Free Praxis 8005 Science Practice Test

1. Earth is closer to the Sun during those months, so the Northern Hemisphere receives more heat.
2. Earth's axis is tilted, so the Northern Hemisphere receives sunlight at a higher angle and for more hours each day. ✓
3. Earth spins faster during those months, so each day collects more sunlight.
4. The Sun moves closer to the Northern Hemisphere during those months.

Answer: B. Earth's axis is tilted about 23.5 degrees from the plane of its orbit, so through the year each hemisphere leans toward or away from the Sun. In June the Northern Hemisphere leans toward the Sun and receives sunlight at a higher angle and for more hours per day, which raises temperatures. Distance from the Sun is not the cause of the seasons: Earth's orbit is nearly circular, and both hemispheres are the same distance from the Sun at any moment.

• Earth is closer to the Sun during those months, so the Northern Hemisphere receives more heat.: Treats orbital distance as the cause of the seasons; axial tilt changes the angle and the duration of sunlight, and the orbit is too nearly circular to drive seasons.
• Earth spins faster during those months, so each day collects more sunlight.: Confuses the rate of rotation with the angle of sunlight; the spin sets day and night, not the seasonal heating of a hemisphere.
• The Sun moves closer to the Northern Hemisphere during those months.: Treats the Sun as leaving the center of the solar system; the Sun does not approach one hemisphere, Earth's tilted axis does the work.

1. Erosion, then weathering, then deposition
2. Weathering, then deposition, then erosion
3. Weathering, then erosion, then deposition ✓
4. Deposition, then erosion, then weathering

Answer: C. Weathering breaks rock into smaller pieces such as loose sand grains, erosion transports that material from one place to another, and deposition drops it in a new location. In the scenario the breaking loose is weathering, the carrying down the valley is erosion, and the settling on the riverbank is deposition.

• Erosion, then weathering, then deposition: Orders transport before breakdown; breaking rock into loose grains is weathering, and erosion is the movement that follows it.
• Deposition, then erosion, then weathering: Reverses the whole sequence; material has to break down and then be moved before it can be deposited anywhere.
• Weathering, then deposition, then erosion: Places settling before transport; grains are dropped only after moving wind or water has carried them.

1. Clouds and the atmosphere dim different parts of the Moon.
2. The Moon rotates so that different parts of its surface light up each night.
3. As the Moon orbits Earth, observers see different portions of its sunlit half. ✓
4. Earth's shadow falls across a different amount of the Moon each week.

Answer: C. Half of the Moon is always lit by the Sun. As the Moon orbits Earth, the angle between the Sun, the Moon, and an observer on Earth changes, so the observer sees different fractions of the sunlit half, which produces the phases. Earth's shadow reaches the Moon only during a lunar eclipse, and eclipses do not occur every month.

• Earth's shadow falls across a different amount of the Moon each week.: Confuses phases with eclipses; Earth's shadow falls on the Moon only during a lunar eclipse, which does not happen every month.
• The Moon rotates so that different parts of its surface light up each night.: Assumes the Moon lights itself; the Sun always lights half the Moon, and rotation does not change which half is lit.
• Clouds and the atmosphere dim different parts of the Moon.: Attributes a regular monthly cycle to weather; atmospheric dimming varies from night to night and cannot produce a repeating phase pattern.

Average daylight on the 21st of each month (values rounded for readability)
City (latitude)        | March 21    | June 21      | September 21 | December 21
Fairbanks, Alaska 65N  | 12 h 10 min | 21 h 50 min  | 12 h 12 min  | 3 h 40 min
Miami, Florida 26N     | 12 h 8 min  | 13 h 45 min  | 12 h 10 min  | 10 h 35 min

1. Seasonal differences in daylight are larger at higher latitudes. ✓
2. Daylight hours depend mainly on each city's longitude rather than its latitude.
3. Fairbanks receives more daylight than Miami in every month shown.
4. Daylight hours depend mainly on how far each city is from the Sun.

