19 free Electrical Aptitude questions from our 150-question bank, grouped by content domain. Each answer explains why the right option is right — and why every wrong option is wrong.
If , what is the value of ?
Answer: B
4: Found as ; , so .
8: Correct. and , so .
13: Subtracted the inputs first and found ; evaluate each output, then subtract.
14: Added instead of subtracting it.
means find each output separately and then subtract; it is not .
Which graph shows the line ?
Answer: A
Graph A: Correct. The line crosses the -axis at and rises 1 for every 3 to the right, through .
Graph B: Shows : it rises 3 for each 1 across, so the slope was taken as 3.
Graph C: Shows : right slope, but it crosses the -axis at .
Graph D: Shows : right intercept, but the line falls instead of rising.
A slope of means rise 1, run 3: a shallow line. A slope of 3 is steep. Check the intercept and the steepness separately.
The table shows values from a linear relationship between and . What is the value of when ?
| x | y |
|---|---|
| 0 | 5 |
| 2 | 11 |
| 4 | 17 |
| 6 | 23 |
Answer: A
20: Correct. rises 6 for every 2 units of , which is 3 per unit, so .
23: This is the value at , not at .
29: This is the next entry in the pattern, at .
35: Treated the increase of 6 as the change for each 1 unit of ; the -values go up by 2.
Divide the change in by the change in to get the rate per unit before you predict a value between table rows.
Which statement about the formula is true?
Answer: B
If is greater than 8, then is greater than 0.: Reversed: for , , which is less than 0.
If is less than 8, then is greater than 0.: Correct. means , so and .
If is less than 2, then is less than 0.: For , ; small values give positive .
If is greater than 4, then is less than 0.: Used 4 as the cutoff; for , , which is positive.
Find the input where the output equals the cutoff value, then decide which side of it gives the larger output.
What is the next number in the pattern ?
Answer: B
15: Repeated the last difference, 4; the differences grow by 1 each time.
16: Correct. The differences are 1, 2, 3, 4, so the next difference is 5: .
17: Added 6, skipping the difference of 5.
22: Doubled 11; only the first two steps look like doubling.
When the differences themselves change by a constant amount, extend the list of differences first.
Which expression is equivalent to ?
Answer: C
: Multiplied only first terms and last terms; the middle terms and are missing.
: Sign error on the middle term: .
: Correct. .
: Added and ; the inner product is .
Multiply every term in the first binomial by every term in the second, then combine like terms.
If , , and , what is the value of ?
Answer: D
: Two sign errors: took as and subtracted instead of .
: Took as ; a negative number squared is positive, so .
9: Found but then subtracted 3; subtracting adds 3.
15: Correct. and , so .
Put each negative value in parentheses before squaring, and remember that subtracting a negative product adds it.
1In 1890 nearly 41 million Americans, about 65 percent of the population, lived in rural areas. City residents had received free mail delivery to their homes since 1863, but farm families still had to travel to a post office, sometimes miles away, to collect their letters and newspapers. John Wanamaker, who served as Postmaster General from 1889 to 1893, wrote in 1891 that rural people needed the same connection to the wider world and proposed free delivery for them.
2Congress moved slowly. A bill introduced in 1892 was rejected as too costly. On March 3, 1893, Congress finally set aside money for an experiment, but the next Postmaster General, Wilson S. Bissell, declined to pursue it, claiming that far more money would be needed. His successor, William L. Wilson, took office on March 1, 1895. After Congress added more funds, rural free delivery began on October 1, 1896, in Charles Town, Halltown, and Uvilla, in Wilson's home state of West Virginia. Within a year, 44 routes were operating in 29 states, and during the experimental years customers sent in more than 10,000 petitions asking for routes.
3A route required passable roads, so rural free delivery encouraged communities to improve their roads. Mailboxes were another concern. At first, farmers used lard pails, syrup cans, and soap or cigar boxes. Specifications issued in 1901 called for a weatherproof metal box, 6 by 8 by 18 inches, mounted at a height the carrier could reach and easy to open with one gloved hand. Beginning in 1902, customers had to use an approved box to receive service.
