ACT Science Quiz: Identifying Sources Of Error

What this quiz covers

This quiz focuses on Identifying Sources Of Error, giving you a quick way to practice the rules, question types, and explanations that matter most for ACT Science.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. Remain unaffected.
2. Show increased variability.
3. Be lower than the actual concentration.
4. Be higher than the actual concentration. (correct answer)

Explanation: Reading burette levels from below eye level creates a systematic error due to parallax, where the meniscus appears higher than its actual position. This causes the experimenter to consistently record larger volumes than actually dispensed, leading to an overestimation of the titrant volume used. Since concentration calculations involve dividing by the volume of titrant, overestimating this volume results in calculating a higher concentration than the true value. This systematic bias affects all readings in the same direction, distinguishing it from random measurement errors.

Question 2

1. be longer than the actual reaction time
2. be shorter than the actual reaction time
3. have no effect on the measured time
4. vary randomly around the actual time (correct answer)

Explanation: Human reaction time affects both the start and stop of timing, introducing random error that causes measurements to vary unpredictably around the actual reaction time. The researcher's reflexes will sometimes be faster and sometimes slower when pressing the stopwatch, and these delays don't consistently favor either starting too early/late or stopping too early/late. This creates variability where some measurements will be slightly longer than the actual time and others slightly shorter, with the errors being random rather than systematic. The effect is particularly noticeable for short reactions like 2 seconds, where human reaction time (typically 0.1-0.3 seconds) represents a significant fraction of the total measured time.

Question 3

1. Wind changes, which alter sound travel time inconsistently and therefore create random variation in measured speed. (correct answer)
2. Using a measuring tape, which has perfect accuracy and eliminates all distance uncertainty.
3. Computing $v=2d/t$, which always doubles the true speed and creates a systematic error.
4. Standing 50.0 m away, which guarantees the echo time is long enough to remove reaction-time error entirely.

Explanation: Wind changes create the most significant source of variability by altering sound travel time inconsistently across trials. Wind can either aid or oppose sound transmission, causing the sound to travel faster or slower than in still air, which directly affects the measured echo time and calculated speed. Since wind direction and speed vary unpredictably during outdoor trials, this creates random variation in the calculated speeds that is much larger than other potential error sources. The wind effect on sound transmission is the primary factor causing trial-to-trial differences in measured sound speed.

Question 4

1. Lamp heating the nearest beaker, changing temperature and confounding light intensity with reaction rate. (correct answer)
2. Using baking soda, which prevents photosynthesis by removing dissolved carbon dioxide.
3. Counting bubbles by eye, which creates a constant offset but does not affect comparisons across distances.
4. Repeating twice, which doubles systematic error and makes the trend appear stronger than it is.

Explanation: Lamp heating of the nearest beaker creates the most significant error source by changing temperature and confounding light intensity with reaction rate effects. The heat from the lamp raises the water temperature in the closest beaker, increasing the metabolic rate and photosynthesis rate due to temperature effects rather than just light intensity. This creates systematic bias because the nearest beaker experiences both maximum light intensity and elevated temperature, making it impossible to determine whether increased bubble production results from light or heat. The confounding of these two variables fundamentally compromises the experimental design.

Question 5

1. Repeating three times, which introduces extra error compared with taking a single careful reading.
2. Using a tall cylinder, which increases specific gravity by increasing hydrostatic pressure.
3. Reading from slightly above the meniscus, causing tiny random parallax errors that cancel across solutions.
4. Different solution temperatures, changing density and causing systematic differences unrelated to sugar concentration. (correct answer)

Explanation: Different solution temperatures create the most significant error source by changing fluid density independently of sugar concentration. Since hydrometer readings depend on the density difference between the solution and the hydrometer's calibrated density scale, temperature variations cause systematic density changes that are unrelated to sugar content. Warmer solutions have lower density than cooler ones, leading to systematically different specific gravity readings even for identical sugar concentrations. This temperature effect introduces systematic bias that can easily overwhelm the sugar concentration effect being measured.

Question 6

1. Using the same brand of soil, which contaminates all pots with identical nutrients and invalidates comparisons.
2. Measuring height with a ruler, which is too precise and therefore introduces systematic bias.
3. Planting seeds at 2 cm depth, which guarantees all seeds germinate at the same time.
4. Watering with an unmarked cup, creating random daily water differences that can strongly affect growth. (correct answer)

Explanation: Watering with an unmarked cup creates the most significant error source by introducing random daily water differences that strongly affect plant growth. Since water availability is a critical factor for plant development, the uncontrolled variation in daily watering amounts (some plants receiving significantly more or less than the intended 50 mL) would create large random differences in growth rates that could easily mask or distort the fertilizer effects. This watering variability represents a major uncontrolled variable that directly impacts the dependent variable being measured.

Question 7

1. All be too low, because subtracting a nonzero blank reduces reported absorbance values systematically. (correct answer)
2. All be too high, because a dyed blank forces the instrument to add extra absorbance.
3. Become random, because blank errors affect only some concentrations unpredictably.
4. Be unchanged, because blank choice affects only the 0.00 mM standard.