Answer: A. The table shows both cities near 12 hours of daylight at the equinoxes, but in June Fairbanks reaches about 21 hours 50 minutes while Miami reaches about 13 hours 45 minutes, and in December Fairbanks drops to about 3 hours 40 minutes while Miami stays near 10 hours 35 minutes. The swing between seasons is therefore much larger at the higher latitude, which is what axial tilt combined with latitude predicts.

• Fairbanks receives more daylight than Miami in every month shown.: Ignores the December row, where Fairbanks has far less daylight; a pattern that holds in three rows is not supported in the fourth.
• Daylight hours depend mainly on how far each city is from the Sun.: Applies the distance explanation for seasons to two cities that are essentially the same distance from the Sun at any moment.
• Daylight hours depend mainly on each city's longitude rather than its latitude.: Attributes daylight to east-west position; longitude shifts when noon occurs, while latitude drives the seasonal change in daylight.

1. Infiltration
2. Condensation ✓
3. Transpiration
4. Evaporation

Answer: B. Condensation is the change of water vapor into liquid water droplets, which is what happens when moist air cools as it rises and expands. Evaporation added the vapor to the air in the first place, transpiration is vapor released by plant leaves, and infiltration is water soaking into the ground.

• Evaporation: Names the step that put water into the air as vapor, not the cooling step that turns that vapor back into droplets.
• Transpiration: Attributes the vapor to plants; transpiration is water vapor released by leaves, not vapor cooling into cloud droplets.
• Infiltration: Confuses water soaking into soil with the formation of droplets in cooling air.

1. Igneous rock, formed when melted material cooled and hardened.
2. Metamorphic rock, formed when heat and pressure changed an existing rock.
3. Sedimentary rock, formed when melted rock cooled quickly at the surface.
4. Sedimentary rock, formed when loose sediment was compacted and cemented. ✓

Answer: D. Layered grains held together by cement are the signature of sedimentary rock, which forms when sediment is buried, compacted, and cemented by minerals carried in water. Fossils are also most common in sedimentary rock because the material was deposited at low temperature and pressure, conditions that usually preserve shells instead of melting or recrystallizing them.

• Igneous rock, formed when melted material cooled and hardened.: Explains the texture with cooling melt, but cementing loose grains into layers requires compaction and cementation, not cooling.
• Metamorphic rock, formed when heat and pressure changed an existing rock.: Invokes heat and pressure strong enough to re-form the rock, which would typically alter or destroy both the fossil and the loose grain texture.
• Sedimentary rock, formed when melted rock cooled quickly at the surface.: Names the right rock type with the wrong process; melting and cooling produce igneous rock, not cemented layers.

1. The Moon's phases repeat about every four weeks.
2. Identical fossil species are found in rock layers on continents now separated by an ocean. ✓
3. Earthquake and volcano locations outline narrow belts along plate edges. ✓
4. Rivers carry sediment toward the sea.
5. Ocean water is denser than fresh water.

Answers: B and C. Matching fossil species on continents separated by an ocean indicate that those landmasses were once joined and have since moved apart. Earthquake and volcano locations clustering in narrow belts along plate boundaries show where plates interact. Both lines of evidence are independent of the other three statements, which describe the Moon's orbit, a property of water, and a sediment transport process, none of which concern the movement of plates.

• The Moon's phases repeat about every four weeks.: Describes the Moon's orbit around Earth, which says nothing about whether the rocky plates of Earth's surface move.
• Ocean water is denser than fresh water.: Compares the densities of two kinds of water, a property of water rather than evidence about moving plates.
• Rivers carry sediment toward the sea.: Describes sediment transport on the surface, which does not show that continents drift.

1. The volume of water poured over each tray
2. The slope at which each tray is set
3. Whether the soil surface is covered by grass or left bare ✓
4. The mass of soil collected at the bottom of each tray

Answer: C. The independent variable is the factor the investigation deliberately changes, which here is grass cover: one tray is bare and the other is planted. The mass of soil washed off is the dependent variable, because it is the outcome that is measured. Water volume and slope are controlled variables, held the same in both trays so the comparison isolates the effect of the grass.