4Rural free delivery became a permanent service on July 1, 1902, when about 8,500 rural carriers served the country. Carriers supplied their own transportation, usually a horse and wagon. They also sold stamps and money orders and handled registered letters, acting as traveling post offices. In 1906 the word "free" was dropped from the service's name, and by 1929 improved roads had led almost all carriers to switch to motor cars. The number of post offices in the nation peaked at 76,945 in 1901 and declined steadily after that.
Based on the passage, the number of post offices most likely declined after 1901 because
Answer: C
more farm families had to travel to collect mail: Reversed: paragraphs 1 and 4 say rural delivery brought mail to farm homes, so families traveled less to a post office.
Congress stopped paying for rural routes: Contradicted: service became permanent in 1902, the year the decline began.
rural carriers made many small offices unnecessary: Correct. The decline began just as delivery became permanent (1902), and carriers acted "as traveling post offices," so fewer local offices were needed.
approved mailboxes made stamps unnecessary: Mailboxes held mail; carriers still sold stamps, so this has no support.
Support an inference with timing and stated functions from the passage, and check that a proposed cause comes before its effect.
1In 1890 nearly 41 million Americans, about 65 percent of the population, lived in rural areas. City residents had received free mail delivery to their homes since 1863, but farm families still had to travel to a post office, sometimes miles away, to collect their letters and newspapers. John Wanamaker, who served as Postmaster General from 1889 to 1893, wrote in 1891 that rural people needed the same connection to the wider world and proposed free delivery for them.
2Congress moved slowly. A bill introduced in 1892 was rejected as too costly. On March 3, 1893, Congress finally set aside money for an experiment, but the next Postmaster General, Wilson S. Bissell, declined to pursue it, claiming that far more money would be needed. His successor, William L. Wilson, took office on March 1, 1895. After Congress added more funds, rural free delivery began on October 1, 1896, in Charles Town, Halltown, and Uvilla, in Wilson's home state of West Virginia. Within a year, 44 routes were operating in 29 states, and during the experimental years customers sent in more than 10,000 petitions asking for routes.
3A route required passable roads, so rural free delivery encouraged communities to improve their roads. Mailboxes were another concern. At first, farmers used lard pails, syrup cans, and soap or cigar boxes. Specifications issued in 1901 called for a weatherproof metal box, 6 by 8 by 18 inches, mounted at a height the carrier could reach and easy to open with one gloved hand. Beginning in 1902, customers had to use an approved box to receive service.
4Rural free delivery became a permanent service on July 1, 1902, when about 8,500 rural carriers served the country. Carriers supplied their own transportation, usually a horse and wagon. They also sold stamps and money orders and handled registered letters, acting as traveling post offices. In 1906 the word "free" was dropped from the service's name, and by 1929 improved roads had led almost all carriers to switch to motor cars. The number of post offices in the nation peaked at 76,945 in 1901 and declined steadily after that.
Which of the following statements about early rural delivery is true, based on the passage?
Answer: A
Rural carriers did more than deliver mail to farm homes.: Correct. Paragraph 4: carriers "sold stamps and money orders and handled registered letters, acting as traveling post offices."
Postmaster General Bissell started the first rural routes.: Paragraph 2 says Bissell declined to pursue the experiment; service began under Wilson.
All 44 early routes began on the same day.: Only the West Virginia routes began on October 1, 1896; the 44 routes were operating "within a year."
The word "free" was dropped from the name in 1902.: Near-miss date: 1902 is when service became permanent; "free" was dropped in 1906.
Test each statement against its paragraph; a date or person that is close but not exact makes an option false.
1In 1890 nearly 41 million Americans, about 65 percent of the population, lived in rural areas. City residents had received free mail delivery to their homes since 1863, but farm families still had to travel to a post office, sometimes miles away, to collect their letters and newspapers. John Wanamaker, who served as Postmaster General from 1889 to 1893, wrote in 1891 that rural people needed the same connection to the wider world and proposed free delivery for them.
