All of Practical Skills Flashcards
(32 cards)
Why should you keep the ruler close to the object when measuring length?
To avoid parallax error. Your eye should be in line with the point on the ruler for the same reason.
What type of error is parallax error?
Parallax error is a random error—it varies each time you take a measurement.
How can you reduce parallax error when measuring things like spring extension?
Use set squares (right-angled triangles, even cardboard) to align with the ruler, and ensure the ruler is vertical with another set square between it and the table.
What is the typical resolution of a ruler or metre rule?
1 millimetre—the smallest difference it can measure.
What is a major source of random error when using a stopwatch? How do you reduce it?
Reaction time. Reduce it by doing repeat measurements and calculating a mean.
Which instruments are commonly used to measure the thickness of a wire in Young modulus or resistivity experiments?
Vernier calipers and micrometers.
How do you avoid parallax error with analogue instruments?
Keep your eye in line with the needle. Some instruments have mirrors behind the scale to assist.
What is meant by ‘full scale deflection’ (FSD) and how do you choose the appropriate one?
FSD is the maximum measurement an instrument can make (e.g., 1, 2, 5, 10, 50, 100). Choose the smallest FSD greater than your expected maximum. E.g., for 6V, use a 10V meter.
What is the typical resolution of a micrometer and how do you calibrate it?
0.01 mm (1/100th mm). Close jaws using the ratchet—if it reads 0.00 mm, it’s calibrated. Otherwise, correct for zero error.
What is zero error in a micrometer and how do you account for it?
A systematic error if it doesn’t read 0.00 mm when closed. Subtract (or add if negative) this from all measurements.
How do you read a micrometer measurement (example)?
If the thimble shows 1.5 mm and the barrel shows 24 (0.24 mm), the total is 1.74 mm. Adjust for zero error accordingly.
How do Vernier calipers work?
The zero on the slide shows mm. The Vernier scale adds tenths (or sometimes twentieths). A line that aligns on both scales gives the additional measurement.
How can Vernier calipers be used to measure the depth of an object?
Use the depth rod on the end. Insert it into the tube and read the scale normally.
Why is there always some uncertainty in measurements, even without parallax or zero error?
Due to rounding. Example: with 1°C resolution, you must judge whether it’s closer to 27 or 28°C.
What is the uncertainty of a measurement in chemistry and physics with a 1°C resolution?
Chemistry: ±0.5°C (half resolution). Physics: often ±1°C (full resolution) to be more cautious.
What is the uncertainty in a digital instrument reading 5.32V?
±0.01V (same as the resolution of the last digit).
How do you calculate uncertainty in a mean value?
Find the range (max - min), divide by 2 for absolute uncertainty.
How do you use error bars and lines of worst fit to find uncertainty in gradient?
Draw a line of worst fit crossing all bars. Gradient difference from the best-fit line gives the uncertainty.
How can you alternatively use lines of worst fit to find gradient uncertainty?
Draw two worst-fit lines (max and min gradients). Mean of both = gradient. Half the range = uncertainty.
How do you find total uncertainty when adding/subtracting two values?
Add their absolute uncertainties.
How does ruler movement affect uncertainty?
If ruler is movable: uncertainty = resolution. If fixed ends are used: uncertainty = 2 × resolution.
What is absolute uncertainty and how does it differ from percentage uncertainty?
Absolute uncertainty has a unit (e.g., mm). Percentage uncertainty is (absolute uncertainty / value) × 100.
What do you do with uncertainties when multiplying or dividing?
Convert to percentage uncertainties and add them together.
What happens to uncertainty when you take a square root?
Halve the percentage uncertainty of the original value.