• The mass of soil collected at the bottom of each tray: Names the outcome that is measured, which makes it the dependent variable rather than the factor the setup deliberately changes.
• The volume of water poured over each tray: Names a condition deliberately held the same in both trays, which makes it a controlled variable rather than the tested factor.
• The slope at which each tray is set: Names another condition held constant across the trays; matching slopes are what keep the comparison fair.

Average annual temperature, one inland town (rounded to 0.1 C)
Decade | 1960s | 1970s | 1980s | 1990s | 2000s | 2010s
Average annual temperature (C) | 11.2 | 11.4 | 11.6 | 12.0 | 12.4 | 12.9

1. The long-term average annual temperature at this location rose over the six decades shown. ✓
2. Every single year in the 2010s was warmer than every single year in the 1960s.
3. One unusually cold winter in the 2010s would show that the trend in the table is wrong.
4. The 2020s will average exactly 13.4 degrees Celsius at this location.

Answer: A. The table reports decade averages, and each decade is warmer than the one before it, which supports a statement about the long-term average. It does not describe individual years, so it cannot show that every year in one decade beat every year in another, and a single cold winter is a weather event rather than a test of a multi-decade average. The table also reports past averages, so it cannot establish an exact future value.

• Every single year in the 2010s was warmer than every single year in the 1960s.: Reads a decade average as if it described each individual year; averages hide the year-to-year variation within a decade.
• One unusually cold winter in the 2010s would show that the trend in the table is wrong.: Treats one short-term weather event as a test of a multi-decade climate average, which operates on a different time scale.
• The 2020s will average exactly 13.4 degrees Celsius at this location.: Presents a straight-line guess as a measured prediction; the table reports past averages, not future values.

1. One plate slides beneath the other, producing a deep ocean trench.
2. One plate crumples the other upward, producing a coastal mountain range.
3. New seafloor forms as melted rock rises into the gap and cools. ✓
4. The two plates grind past each other sideways, producing shallow earthquakes.

Answer: C. Where two oceanic plates move apart, the boundary is divergent. The plates pull away from each other, melted rock rises from below to fill the gap, and the new material cools and hardens into ocean floor, which builds a mid-ocean ridge. A deep trench forms where one plate descends beneath another, sideways grinding is a transform boundary, and crumpled mountain ranges form where plates collide and crust is thickened.

• One plate slides beneath the other, producing a deep ocean trench.: Describes a convergent boundary where one plate descends; plates that move apart are not being pushed under each other.
• The two plates grind past each other sideways, producing shallow earthquakes.: Describes a transform boundary; sideways motion between plates does not open a gap for new seafloor to form.
• One plate crumples the other upward, producing a coastal mountain range.: Describes collision and crustal thickening; the plates in the question are separating rather than colliding.

1. Nucleus and cytoplasm
2. Chloroplast and mitochondrion ✓
3. Cell wall and cell membrane
4. Cell membrane and chloroplast

Answer: B. Chloroplasts contain the pigments that capture light energy for photosynthesis, and mitochondria release usable energy from food molecules through cellular respiration. The cell wall and cell membrane handle support and the movement of materials into and out of the cell, while the nucleus holds the genetic material and the cytoplasm is the region where the other structures are found.

• Cell wall and cell membrane: Confuses support and boundary structures with the two organelles that handle light energy and energy release.
• Nucleus and cytoplasm: Names the control center and the region that holds the cell's structures, neither of which captures light or releases energy from food.
• Cell membrane and chloroplast: Assigns energy release to the membrane, which controls what enters and leaves the cell rather than breaking down food molecules.

1. The number of petals on a flowering plant ✓
2. The tan color of skin after repeated sun exposure
3. The scars on a tree trunk where branches broke off
4. The language a child learns at home

Answer: A. An inherited trait is coded by genetic material passed from parents to offspring, and petal number in a plant species is controlled that way. The other three traits appear during an organism's life in response to its surroundings: sun exposure, physical damage, and learning from the environment.