2Congress moved slowly. A bill introduced in 1892 was rejected as too costly. On March 3, 1893, Congress finally set aside money for an experiment, but the next Postmaster General, Wilson S. Bissell, declined to pursue it, claiming that far more money would be needed. His successor, William L. Wilson, took office on March 1, 1895. After Congress added more funds, rural free delivery began on October 1, 1896, in Charles Town, Halltown, and Uvilla, in Wilson's home state of West Virginia. Within a year, 44 routes were operating in 29 states, and during the experimental years customers sent in more than 10,000 petitions asking for routes.
3A route required passable roads, so rural free delivery encouraged communities to improve their roads. Mailboxes were another concern. At first, farmers used lard pails, syrup cans, and soap or cigar boxes. Specifications issued in 1901 called for a weatherproof metal box, 6 by 8 by 18 inches, mounted at a height the carrier could reach and easy to open with one gloved hand. Beginning in 1902, customers had to use an approved box to receive service.
4Rural free delivery became a permanent service on July 1, 1902, when about 8,500 rural carriers served the country. Carriers supplied their own transportation, usually a horse and wagon. They also sold stamps and money orders and handled registered letters, acting as traveling post offices. In 1906 the word "free" was dropped from the service's name, and by 1929 improved roads had led almost all carriers to switch to motor cars. The number of post offices in the nation peaked at 76,945 in 1901 and declined steadily after that.
If a farm township wanted a route in 1897 but its only road was often impassable, what would it most likely need first?
Answer: D
A motor car for the carrier: Carriers supplied their own transportation, and motor cars became common only by 1929.
More than 10,000 petitions: 10,000 was the national total of petitions over the experimental years, not a requirement for one township.
A new post office in town: The passage does not list a new post office as a requirement; delivery brought mail from existing offices.
A road a carrier could travel: Correct. Paragraph 3: "A route required passable roads," so the township would first need a usable road.
Apply the stated requirement to the new case; distractors borrow real numbers or facts from other parts of the passage.
According to the passage, in which state did rural free delivery begin?
1In 1890 nearly 41 million Americans, about 65 percent of the population, lived in rural areas. City residents had received free mail delivery to their homes since 1863, but farm families still had to travel to a post office, sometimes miles away, to collect their letters and newspapers. John Wanamaker, who served as Postmaster General from 1889 to 1893, wrote in 1891 that rural people needed the same connection to the wider world and proposed free delivery for them.
2Congress moved slowly. A bill introduced in 1892 was rejected as too costly. On March 3, 1893, Congress finally set aside money for an experiment, but the next Postmaster General, Wilson S. Bissell, declined to pursue it, claiming that far more money would be needed. His successor, William L. Wilson, took office on March 1, 1895. After Congress added more funds, rural free delivery began on October 1, 1896, in Charles Town, Halltown, and Uvilla, in Wilson's home state of West Virginia. Within a year, 44 routes were operating in 29 states, and during the experimental years customers sent in more than 10,000 petitions asking for routes.
3A route required passable roads, so rural free delivery encouraged communities to improve their roads. Mailboxes were another concern. At first, farmers used lard pails, syrup cans, and soap or cigar boxes. Specifications issued in 1901 called for a weatherproof metal box, 6 by 8 by 18 inches, mounted at a height the carrier could reach and easy to open with one gloved hand. Beginning in 1902, customers had to use an approved box to receive service.
4Rural free delivery became a permanent service on July 1, 1902, when about 8,500 rural carriers served the country. Carriers supplied their own transportation, usually a horse and wagon. They also sold stamps and money orders and handled registered letters, acting as traveling post offices. In 1906 the word "free" was dropped from the service's name, and by 1929 improved roads had led almost all carriers to switch to motor cars. The number of post offices in the nation peaked at 76,945 in 1901 and declined steadily after that.
Answer: A
West Virginia: Correct. Paragraph 2: service began "in Charles Town, Halltown, and Uvilla, in Wilson's home state of West Virginia."
Maryland: Maryland is not mentioned in the passage.
Virginia: Near-miss name: the passage says West Virginia, not Virginia.
Georgia: No Georgia towns are named in the passage; the first routes were elsewhere.
Read names exactly; a near-miss place name is a common detail trap.
