OCR GCSE Physics Paper 3

P1 - What was the main discovery from Rutherford's alpha scattering experiment

:: Almost all alpha particles passed straight through, but a few deflected at large angles, proving a tiny, positively charged nucleus surrounded by mostly empty space.

P1 - What is the approximate order of magnitude for the size/radius of an atom

:: $1 \times 10^{-10}\text{ m}$.

P1 - State the equation for density including standard units.

$$\text{Density } (kg/m^3) = \frac{\text{mass } (kg)}{\text{volume } (m^3)}$$

P1 - How does mass behave during a physical change of state

:: Mass is conserved because the number and type of particles remain unchanged.

P1 - What is the main difference between a physical change and a chemical change

:: A physical change is reversible and the substance recovers its original properties, whereas a chemical change forms new substances and cannot be easily reversed.

P1 - Define specific heat capacity (SHC)

The amount of thermal energy required to raise the temperature of $1\text{ kg}$ of a substance by $1\,^{\circ}\text{C}$.

P1 - Define specific latent heat.

The thermal energy required to change the state of $1\text{ kg}$ of a substance with no change in temperature.

P1 - What is the difference between latent heat of fusion and latent heat of vaporisation

:: Fusion is for solid to liquid (melting); vaporisation is for liquid to gas (boiling/evaporation).

P1 - How does increasing the temperature of a fixed mass of gas at constant volume increase its pressure

:: Particles gain kinetic energy and move faster, colliding with container walls more frequently and with greater force.

P1 - State the qualitative relationship between pressure and volume for a gas at constant temperature.

Pressure and volume are inversely proportional ($p V = \text{constant}$).

P1 - Why does doing mechanical work on a gas (e.g. using a bicycle pump) increase its temperature

:: Work done transfers energy to the kinetic store of the gas particles, raising the average kinetic energy and thus temperature.

P1 - Why does atmospheric pressure decrease with increasing altitude

:: Fewer air particles exist higher up, resulting in less weight of air pushing down on a unit area.

P1 - State the equation used to calculate pressure due to a column of liquid.

$\text{Pressure } (Pa) = \text{height } (m) \times \text{density } (kg/m^3) \times g \ (N/kg)$.

P1 - Explain how liquid pressure causes an upthrust force on a partially submerged object.

Pressure increases with depth, producing a greater upward force on the bottom surface than the downward force on the top surface.

P1 - Under what condition will an object float in a fluid

:: When upthrust is equal to or greater than the object's total weight (or its density is less than the fluid's density).

P1 - Why does a submerged object experience a net upward force

:: The pressure at the bottom of the object is higher than at the top, creating a net upward force (upthrust).

P2 - What is the difference between a scalar and a vector quantity

:: A scalar has magnitude only; a vector has both magnitude and direction.

P2 - How is displacement distinguished from distance

:: Distance is a scalar measuring path length; displacement is a vector measuring distance in a straight line with direction.

P2 - State the equation linking acceleration, velocity change, and time.

$\text{Acceleration } (m/s^2) = \frac{\text{change in velocity } (m/s)}{\text{time } (s)}$.

P2 - How do you calculate distance travelled from a velocity-time graph

:: Calculate the area enclosed under the curve/line and the x-axis.

P2 - State Newton's First Law of Motion.

An object remains at rest or at constant velocity unless acted upon by a resultant external force.

P2 - State Newton's Second Law equation in words.

$\text{Force } (N) = \text{mass } (kg) \times \text{acceleration } (m/s^2)$.

P2 - Define inertial mass.

The ratio of force over acceleration ($m = F/a$); a measure of how difficult it is to change an object's velocity.

P2 - State Newton's Third Law of Motion.

When two objects interact, they exert equal and opposite forces on each other.

P2 - Explain why an object moving in a circle at constant speed is accelerating.

Its direction changes continuously, so its velocity changes, meaning there is an acceleration towards the center.

P2 - State the momentum equation.

$\text{Momentum } (kg\,m/s) = \text{mass } (kg) \times \text{velocity } (m/s)$.

P2 - Explain terminal velocity in terms of forces acting on a falling object.

As speed increases, drag increases until drag equals weight, resultant force becomes zero, and acceleration stops.

P2 - Define Hooke's Law.

Extension of a spring is directly proportional to the force applied, provided the limit of proportionality is not exceeded ($F = kx$).

P2 - What is the difference between elastic and plastic deformation

:: Elastic returns to its original shape when forces are removed; plastic retains a permanent deformation.