Explanation: Using a dyed blank instead of pure water causes all measured absorbances to be systematically too low. When the spectrophotometer zeros using a blank that already contains dye, it subtracts that dye's absorbance from all subsequent measurements. Since absorbance values are calculated relative to the blank, each standard's measured absorbance becomes (true absorbance - blank absorbance), resulting in systematically reduced values across the entire calibration curve. This creates a consistent negative bias in all absorbance measurements.

Question 8

1. remain unaffected by drop variance.
2. be consistently higher.
3. be consistently lower.
4. show increased variability. (correct answer)

Explanation: Dropping the sphere inconsistently would cause viscosity measurements to show increased variability because the initial conditions of each drop affect the sphere's motion and timing through the viscous liquid. Inconsistent dropping includes variations in initial position, release angle, rotational motion, and initial velocity, all of which influence how the sphere moves through the liquid before reaching terminal velocity. These variable starting conditions mean that some trials will have longer or shorter measured times due to differences in the initial motion phase rather than true differences in viscosity. This procedural inconsistency introduces random error that causes the calculated viscosity values to scatter around the true value, reducing measurement precision.

Question 9

1. Using a chipped meterstick end, producing a consistent length bias and therefore a systematic period shift.
2. Human reaction time when starting and stopping the stopwatch, creating random trial-to-trial timing differences. (correct answer)
3. Timing 20 oscillations instead of 1, which increases random timing error by a factor of 20.
4. Measuring length to the bottom of the bob, which is the correct reference point for pendulum length.

Explanation: Human reaction time when starting and stopping the stopwatch creates the most significant error source. Each trial requires the experimenter to visually detect when the bob passes the center point and react to start/stop the stopwatch, introducing random timing differences of typically 0.1-0.3 seconds per measurement. Since each period calculation involves two reaction-time errors (start and stop), this creates substantial trial-to-trial variability in the measured periods. The chipped meterstick creates systematic error but affects all measurements equally, while timing 20 oscillations actually reduces random error by averaging.

Question 10

1. Heating with a cycling hot plate, causing overshoot and making the observed melting temperature systematically too high. (correct answer)
2. Using a capillary tube, which prevents wax from melting and therefore lowers the measured melting point.
3. Recording the first transparency, which is unrelated to melting and always gives random temperatures.
4. Comparing two waxes in the same bath, which forces both to have identical melting points.

Explanation: The cycling hot plate creates the most significant error source by causing temperature overshoot that makes the observed melting temperature systematically too high. When the hot plate cycles on and off, the temperature rises in jumps rather than smoothly, often overshooting the true melting point before the experimenter can observe and record the transition. This temperature overshoot means the recorded melting point is higher than the actual transition temperature. The cycling heating pattern introduces systematic positive bias that consistently elevates all melting point measurements.

Question 11

1. Measuring at a constant speed.
2. Using a digital viscometer.
3. Mixing liquids with different densities.
4. Temperature fluctuations during measurement. (correct answer)

Explanation: Temperature fluctuations during viscosity measurement would most significantly affect result consistency because viscosity is highly temperature-dependent for most liquids. As temperature changes, the liquid's viscosity changes accordingly, causing measured values to vary even when using the same sample under otherwise identical conditions. These temperature variations introduce random error since room temperature typically fluctuates unpredictably, leading to scattered results rather than systematic bias. Maintaining constant temperature is crucial for reproducible viscosity measurements since even small temperature changes can produce significant viscosity variations.

Question 12

1. Unchanged, because equivalence depends only on molarity, not on volume delivered.
2. Too large, because actual added volume is less than the recorded volume at every step.
3. More variable only, because a consistent syringe bias creates random scatter in pH readings.
4. Too small, because actual added volume exceeds the recorded volume at every step. (correct answer)

Explanation: The equivalence point volume would be measured as too small because the actual delivered volume exceeds the recorded volume at every step. Since the syringe delivers 1.0 mL when set to 0.9 mL, the student consistently adds more NaOH than recorded. The equivalence point occurs when the actual moles of NaOH equal the moles of HCl, but this happens at a smaller recorded volume than expected because more base is being delivered per increment. The systematic over-delivery means fewer recorded increments are needed to reach neutralization.

Question 13

1. show random variations unrelated to temperature.
2. be slower than expected at higher temperatures.
3. be unaffected by temperature changes.
4. be faster than expected at higher temperatures. (correct answer)

Explanation: Not accounting for temperature variations would cause the calculated speed of sound to be faster than expected at higher temperatures because sound travels faster in warmer air. The speed of sound increases approximately 0.6 m/s for each degree Celsius increase in air temperature due to increased molecular motion in warmer air. If students use a standard value for the speed of sound (typically measured at 20°C) but conduct their experiment at a higher temperature, their calculated distance will be based on the assumption of a slower sound speed. Since they measure the actual (shorter) time for the echo to return in warmer air, their calculation will yield a speed that appears faster than the expected reference value measured at standard conditions.