1Many of the world's caves were not dug by animals or blasted by people. They were dissolved. These solution caves form mainly in limestone, though they also form in marble, dolomite, gypsum and halite, or rock salt. Water works its way along joints (fractures), faults and layers in the rock, slowly dissolving it and carrying it away.
2The water does this work with the help of carbonic acid, a very weak acid that forms when carbon dioxide dissolves in water. Some of the carbon dioxide comes from the air and some from the breathing of animals, but most of it is picked up as rain and melting snow soak through the soil. The slightly acidic water then seeps downward until it reaches the limestone below.
3At first, the water creeps through tiny cracks. As the cracks widen, more water can flow through them, and streams begin to carry sediment that scours the rock and enlarges the passages. Bigger streams form bigger passages. Even so, the process is extremely slow. A passage with an active stream grows by at most about 1 millimeter per year, which would make a passage about 1 meter wide in a thousand years. Many caves are hundreds of thousands to millions of years old.
4The same chemistry that hollows out a cave also decorates it. When dripping water reaches the open air of the cave, it releases carbon dioxide, much as a bottle of soda does when it is opened. The water can then no longer hold as much calcite, the mineral that makes up limestone, and the calcite is deposited again on the ceiling, walls and floor. A stalactite begins as a hollow "soda straw": as a drop hangs from the ceiling and loses carbon dioxide, a thin ring of calcite forms around its edge. Water that still carries dissolved calcite when it drips to the floor can build a stalagmite.
5These formations, called speleothems, grow at different speeds. Two important factors are the temperature outside the cave and the amount of rainfall. Warm weather speeds the decay of plants and animals, which adds carbon dioxide to the soil, and more rain carries more dissolved calcite down into the cave. Pure calcite is white, so the red, orange and black shades of many formations come from iron and other minerals.
Based on the passage, how would a long cold, dry period above a cave most likely affect the growth of its stalactites?
Answer: A
Growth would slow, with less rain and less soil carbon dioxide.: Correct. Paragraph 5 says warm weather speeds decay and adds carbon dioxide to the soil, and more rain carries more dissolved calcite into the cave; a cold, dry period reduces both, so growth slows.
Growth would stop for good, because the cave would fill with ice.: The passage says nothing about ice; it describes slower or faster growth, not a permanent stop.
Growth would not change, because caves are sealed from the surface.: Contradicts paragraphs 2 and 5: rain, soil and outside temperature all affect the water that reaches the cave.
Growth would speed up, because cold water deposits calcite faster.: Outside knowledge: the passage never says cold water deposits calcite faster.
Follow the chain the passage gives (weather → soil carbon dioxide → dissolved calcite → deposits) and change one link at a time.
1Many of the world's caves were not dug by animals or blasted by people. They were dissolved. These solution caves form mainly in limestone, though they also form in marble, dolomite, gypsum and halite, or rock salt. Water works its way along joints (fractures), faults and layers in the rock, slowly dissolving it and carrying it away.
2The water does this work with the help of carbonic acid, a very weak acid that forms when carbon dioxide dissolves in water. Some of the carbon dioxide comes from the air and some from the breathing of animals, but most of it is picked up as rain and melting snow soak through the soil. The slightly acidic water then seeps downward until it reaches the limestone below.
3At first, the water creeps through tiny cracks. As the cracks widen, more water can flow through them, and streams begin to carry sediment that scours the rock and enlarges the passages. Bigger streams form bigger passages. Even so, the process is extremely slow. A passage with an active stream grows by at most about 1 millimeter per year, which would make a passage about 1 meter wide in a thousand years. Many caves are hundreds of thousands to millions of years old.
4The same chemistry that hollows out a cave also decorates it. When dripping water reaches the open air of the cave, it releases carbon dioxide, much as a bottle of soda does when it is opened. The water can then no longer hold as much calcite, the mineral that makes up limestone, and the calcite is deposited again on the ceiling, walls and floor. A stalactite begins as a hollow "soda straw": as a drop hangs from the ceiling and loses carbon dioxide, a thin ring of calcite forms around its edge. Water that still carries dissolved calcite when it drips to the floor can build a stalagmite.