• The tan color of skin after repeated sun exposure: Describes a change produced by exposure during life, which makes it an acquired trait rather than an inherited one.
• The scars on a tree trunk where branches broke off: Points to damage that happened during the tree's own life; damage of that kind is not coded in the genes passed to offspring.
• The language a child learns at home: Names a learned skill that depends on the surrounding environment, so it is acquired rather than inherited.

1. Green beetles survived and reproduced more often, so green coloring became more common in the population. ✓
2. The beetles needed to avoid being eaten, so they developed green color and passed it to their offspring.
3. Individual beetles changed color during their lifetimes to match the leaves.
4. The birds stopped eating beetles, so the beetles all became green by chance.

Answer: A. Variation in color already existed in the beetle population. Birds removed more of the beetles that stood out, so the beetles that blended in survived longer and left more offspring, and the proportion of green beetles in the population rose over generations. Selection acts on the variation that is present; the environment does not create the trait, and an individual beetle's color does not change during its life.

• Individual beetles changed color during their lifetimes to match the leaves.: Treats a change within one lifetime as the cause; an individual beetle's color does not shift, and changes acquired in life are not passed on.
• The beetles needed to avoid being eaten, so they developed green color and passed it to their offspring.: Assumes that need produces a heritable change; selection sorts the variation that already exists rather than generating it.
• The birds stopped eating beetles, so the beetles all became green by chance.: Replaces selection with chance and contradicts the premise that birds kept hunting; chance alone would not produce the same shift.

Energy available in one meadow food chain
Trophic level | Organisms | Energy available (kJ per square meter per year)
First (producers) | grasses and other plants | 20,000
Second | grasshoppers | 2,000
Third | birds that eat grasshoppers | 200

1. Matter is created at each trophic level as organisms grow.
2. Birds store most of the energy they consume as body mass.
3. Energy passes from one trophic level to the next with almost no loss.
4. Only a small fraction of the energy held in producers is available to the next trophic level. ✓

Answer: D. The producer level holds about 20,000 kilojoules per square meter per year, the grasshopper level about 2,000, and the bird level about 200, so roughly one tenth carries over at each step. Most of the energy that organisms take in is released as heat through their own life processes and is not passed along, which is why the amount of available energy drops sharply at each higher trophic level.

• Matter is created at each trophic level as organisms grow.: Treats growth as the creation of matter; organisms rearrange matter they take in, and the column that falls is available energy.
• Energy passes from one trophic level to the next with almost no loss.: Contradicts the roughly tenfold drop between adjacent levels that the data show.
• Birds store most of the energy they consume as body mass.: Assumes most consumed energy becomes body mass, when much of it is released as heat during the birds' life processes.

1. Energy flows through an ecosystem and is eventually released as heat. ✓
2. Energy in an ecosystem comes mainly from minerals in the soil.
3. Matter disappears when organisms die and decompose.
4. Energy is recycled by decomposers and reused by producers.
5. Matter cycles among organisms, the air, water, and soil. ✓

Answers: A and E. Matter such as carbon, nitrogen, and water moves in cycles: producers take it in, consumers pass it along food chains, and decomposers return it to air, water, and soil where producers can use it again. Energy behaves differently. It enters an ecosystem mainly as sunlight, moves through organisms, and much of it is released as heat at every step, so it flows through rather than cycling.

• Energy is recycled by decomposers and reused by producers.: Mixes the two quantities; decomposers recycle matter, while energy leaves the system as heat and is not reused.
• Matter disappears when organisms die and decompose.: Assumes matter is destroyed during decay; decomposition breaks dead tissue into substances that return to the environment.
• Energy in an ecosystem comes mainly from minerals in the soil.: Names minerals as the main energy source; minerals are matter, and ecosystems are powered mainly by sunlight.

1. The 3 percent salt dish, which receives the largest amount of salt
2. The 0 percent salt dish, which measures germination without salt added ✓
3. The temperature and light level, since they stay the same in every dish
4. Every dish that received salt, since those dishes are compared with one another

Answer: B. A control group is the untreated baseline that the treated conditions are compared against. Here the 0 percent dish receives no salt, so it shows how the seeds germinate under the same conditions without the factor being tested. The 1, 2, and 3 percent dishes are treatment groups, and temperature and light are controlled variables because they are held constant rather than being a separate group.

