Pearson Science Double Award Practical 7: Physics Contexts

Double Award Physics practical questions connect measurements to models and uncertainty. This note maps the explicit 4SD0 practical points, plus the required experimental current-voltage treatment, without importing separate-Physics investigations.

Motion

Investigate an everyday object's motion using measured position and time. A toy car can pass light gates, cross marked distances recorded on video or be timed across a long path. Define the origin and reference point on the object. A longer interval reduces the fractional effect of stopwatch reaction time.

Plot distance against time for speed from gradient, or velocity against time for acceleration from gradient and displacement from area. Keep ramp angle, release point, surface and car constant when comparing a chosen independent variable. Release without an extra push.

Force and extension

Clamp the material securely beside a ruler and measure original length from a fixed reference. Add known loads, let oscillations settle and record loaded length. Calculate extension as loaded minus original length. Convert mass to force using $F=mg$.

Use small increments across a safe range for springs, metal wires or rubber bands. Plot force against extension and identify the initial linear region associated with Hooke's law. Unload to test elastic recovery. Wear eye protection, keep clear of falling masses and do not exceed a safe extension.

Current-voltage behaviour

Connect the ammeter in series and voltmeter in parallel across the component. Use a variable resistor or adjustable supply to vary voltage. Record paired current and voltage values, reversing polarity where appropriate for a diode.

For a resistor, switch off between readings if constant temperature is required. A filament lamp's temperature change is part of its non-ohmic behaviour, but uncontrolled overheating can still damage it. Begin on a safe meter range and reduce range only when readings permit.

Plot current against voltage with clear sign conventions. Shape, gradient and symmetry distinguish resistor, lamp and diode behaviour. Do not calculate one resistance and assume it applies across a curved graph.

Refraction and refractive index

Place a rectangular glass block on paper and trace its outline. Draw an incident ray and normal, use pins or a ray box to establish the path, then mark emergent direction before removing the block. Join marks with thin lines and measure angles from the normal.

Repeat for several incidence angles and calculate $n=\sin i/\sin r$. A graph of $\sin i$ against $\sin r$ can use gradient as refractive index if axes are chosen accordingly. A semicircular block can isolate refraction at one surface when the ray passes through its centre. A triangular prism demonstrates direction changes but does not automatically provide the same simple parallel-face geometry.

Thermal transfer

For conduction, compare rods of equal dimensions with identical indicators or measure temperature change at matched positions. For convection, use visible tracer movement in a safely heated fluid. For radiation, compare matched surfaces at the same temperature and geometry, using cooling rate or detector response.

Change one property at a time. Control mass, dimensions, starting temperature, distance and surrounding conditions. Hot apparatus requires heatproof surfaces and safe handling. Because convection and radiation can occur alongside conduction, design geometry and insulation to reduce competing pathways.

Density

Measure mass with a zeroed balance. For a regular solid, measure dimensions and calculate volume. For an irregular sinking object, use displacement in a measuring cylinder or displacement can. Remove bubbles, submerge fully and read the meniscus at eye level.

Calculate $\rho=m/V$ in consistent units. Repeat dimensions at different positions if the object is not perfectly uniform. Avoid displacement for soluble, absorbent or reactive objects unless a safe alternative liquid is justified.

Magnetic fields

Place a bar magnet beneath paper and use a plotting compass at a grid of positions. Mark the direction of the compass north end and join a smooth field pattern with arrows from north to south outside the magnet. Iron filings can reveal pattern density but not direction.

Repeat for like and unlike pole pairs with unchanged spacing. Two unlike flat pole faces close together can create an approximately uniform region shown by parallel, evenly spaced lines. Keep magnets away from sensitive devices and avoid confusing compass needle direction with force on a south pole.

Radiation penetration

Use a simulation where appropriate or follow controlled-source procedures. Measure background count for a defined time. Keep source-detector distance, alignment and counting time fixed. Record count without absorber, then with paper, aluminium or suitable shielding.

Subtract background before comparison. Radioactive counts fluctuate randomly, so use long counting intervals or repeats. Minimise exposure time, maximise distance, use tongs and shielding, and never handle a source directly. The aim is comparative penetration, not unsafe pursuit of a zero count.

Physics context map

Worked application

To determine glass refractive index, trace a block and direct rays at five incidence angles. Mark each path with two well-separated points, draw thin lines and measure $i$ and $r$ from normals. Calculate sines without rounding and plot $\sin i$ vertically against $\sin r$ horizontally. The best-fit gradient estimates $n$. Repeat uncertain angles after replacing the block on its outline. Thick rays and short pin spacing increase angular uncertainty, so use narrow beams or distant pins. A line not passing through the origin may indicate systematic misalignment rather than a new optical law.

Common misconceptions

• “One stopwatch interval is enough for short motion.” Lengthen the interval and repeat.
• “Spring length equals extension.” Subtract original length.
• “An ammeter goes in parallel.” It must carry the circuit current in series.
• “Resistance is constant for every component.” Lamps and diodes are non-ohmic.
• “Optical angles are measured from the block face.” Measure from the normal.
• “A finer thermometer isolates one thermal pathway.” Geometry must control competing transfers.
• “Iron filings show field direction.” A plotting compass supplies direction.
• “Raw radiation count is source count.” Subtract background.

Assessment guidance

State the measured quantities, reference points, apparatus connections and controlled geometry. In graph work, link gradient or area to the relevant physical quantity with units. Extension, temperature change and displaced volume require raw initial and final readings. Optical methods need normals, thin lines and repeated angles. Thermal methods must separate intended and competing pathways. Field maps require direction evidence. Radiation comparisons need background correction, fixed geometry, random-count treatment and source-specific safety. Do not import investigations from points explicitly reserved for separate Physics.

Retrieval practice

1. Plan motion and force-extension investigations.
2. Draw a valid current-voltage circuit and measurement sequence.
3. Determine refractive index from ray and graph methods.
4. Compare conduction, convection and radiation designs.
5. Choose density methods for regular and irregular objects.
6. Map magnetic fields and compare radiation penetration safely.

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