5These formations, called speleothems, grow at different speeds. Two important factors are the temperature outside the cave and the amount of rainfall. Warm weather speeds the decay of plants and animals, which adds carbon dioxide to the soil, and more rain carries more dissolved calcite down into the cave. Pure calcite is white, so the red, orange and black shades of many formations come from iron and other minerals.
Which of the following statements about solution caves is true, based on the passage?
Answer: B
Solution caves form only in limestone and in no other rock.: Added qualifier: paragraph 1 also lists marble, dolomite, gypsum and halite.
Most of the carbon dioxide in cave-forming water comes from the soil.: Correct. Paragraph 2: "most of it is picked up as rain and melting snow soak through the soil."
Stalagmites begin as hollow soda straws on the cave floor.: Detail swap: paragraph 4 says stalactites, which hang from the ceiling, begin as soda straws.
Pure calcite gives cave formations their red and orange colors.: Reversed: paragraph 5 says pure calcite is white and the colors come from iron and other minerals.
Words such as "only" and swapped pairs (stalactite/stalagmite) are the usual traps in true-statement items.
1Many of the world's caves were not dug by animals or blasted by people. They were dissolved. These solution caves form mainly in limestone, though they also form in marble, dolomite, gypsum and halite, or rock salt. Water works its way along joints (fractures), faults and layers in the rock, slowly dissolving it and carrying it away.
2The water does this work with the help of carbonic acid, a very weak acid that forms when carbon dioxide dissolves in water. Some of the carbon dioxide comes from the air and some from the breathing of animals, but most of it is picked up as rain and melting snow soak through the soil. The slightly acidic water then seeps downward until it reaches the limestone below.
3At first, the water creeps through tiny cracks. As the cracks widen, more water can flow through them, and streams begin to carry sediment that scours the rock and enlarges the passages. Bigger streams form bigger passages. Even so, the process is extremely slow. A passage with an active stream grows by at most about 1 millimeter per year, which would make a passage about 1 meter wide in a thousand years. Many caves are hundreds of thousands to millions of years old.
4The same chemistry that hollows out a cave also decorates it. When dripping water reaches the open air of the cave, it releases carbon dioxide, much as a bottle of soda does when it is opened. The water can then no longer hold as much calcite, the mineral that makes up limestone, and the calcite is deposited again on the ceiling, walls and floor. A stalactite begins as a hollow "soda straw": as a drop hangs from the ceiling and loses carbon dioxide, a thin ring of calcite forms around its edge. Water that still carries dissolved calcite when it drips to the floor can build a stalagmite.
5These formations, called speleothems, grow at different speeds. Two important factors are the temperature outside the cave and the amount of rainfall. Warm weather speeds the decay of plants and animals, which adds carbon dioxide to the soil, and more rain carries more dissolved calcite down into the cave. Pure calcite is white, so the red, orange and black shades of many formations come from iron and other minerals.
At the fastest rate the passage describes, about how long would a stream take to enlarge a passage to 3 meters wide?
Answer: C
300 years: Divided by 10 instead of multiplying: at 1 mm per year, 300 years gives only 0.3 meter.
1,000 years: This is the time for a 1-meter passage (paragraph 3), not a 3-meter one.
3,000 years: Correct. Paragraph 3: at most 1 mm per year, or about 1 meter per thousand years, so 3 meters takes about 3,000 years.
30,000 years: An extra factor of 10: 30,000 years at 1 mm per year would give 30 meters.
Scale a stated rate in proportion: if 1 meter takes 1,000 years, 3 meters takes three times as long.
According to the passage, why is calcite deposited when dripping water reaches the open air of a cave?
1Many of the world's caves were not dug by animals or blasted by people. They were dissolved. These solution caves form mainly in limestone, though they also form in marble, dolomite, gypsum and halite, or rock salt. Water works its way along joints (fractures), faults and layers in the rock, slowly dissolving it and carrying it away.
2The water does this work with the help of carbonic acid, a very weak acid that forms when carbon dioxide dissolves in water. Some of the carbon dioxide comes from the air and some from the breathing of animals, but most of it is picked up as rain and melting snow soak through the soil. The slightly acidic water then seeps downward until it reaches the limestone below.