Question 14

1. Become more variable only, because bubbles change mass and volume by equal percentages each trial.
2. Decrease, because bubbles increase displaced volume while the measured mass stays nearly unchanged. (correct answer)
3. Stay the same, because bubbles are mostly air and do not change any measured quantities.
4. Increase, because bubbles add mass without affecting the displaced water volume.

Explanation: Air bubbles clinging to the metal surface would cause the measured density to decrease. The bubbles increase the apparent volume of displaced water (making Vf larger) while the actual mass of the metal remains unchanged. Since density equals mass divided by volume, the artificially increased volume leads to a calculated density that is lower than the true value. The bubble effect systematically reduces density measurements because the air displaces additional water without contributing to the metal's mass.

Question 15

1. Time only one trial, because repeating trials increases random error in the final acceleration.
2. Increase the track angle to 30° so the cart moves faster and looks more impressive.
3. Measure the 1.00 m distance with a shorter ruler to avoid any meterstick calibration issues.
4. Use photogates or video timing instead of a handheld stopwatch to reduce reaction-time uncertainty. (correct answer)

Explanation: Using photogates or video timing instead of a handheld stopwatch would most effectively reduce measurement error. Human reaction time introduces significant random uncertainty (typically ±0.1-0.3 seconds) when manually starting and stopping timing, which becomes a large percentage error for the relatively short travel times in this experiment. Automated timing systems eliminate this reaction-time variability and provide much more precise time measurements. Increasing the track angle or using shorter rulers would not address the primary source of timing uncertainty.

Question 16

1. Starting timing at mixing, which is incorrect because timing should begin after the reaction ends.
2. Recording every 10 seconds, which is too frequent and therefore reduces accuracy of the reaction.
3. Using a 100 mL cylinder, which automatically rounds volumes to the nearest 10 mL.
4. Not equalizing water levels, causing a systematic pressure difference and biased volume readings at each time point. (correct answer)

Explanation: Not equalizing water levels creates the most significant error source by introducing a systematic pressure difference that biases all volume readings. When the water level inside the graduated cylinder differs from the trough level, the pressure difference affects the apparent gas volume collected, leading to consistently incorrect measurements at each time point. This systematic error in pressure equilibration makes all gas volume readings inaccurate by a consistent amount, fundamentally compromising the measurement of reaction rate. The pressure effect is much more significant than minor temperature changes during the experiment.

Question 17

1. Timing errors during measurement.
2. Using a faulty accelerometer.
3. Inaccurate distance measurement.
4. Incorrect initial velocity recording. (correct answer)

Explanation: Incorrectly recording an initial velocity that is lower than the actual value would cause an overestimation of calculated acceleration. Since acceleration is determined from the change in velocity over time (a = Δv/Δt), underestimating the initial velocity makes the calculated velocity change (Δv) appear larger than it actually was. This artificially inflated velocity change leads to a higher calculated acceleration value. The error systematically affects the fundamental measurement used in acceleration calculations, unlike timing or distance errors which might introduce different types of bias depending on their direction.

Question 18

1. Have increased precision.
2. Exhibit random error.
3. Be unaffected by the drift.
4. Show systematic error. (correct answer)

Explanation: Calibration drift in a pH meter introduces systematic error because the instrument's readings shift consistently in one direction over time. This occurs when the meter's internal reference gradually changes, causing all subsequent measurements to be offset by a consistent amount from the true pH values. Unlike random errors that vary unpredictably around the true value, systematic errors from calibration drift create a persistent bias that affects all measurements similarly. This distinguishes calibration problems from random measurement variations that would decrease precision without creating consistent bias.

Question 19

1. Reusing the same beakers without washing, allowing leftover salt to systematically increase concentration in later trials. (correct answer)
2. Leaving beakers on a sunny windowsill, allowing temperature and light changes to alter rusting rates across trials.
3. Using tap water to rinse clips, introducing minerals that always slow rusting equally in all beakers.
4. Reading the graduated cylinder slightly above or below the meniscus, causing small random volume differences.

Explanation: Reusing the same beakers without washing between trials is the most significant error source. This creates systematic error because salt from previous trials accumulates in the beakers, progressively increasing the actual NaCl concentration beyond the intended levels. The accumulated salt would cause later trials to show artificially faster rusting times, creating a bias that systematically distorts the concentration-rusting relationship. While temperature variations and volume measurement errors introduce variability, the systematic concentration bias from unwashed beakers has a much larger and more consistent effect on results.

Question 20

1. Type of gas used.
2. Volume of water not measured accurately.
3. Gas collection tube not sealed properly. (correct answer)
4. Temperature of the water not controlled.

Explanation: Improper sealing of the gas collection tube would most significantly affect accuracy because it allows gas to escape, leading to underestimation of the actual volume of gas produced. When gas leaks from the collection system, the measured volume represents only a fraction of the total gas generated by the reaction, creating systematic error in stoichiometric calculations. This directly compromises the fundamental measurement the experiment is designed to obtain. While temperature and water volume affect the conditions and calculations, they can be measured and corrected for, unlike gas loss which cannot be easily detected or quantified.