• The 3 percent salt dish, which receives the largest amount of salt: Picks the treatment furthest from the baseline; a control group is the untreated comparison, not the largest dose.
• Every dish that received salt, since those dishes are compared with one another: Treats the treated dishes as the comparison; a control group is the untreated baseline the treatments are measured against.
• The temperature and light level, since they stay the same in every dish: Describes controlled variables, which are conditions held constant in every group, not a baseline group.

1. Plants carry out photosynthesis at all times and never carry out respiration.
2. Plants carry out cellular respiration at all times, while photosynthesis happens only when light is available. ✓
3. Plants do not need oxygen because they make their own food.
4. Plants release oxygen at night and take in carbon dioxide only during the day.

Answer: B. Plants, like other living things, carry out cellular respiration continuously, taking in oxygen and releasing carbon dioxide as they release usable energy from food. Photosynthesis requires light, so it occurs only in the light, when the plant takes in carbon dioxide and releases oxygen. During daylight photosynthesis is usually faster than respiration, so the plant releases more oxygen than it uses, but respiration does not stop.

• Plants carry out photosynthesis at all times and never carry out respiration.: Removes respiration from the picture; plant cells respire continuously, using oxygen and releasing carbon dioxide.
• Plants release oxygen at night and take in carbon dioxide only during the day.: Swaps the gas exchange in both directions; in the light, photosynthesis takes in carbon dioxide and releases oxygen.
• Plants do not need oxygen because they make their own food.: Confuses making food with using it; the living cells of a plant still need oxygen to release energy from that food.

1. Grasshoppers pass through a pupal stage, while butterflies do not.
2. Grasshoppers pass through egg, nymph, and adult stages, while butterflies add a pupal stage. ✓
3. Both insects hatch as adults and grow larger without changing form.
4. Both insects pass through egg, larva, pupa, and adult stages.

Answer: B. Grasshoppers develop through incomplete metamorphosis: eggs hatch into nymphs that already resemble small adults and gradually develop wings as they molt. Butterflies develop through complete metamorphosis: eggs hatch into larvae, the larvae form a pupa, and the adult emerges from the pupa. The body form changes much more dramatically in the butterfly's cycle.

• Grasshoppers pass through a pupal stage, while butterflies do not.: Attributes a pupal stage to grasshoppers and removes it from butterflies; it is the butterfly that forms a pupa.
• Both insects pass through egg, larva, pupa, and adult stages.: Applies complete metamorphosis to both insects; grasshoppers develop gradually through nymph stages instead.
• Both insects hatch as adults and grow larger without changing form.: Claims that neither insect changes form, ignoring the nymph stages of grasshoppers and the larva and pupa stages of butterflies.

Average seedling height after 14 days, in centimeters
Condition | Trial 1 | Trial 2 | Trial 3
Full sunlight | 12.1 | 11.9 | 12.3
Partial shade | 9.4 | 9.8 | 9.2
Near-total darkness | 3.1 | 3.4 | 2.9

1. The table shows that light level is the only factor that affects seedling height.
2. Seedlings grown in full sunlight were tallest in every trial. ✓
3. Seedlings in near-total darkness were tallest, which shows that light stops growth.
4. The three conditions cannot be compared because the trials had different results.

Answer: B. The full sunlight group reached about 12 centimeters in all three trials, the partial shade group about 9 centimeters, and the darkness group about 3 centimeters, so the sunlight group was tallest in each trial and the trials within each condition agree closely with one another. The table tests light level only, and the repeated trials make the comparison more reliable rather than less.

• Seedlings in near-total darkness were tallest, which shows that light stops growth.: Reads the table backwards; the darkness row holds the lowest values in all three trials.
• The three conditions cannot be compared because the trials had different results.: Treats small differences among trials as a barrier to comparison, when each condition's three trials are consistent and comparable.
• The table shows that light level is the only factor that affects seedling height.: Overstates the evidence; the investigation varied light level and says nothing about water, soil, or temperature.