P2 - State the equation for elastic potential energy stored in a stretched spring.

$\text{Energy } (J) = 0.5 \times \text{spring constant } (N/m) \times (\text{extension } (m))^2$.

P2 - Define weight and state its standard SI unit.

The force of gravity acting on a mass, measured in Newtons ($N$).

P2 - State the equation for the moment of a force.

$\text{Moment } (Nm) = \text{force } (N) \times \text{perpendicular distance from pivot } (m)$.

P2 - What condition must be met for a system to be in rotational equilibrium

:: Total clockwise moments equal total anticlockwise moments about a pivot.

P2 - How do gears act as force multipliers

:: A small gear driving a larger gear increases the turning effect (moment) due to a larger radius/distance.

P2 - State the equation linking work done, force, and distance moved.

$\text{Work done } (J) = \text{force } (N) \times \text{distance along line of action } (m)$.

P2 - Define power in terms of energy transfer.

The rate at which energy is transferred or work is done ($\text{Power } = \frac{\text{Work done}}{\text{time}}$).

P2 - State the kinetic energy equation. ::

$$\text{Kinetic energy } (J) = 0.5 \times \text{mass } (kg) \times (\text{speed } (m/s))^2$$

P2 - State the gravitational potential energy equation.

GPE (J) = Mass (kg) x Gravitiational Field Strength (N / kg) x Height (m)

P3 - What type of charge transfer causes static electricity on insulators

:: Transfer of negatively charged electrons by friction.

P3 - What happens to the electric field strength around a charged object as distance increases

:: The electric field strength decreases.

P3 - Define electric current.

The rate of flow of electrical charge ($I = \frac{Q}{t}$)

P3 - State the equation linking charge flow, current, and time.

$$\text{Charge flow } (C) = \text{current } (A) \times \text{time } (s)$$

P3 - What is potential difference

:: The energy transferred per unit charge between two points in a circuit ($V = \frac{E}{Q}$).

P3 - State Ohm's Law equation.

$$\text{Potential difference } (V) = \text{current } (A) \times \text{resistance } (\Omega)$$

P3 - Describe the $I\text{--}V$ characteristic of an Ohmic conductor.

A straight line passing through the origin; current is directly proportional to potential difference (constant resistance).

P3 - Why does the resistance of a filament lamp increase as current increases

:: Higher current increases temperature, causing ions in the metal lattice to vibrate more, increasing electron collisions.

P3 - Describe the $I\text{--}V$ characteristic of a semiconductor diode.

Current only flows in the forward direction when potential difference exceeds a threshold; infinite resistance in reverse direction

P3 - How does thermistor resistance change with temperature

:: Resistance decreases as temperature increases.

P3 - How does LDR resistance change with light intensity

:: Resistance decreases as light intensity increases.

P3 - How does current behave in a single series circuit loop

:: Current has the same value at any point in the loop.

P3 - What happens to total resistance when resistors are added in series vs. in parallel

:: In series, total resistance increases; in parallel, total resistance decreases.

P3 - State the equation linking electrical power, potential difference, and current.

$$\text{Power } (W) = \text{potential difference } (V) \times \text{current } (A)$$

P3 - State the equation linking power, current, and resistance.

$$\text{Power } (W) = (\text{current } (A))^2 \times \text{resistance } (\Omega)$$

P4 - What is the difference between a permanent magnet and an induced magnet

:: A permanent magnet produces its own field; an induced magnet becomes magnetic only when placed in a magnetic field.

P4 - What direction do magnetic field lines always point

:: From the North pole to the South pole.

P4 - What evidence proves the Earth's core is magnetic

:: A magnetic dipping compass points towards magnetic North/South regardless of location.

P4 - Describe the magnetic field pattern around a straight current-carrying wire.

Concentric circles centered on the wire perpendicular to its direction.

P4 - How can the strength of a solenoid's magnetic field be increased

:: Increase the current, add an iron core, or increase the number of turns on the coil.

P4 - What is Fleming's Left-Hand Rule used for and what do the fingers represent

:: Used for the motor effect: Thumb = Force/Motion, First finger = Magnetic Field (N-to-S), Second finger = Current (positive to negative).

P4 - State the equation for force on a conductor in a magnetic field.

$\text{Force } (N) = \text{magnetic flux density } (T) \times \text{current } (A) \times \text{length } (m)$.