3At first, the water creeps through tiny cracks. As the cracks widen, more water can flow through them, and streams begin to carry sediment that scours the rock and enlarges the passages. Bigger streams form bigger passages. Even so, the process is extremely slow. A passage with an active stream grows by at most about 1 millimeter per year, which would make a passage about 1 meter wide in a thousand years. Many caves are hundreds of thousands to millions of years old.
4The same chemistry that hollows out a cave also decorates it. When dripping water reaches the open air of the cave, it releases carbon dioxide, much as a bottle of soda does when it is opened. The water can then no longer hold as much calcite, the mineral that makes up limestone, and the calcite is deposited again on the ceiling, walls and floor. A stalactite begins as a hollow "soda straw": as a drop hangs from the ceiling and loses carbon dioxide, a thin ring of calcite forms around its edge. Water that still carries dissolved calcite when it drips to the floor can build a stalagmite.
5These formations, called speleothems, grow at different speeds. Two important factors are the temperature outside the cave and the amount of rainfall. Warm weather speeds the decay of plants and animals, which adds carbon dioxide to the soil, and more rain carries more dissolved calcite down into the cave. Pure calcite is white, so the red, orange and black shades of many formations come from iron and other minerals.
Answer: A
The water releases carbon dioxide into the cave air.: Correct. Paragraph 4: the water "releases carbon dioxide," so it "can then no longer hold as much calcite."
The water absorbs carbon dioxide from the cave air.: Reversed: the water gives off carbon dioxide; gaining it would make the water more acidic and better at dissolving rock.
The water picks up iron from the cave walls.: Iron explains the colors of formations (paragraph 5), not why calcite is deposited.
The water turns into ice in the cool cave air.: The passage never mentions freezing; deposition comes from the loss of carbon dioxide.
For cause questions, find the "when … then" chain in the passage and choose the option that states the first link correctly.
1A glacier begins as snow. In places where more snow falls in winter than melts in summer, the snow piles up year after year. The weight of each new layer presses on the layers beneath it. Snow that survives a full year becomes a dense, grainy material called firn, and as the pressure continues, the grains squeeze together until almost no air is left. Turning firn into solid glacier ice can take more than a century.
2Ice looks hard and brittle, yet a glacier flows. Once ice is thicker than about 30 meters, the weight of the ice above causes the deeper ice to deform slowly, much like very stiff putty. The crystals inside the ice shift and change shape, and the whole mass creeps downhill. Scientists call this process internal deformation.
3The ice near the surface behaves differently. The top layer, up to roughly 50 meters thick, is under too little pressure to flow. It stays rigid, and the ice below this brittle layer flows and carries it along. When a glacier passes over a bump in its bed or turns a bend, or when one part moves faster than another, this brittle surface cracks open, forming deep cracks called crevasses. Most crevasses are less than about 46 meters deep, because below that depth the ice bends instead of breaking.
4A glacier can also move by sliding. Water collects at the base of many glaciers, melted by pressure, by the heat of friction, or by heat from the earth. This water acts like a lubricant, letting the ice slide over the rock beneath it. Friction still slows the ice wherever it touches solid ground. The bottom of a glacier moves more slowly than its surface, and in a mountain valley the ice along the valley walls moves more slowly than the ice in the middle.
5Most glaciers move at an average of about one meter per day, too slowly to see. Some fast glaciers in Greenland travel 20 to 30 meters per day. A few glaciers also surge, speeding up for a short time to as much as about 90 meters per day.
Which of the following best states the main idea of the passage?
Answer: C
Glacier surges are the main danger to mountain towns.: The passage mentions surges only briefly and never discusses danger to towns.
Greenland has the fastest glaciers anywhere in the world.: A detail from paragraph 5, and the passage does not call them the fastest anywhere.
Glaciers move through slow flow inside the ice and by sliding.: Correct. Paragraphs 2–4 explain the two ways glaciers move: internal deformation and sliding on water at the base.
Crevasses form because glaciers are made of pure snow.: Crevasses form when the brittle top layer cracks; glaciers are made of ice, not pure snow.
