Flashcards · YPH11 · Topic 3

Practical Skills in Physics I flashcards

18 cards on Topic 3, subtopics 3.3 to 3.5. Pick a subtopic or study them all.

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Resolution of a metre rule, Vernier calipers and a micrometer screw gauge: Metre rule: 1 mm. Vernier calipers: 0.1 mm. Micrometer: 0.01 mm.
Uncertainty in a single reading: Half the resolution of the instrument (for example ±0.5 mm on a metre rule).
Correcting a zero error: A zero error is systematic: every reading is shifted by the same amount. Subtract a positive zero error; add the size of a negative one. Repeating does not remove it.
How should safety be written in a plan?: As a pair: the specific hazard and its precaution (for example, a falling mass: a sand tray and feet kept clear).
When are repeat readings useful, and when not?: Useful where there is random scatter (hand timing, a wire’s diameter). Not useful for a zero error or a digital reading that does not change.
Controls in a plan for resistance against length of a wire: Same wire (material and diameter), low current, short switch-on time, so the temperature stays the same.

Micrometer: sleeve 2.0 mm, thimble 45, zero error +0.03 mm. Reading?: 2.0 + 0.45 = 2.45 mm; 2.45 − 0.03 = 2.42 mm
Reading Vernier calipers: Main-scale reading before the Vernier zero + 0.1 mm × the number of the Vernier mark that lines up. For example 32 mm and the seventh mark: 32.7 mm.
Four things to check in another student’s results: Number of readings (at least six for a graph), range, significant figures matching the instrument’s resolution, and any inconsistent readings.
Improvements to avoid parallax and misreadings: A set square to keep a rule vertical; a pointer or fiducial marker and eye level with the scale; a micrometer instead of a ruler for a thin wire.
What should you do with an inconsistent reading?: Check it against the trend, re-measure and repeat. Do not simply delete it.

Uncertainty from repeated readings, and percentage uncertainty: Half the range: (largest − smallest) ÷ 2. Percentage uncertainty = uncertainty ÷ value × 100%.
Times of 3.2 s, 3.4 s and 3.3 s. Mean and percentage uncertainty?: Mean 3.3 s, half range 0.1 s, so 0.1 ÷ 3.3 × 100 = 3.0%
Random vs systematic error: Random: readings scatter either side of the true value; repeating and averaging reduces it. Systematic: every reading is shifted the same way; repeating does not remove it.
Precise vs accurate: Precise: repeated readings agree closely. Accurate: close to the true value.
How should you find a gradient from a graph?: Draw a large triangle on the best-fit line using two points far apart that are not data points, and give the gradient a unit.
A straight line that should pass through the origin has an intercept. What does it suggest?: A systematic error (such as a zero error) in one of the measurements.
Graph of R against L for a wire has gradient 7.3 Ω m⁻¹; the wire’s area is 7.07 × 10⁻⁸ m². Resistivity?: Gradient = ρ/A, so ρ = 7.3 × 7.07 × 10⁻⁸ = 5.2 × 10⁻⁷ Ω m