Organisms counted per square meter in a pond study, plus relative algae cover
Organism or measure | Before fish were added | Two years after fish were added
Water fleas (small grazers) | 420 | 90
Diving beetle larvae | 60 | 25
Filamentous algae (relative cover) | 15 | 80

1. After fish were added, the number of small grazers fell and the algae cover rose. ✓
2. Fish ate beetle larvae rather than water fleas, which left the algae unaffected.
3. The number of water fleas rose after the fish were added.
4. Algae cover fell over the same period in which water fleas increased.

Answer: A. The counts move in opposite directions: water fleas drop from 420 to 90 per square meter while filamentous algae rise from a relative cover of 15 to 80 over the same two years. Reporting those two measured changes is what the data support directly. The remaining statements either reverse the direction of a measured change or assert which prey the fish preferred, which the counts do not address.

• Fish ate beetle larvae rather than water fleas, which left the algae unaffected.: Asserts a feeding preference the counts do not show, and denies the rise in algae that the table does show.
• The number of water fleas rose after the fish were added.: Reverses the direction of change in the water flea row, which falls from 420 to 90.
• Algae cover fell over the same period in which water fleas increased.: Reverses both trends; the algae row rises while the water flea row falls.

1. A spoonful of sugar dissolves completely in water.
2. A solid is crushed into a fine powder.
3. A new solid settles out and the mixture warms without any outside heating. ✓
4. A liquid is warmed until it boils.

Answer: C. A chemical change produces one or more new substances with different properties. A solid appearing where there was none before the mixing, together with a temperature rise that was not supplied from outside, indicates that new substances formed and that energy was released by a reaction. Crushing, boiling, and dissolving change the form or the arrangement of a substance while its identity stays the same.

• A solid is crushed into a fine powder.: Describes a change in particle size only; the material keeps its identity, so no new substance is produced.
• A liquid is warmed until it boils.: Describes a change of state; boiling water is still water, so the change is physical.
• A spoonful of sugar dissolves completely in water.: Describes forming a mixture; the sugar can be recovered by evaporating the water, which shows no new substance formed.

1. It decreases, because the tablet dissolves in the water.
2. It stays the same, because gases have no mass.
3. It increases, because the fizzing releases energy inside the jar.
4. It stays the same, because the gas produced cannot escape. ✓

Answer: D. In a closed system, matter is conserved: the tablet and water are rearranged into new substances, including a gas, but nothing leaves the jar, so the total mass is unchanged. Dissolving keeps the tablet's mass inside the jar, and the gas that forms does have mass, which is why an open container would read lower.

• It decreases, because the tablet dissolves in the water.: Treats dissolving as a loss of matter; the tablet's mass is still in the jar and the gas it produces stays trapped as well.
• It stays the same, because gases have no mass.: Reaches the right answer for the wrong reason; the gas has mass and is simply sealed inside the jar.
• It increases, because the fizzing releases energy inside the jar.: Confuses energy with matter; releasing energy does not add mass to the closed system.

1. The push is larger than friction, which is why the wagon keeps speeding up.
2. No forces act on the wagon, because it is moving steadily.
3. The forces on the wagon are balanced, so its motion does not change. ✓
4. The forces are unbalanced, which is why the wagon is slowing down.

Answer: C. A steady speed in a straight line means the wagon's velocity is not changing, which happens when the forces on it add up to zero: the forward push is cancelled by friction and air resistance. Balanced forces do not mean the object must be still, only that its motion does not change. Unbalanced forces would make the wagon speed up, slow down, or change direction.

• The push is larger than friction, which is why the wagon keeps speeding up.: Would produce a changing speed, but the wagon's speed is stated as steady at 2 meters per second.
• No forces act on the wagon, because it is moving steadily.: Treats constant velocity as the absence of forces; a push and friction are both acting even when they cancel out.
• The forces are unbalanced, which is why the wagon is slowing down.: Contradicts the steady speed given in the question; unbalanced forces change motion, and the motion here is not changing.