P4 - What is the function of a split-ring commutator in a d.c. motor

:: Reverses the direction of current in the coil every half-turn to keep the motor rotating in one direction.

P4 - Define electromagnetic induction.

Inducing a potential difference across a conductor by moving it through a magnetic field or exposing it to a changing magnetic field

P4 - What is Lenz's Law regarding induced current

:: The induced current flows in a direction such that its magnetic field opposes the original change that created it.

P4 - What is the structural difference between an alternator and a dynamo

:: An alternator uses slip rings to produce alternating current (a.c.); a dynamo uses a split-ring commutator to produce direct current (d.c.).

P4 - State the transformer ratio equation.

$$\frac{\text{Primary p.d. } (V_p)}{\text{Secondary p.d. } (V_s)} = \frac{\text{Turns in primary } (N_p)}{\text{Turns in secondary } (N_s)}$$

P4 - State the equation for 100% efficient transformers linking power in primary and secondary coils.

$V_p \times I_p = V_s \times I_s$.

P4 - How does a dynamic microphone convert sound waves into electrical signals

:: Pressure variations in sound waves move a diaphragm attached to a coil inside a magnetic field, inducing an alternating potential difference.

P9 - What is a zero error in measuring instruments and how is it corrected

:: An instrument giving a non-zero reading when the true value is zero; correct by subtracting the false initial reading from all data.

P9 - Why should an electrical circuit be turned off between readings during PAG 6 experiments

:: To prevent circuit components from heating up, which would alter their resistance and invalidate results.

P9 - How can heat loss be minimized during a specific heat capacity experiment (PAG 5)

:: Insulate/lag the block or liquid beaker and cover with a lid.

P9 - What is the difference between repeatable and reproducible data

:: Repeatable means the same experimenter gets similar results using the same method; reproducible means another person gets similar results using different equipment/methods.

P9 - What causes parallax error when measuring length with a ruler

:: Reading a scale at an angle rather than at eye level perpendicular to the scale.

P9 - Why are light gates preferred over stopwatches for high-speed acceleration tests

:: Light gates eliminate human reaction time errors, significantly increasing precision and accuracy.

P9 - How do you measure the density of an irregularly shaped solid object

:: Measure mass on a balance, submerge object in a eureka/displacement can filled with water, and measure the volume of displaced water using a measuring cylinder.

P9 - Define accuracy versus precision in scientific measurements.

Accuracy is how close a measurement is to the true value; precision is how close repeated measurements are to each other

P4 - What are permanent magnets?

Magnets that are always magnetic and always have fixed north and south poles.

P4 - How are induced magnets produced?

By stroking magnetic materials with a permanent magnet to align their domains in the same direction.

P4 - Which three metals are common magnetic materials that can be induced?

Iron, Nickel, and Cobalt.

P4 - What indicates a greater magnetic field strength in a field diagram?

A greater concentration (density) of magnetic field lines in an area.

P4 - How does a plotting compass show the magnetic field around a magnet?

The compass needle aligns with the magnetic field lines, showing the field's direction at that point.

P4 - Which magnetic pole is located above Northern Canada near the geographic North Pole?

Earth's magnetic South Pole.

P4 - How do current and distance affect the strength of a magnetic field around a wire?

Increasing current increases field strength; increasing distance from the wire decreases field strength.

P4 - What is a solenoid?

A coil of wire carrying a current that produces a magnetic field similar in shape to a bar magnet.

P4 - Why does inserting an iron core inside a solenoid increase its field strength?

Magnetic field lines pass through iron much more easily than through air.

P4 - Name four factors that affect the field strength of a solenoid.

Size of current, length of coil, cross-sectional area, and number of turns (coils).

P4 - Why does a current-carrying wire experience a force when placed in a magnetic field?

The magnetic field around the wire interacts with the magnetic field between the magnets.

P4 - What is Magnetic Flux Density and what unit is it measured in?

The number of flux lines per square metre, measured in Tesla ($T$).

P4 - Why does a coil of wire rotate in a simple electric motor?

Forces act in opposite directions (one up, one down) on opposite sides of the current-carrying coil.

P4 - What is alternating current (a.c.)?

Current that constantly changes direction, creating a constantly changing magnetic field.

P4 - Why will a transformer NOT work with a direct current (d.c.) supply?

Direct current creates a constant magnetic field, so no potential difference is induced in the secondary coil.

P4 - What is the difference between a step-up and a step-down transformer?

Step-up has more secondary turns to increase potential difference;