred per second, so the units follow directly from P = E/t.
Question 38 · Links 6.2.1.2
A circuit transfers 24 C in 8.0 s. What current does the mathematical model predict?
Answer:
I = Q/t = 24 / 8.0 = 3.0 A.
Question 39 · Links 6.3.1.1
Why is density unchanged when a uniform block is cut in half?
Answer:
Mass and volume both halve, so their ratio remains the same.
Question 40 · Links 6.5.4.1.2
Why must average speed use total distance divided by total time?
Answer:
An unweighted average of different speeds can ignore unequal time intervals and give the wrong journey average.
Question 41 · Links 6.6.1.2
A timing method records 20 oscillations in 5.0 s. Find frequency and period.
Answer:
Frequency = 20 / 5.0 = 4.0 Hz; period = 1 / 4.0 = 0.25 s.
Question 42 · Links 6.1.2.2
A machine is 75% efficient and takes 400 J. Find useful output and dissipated energy.
Answer:
Useful output = 0.75 × 400 = 300 J; dissipated energy = 400 − 300 = 100 J.
Question 43 · Links 6.3.2.3
Which model should calculate energy to melt ice already at its melting point?
Answer:
Use E = mL, because the energy causes a state change rather than a temperature rise.
Question 44 · Links 6.5.3
Why must a 4 cm extension become 0.04 m when k is in N/m?
Answer:
Matching units are required in F = ke; leaving centimetres would make the calculated force 100 times too large.
Question 45 · Links 6.6.1.2
Why does measuring ten wavelengths reduce relative length uncertainty?
Answer:
The measured length is larger, while the absolute reading uncertainty is similar; division then gives a better wavelength estimate.
Question 46 · Links 6.3.1.1
Why does a method need both repeat readings and a check for zero error?
Answer:
Repeats help assess random variation; a zero error can shift every reading consistently and is not removed by averaging.
Question 47 · Links 6.4.2.3
Why should background counts be removed before finding a source's half-life?
Answer:
Background does not decay with the source; leaving it in distorts the apparent halving pattern.
Question 48 · Links 6.5.4.2.2
Why does testing F = ma require controlling one variable while changing another?
Answer:
It isolates the predicted force-acceleration or mass-acceleration relationship instead of mixing their effects.
Question 49 · Links 6.2.4.3
How do P = VI and cable loss = I²R explain Grid efficiency together?
Answer:
At a given transmitted power, higher voltage means lower current, which reduces heating loss in the cables.
Question 50 · Links 6.1.3
Why can equations support an energy-resource choice without deciding it alone?
Answer:
They quantify output, efficiency and costs, while reliability, environmental effects and social priorities also require evidence and judgement.

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