Distance from the starting line, in meters
Time (s) | 0 | 2 | 4 | 6 | 8
Runner A | 0 | 6 | 12 | 18 | 24
Runner B | 0 | 3 | 6 | 9 | 12

1. Runner A covers 3 meters each second, so Runner A is moving faster than Runner B. ✓
2. Both runners have the same speed, because both started at 0 meters.
3. Runner A is accelerating, because the distance keeps increasing.
4. Runner B is faster, because Runner B covers fewer meters in the same time.

Answer: A. Runner A's distance rises by 6 meters every 2 seconds, which is 3 meters per second, while Runner B's rises by 3 meters every 2 seconds, which is 1.5 meters per second. Equal distance in equal time intervals means steady speed, and the larger distance covered in the same time means the greater speed. Both starting at 0 meters only shows that they started from the same place.

• Runner B is faster, because Runner B covers fewer meters in the same time.: Turns the comparison around; covering fewer meters in the same time means a lower speed.
• Both runners have the same speed, because both started at 0 meters.: Uses a shared starting point as evidence about speed, but speed depends on how much distance is covered in each unit of time.
• Runner A is accelerating, because the distance keeps increasing.: Reads steady increase as acceleration; the same distance is covered in each equal time interval, which means constant speed.

1. A series circuit keeps working when one of its bulbs is removed.
2. A conductor resists the movement of charge more than an insulator does.
3. A closed circuit provides a complete path for electric current. ✓
4. A parallel circuit provides more than one path for current. ✓
5. A battery stores light energy in its terminals.

Answers: C and D. Current moves only when there is a complete loop, which is what a closed circuit provides. In a parallel circuit the branches give current more than one path, so removing one branch still leaves a complete path through the others. A series circuit has a single path, so removing one bulb breaks the loop for every bulb, conductors let charge move more readily than insulators, and a battery stores chemical energy rather than light energy.

• A series circuit keeps working when one of its bulbs is removed.: Ignores the single path in a series circuit; removing one bulb opens the loop for every component in it.
• A conductor resists the movement of charge more than an insulator does.: Reverses the definitions; conductors let charge move more readily than insulators do.
• A battery stores light energy in its terminals.: Names the wrong stored form; a battery stores chemical energy and converts it rather than storing light.

1. Release the pendulum from a larger angle in the later trials so that it swings longer.
2. Change the string length and the bob at the same time so the effect is easier to see.
3. Keep the same bob and the same release angle in every trial while changing only the string length. ✓
4. Count a different number of swings in each trial so that every trial takes the same time.

Answer: C. A fair test changes one factor and holds everything else constant. The student wants to know the effect of string length, so length should be the only factor that differs between trials. Using the same bob and the same release angle in every trial removes the other two differences, which means any change in the swing time can be attributed to length. Changing several factors at once leaves the cause of the difference impossible to identify.

• Change the string length and the bob at the same time so the effect is easier to see.: Keeps the confound in place; with two factors changing together, the cause of any difference in swing time cannot be identified.
• Release the pendulum from a larger angle in the later trials so that it swings longer.: Introduces a second change partway through, so release angle differs across trials and competes with length.
• Count a different number of swings in each trial so that every trial takes the same time.: Adjusts the measurement method instead of the design; timing must be done the same way in every trial for the results to be comparable.

1. The two balls hit the ground at the same time, so the metal ball does not land first. ✓
2. The metal ball lands first, because gravity pulls harder on the ball with more mass.
3. The plastic ball lands first, because lighter objects speed up faster as they fall.
4. The plastic ball lands first, because it moves through the air more easily.

Answer: A. Gravity pulls on the metal ball with a larger force, but the metal ball also has more mass, and the acceleration a force produces falls as mass rises. The two effects cancel, so both balls speed up at the same rate and reach the ground together. Air resistance is what makes real objects fall at slightly different rates, and it depends on shape and size rather than on mass alone.

• The metal ball lands first, because gravity pulls harder on the ball with more mass.: Confuses a larger gravitational force with a larger acceleration; the bigger force acts on a bigger mass, so the acceleration is unchanged.
• The plastic ball lands first, because it moves through the air more easily.: Attributes a timing difference to air resistance, which the setup states makes no measurable difference here.
• The plastic ball lands first, because lighter objects speed up faster as they fall.: Reverses the same misconception; the rate at which falling objects speed up does not depend on their mass.

1. Sound 1 travels faster than Sound 2 because its frequency is higher.
2. Sound 1 has a higher pitch, and Sound 2 is louder. ✓
3. Both sounds have the same pitch, because amplitude does not change pitch.
4. Sound 1 is louder, and Sound 2 has a higher pitch.

Answer: B. For sound, frequency determines pitch and amplitude determines loudness. Sound 1 has the higher frequency, so it has the higher pitch, and Sound 2 has the larger amplitude, so it is louder. The amplitude and frequency of a sound wave are separate properties, and in the same air both sounds travel at essentially the same speed.

• Sound 1 is louder, and Sound 2 has a higher pitch.: Swaps the two properties; frequency sets pitch while amplitude sets loudness.
• Both sounds have the same pitch, because amplitude does not change pitch.: States a true rule about amplitude but ignores the stated difference in frequency, which is what sets pitch.
• Sound 1 travels faster than Sound 2 because its frequency is higher.: Treats frequency as a measure of speed; in the same air, sounds of different frequency travel at essentially the same speed.

1. The chemical reaction destroyed a small amount of matter.
2. The tablet's mass was converted into energy during the reaction.
3. Some matter left the cup as gas, so the open system lost mass. ✓
4. The balance lost accuracy because of the bubbles in the water.

Answer: C. The cup was open, so the gas produced by the fizzing could escape into the room and carry matter away with it. The missing 2.4 grams is matter that became gas and left, which is why the reading dropped. In a chemical change, matter is rearranged rather than created or destroyed; sealing the cup would give a reading that stays constant.

• The chemical reaction destroyed a small amount of matter.: Treats matter as something a chemical change can destroy; the matter was rearranged and part of it left as gas.
• The tablet's mass was converted into energy during the reaction.: Invokes a nuclear-scale conversion, which does not occur in a fizzing tablet reaction.
• The balance lost accuracy because of the bubbles in the water.: Blames the instrument when the missing mass matches the gas that escaped from the open cup.

Temperature of a beaker of ice and water that is heated at a steady rate and stirred
Time (min) | 0 | 2 | 4 | 6 | 8 | 10
Temperature (C) | -8 | 0 | 0 | 0 | 4 | 11

1. The ice is melting between 8 and 10 minutes, which is when the temperature rises fastest.
2. The temperature stays at 0 degrees Celsius because water cannot be heated above that point.
3. Between 2 and 6 minutes the ice is melting, so the energy added goes into changing state instead of raising the temperature. ✓
4. Heating stopped between 2 and 6 minutes, because the temperature does not change there.

Answer: C. Heating is steady throughout, so the flat section between 2 and 6 minutes at 0 degrees Celsius shows that energy is going into melting the ice rather than raising the temperature. During a change of state, added energy breaks the bonds that hold the solid together instead of increasing the average motion of the particles. Once the ice has melted, the temperature rises again, reaching 4 degrees Celsius at 8 minutes and 11 degrees Celsius at 10 minutes.

• Heating stopped between 2 and 6 minutes, because the temperature does not change there.: Ignores the premise of steady heating; energy keeps flowing in during melting while the temperature holds.
• The ice is melting between 8 and 10 minutes, which is when the temperature rises fastest.: Moves the melting stage to the warm-up period; a rising temperature means liquid water is being warmed, not ice melting.
• The temperature stays at 0 degrees Celsius because water cannot be heated above that point.: Treats 0 degrees Celsius as a ceiling; the reading climbs above 0 degrees Celsius once the ice has melted.