The main idea covers most of the passage; a detail from a single paragraph is too narrow, even if true.
1A glacier begins as snow. In places where more snow falls in winter than melts in summer, the snow piles up year after year. The weight of each new layer presses on the layers beneath it. Snow that survives a full year becomes a dense, grainy material called firn, and as the pressure continues, the grains squeeze together until almost no air is left. Turning firn into solid glacier ice can take more than a century.
2Ice looks hard and brittle, yet a glacier flows. Once ice is thicker than about 30 meters, the weight of the ice above causes the deeper ice to deform slowly, much like very stiff putty. The crystals inside the ice shift and change shape, and the whole mass creeps downhill. Scientists call this process internal deformation.
3The ice near the surface behaves differently. The top layer, up to roughly 50 meters thick, is under too little pressure to flow. It stays rigid, and the ice below this brittle layer flows and carries it along. When a glacier passes over a bump in its bed or turns a bend, or when one part moves faster than another, this brittle surface cracks open, forming deep cracks called crevasses. Most crevasses are less than about 46 meters deep, because below that depth the ice bends instead of breaking.
4A glacier can also move by sliding. Water collects at the base of many glaciers, melted by pressure, by the heat of friction, or by heat from the earth. This water acts like a lubricant, letting the ice slide over the rock beneath it. Friction still slows the ice wherever it touches solid ground. The bottom of a glacier moves more slowly than its surface, and in a mountain valley the ice along the valley walls moves more slowly than the ice in the middle.
5Most glaciers move at an average of about one meter per day, too slowly to see. Some fast glaciers in Greenland travel 20 to 30 meters per day. A few glaciers also surge, speeding up for a short time to as much as about 90 meters per day.
Which of the following statements about glaciers is true, based on the passage?
Answer: B
Firn changes into glacier ice in a single winter.: Paragraph 1 says turning firn into ice "can take more than a century," not a single winter.
Heat from friction can melt ice at the base of a glacier.: Correct. Paragraph 4 lists water "melted by pressure, by the heat of friction, or by heat from the earth."
The surface of a glacier moves more slowly than its bottom.: Reversal: paragraph 4 says "the bottom of a glacier moves more slowly than its surface."
Crevasses usually reach all the way to the glacier's bed.: Paragraph 3 says most crevasses are less than about 46 meters deep, because deeper ice bends instead of breaking.
A single reversed word such as "slower" or "faster" makes a statement false; compare each option word by word with the passage.
1A glacier begins as snow. In places where more snow falls in winter than melts in summer, the snow piles up year after year. The weight of each new layer presses on the layers beneath it. Snow that survives a full year becomes a dense, grainy material called firn, and as the pressure continues, the grains squeeze together until almost no air is left. Turning firn into solid glacier ice can take more than a century.
2Ice looks hard and brittle, yet a glacier flows. Once ice is thicker than about 30 meters, the weight of the ice above causes the deeper ice to deform slowly, much like very stiff putty. The crystals inside the ice shift and change shape, and the whole mass creeps downhill. Scientists call this process internal deformation.
3The ice near the surface behaves differently. The top layer, up to roughly 50 meters thick, is under too little pressure to flow. It stays rigid, and the ice below this brittle layer flows and carries it along. When a glacier passes over a bump in its bed or turns a bend, or when one part moves faster than another, this brittle surface cracks open, forming deep cracks called crevasses. Most crevasses are less than about 46 meters deep, because below that depth the ice bends instead of breaking.
4A glacier can also move by sliding. Water collects at the base of many glaciers, melted by pressure, by the heat of friction, or by heat from the earth. This water acts like a lubricant, letting the ice slide over the rock beneath it. Friction still slows the ice wherever it touches solid ground. The bottom of a glacier moves more slowly than its surface, and in a mountain valley the ice along the valley walls moves more slowly than the ice in the middle.
5Most glaciers move at an average of about one meter per day, too slowly to see. Some fast glaciers in Greenland travel 20 to 30 meters per day. A few glaciers also surge, speeding up for a short time to as much as about 90 meters per day.
Scientists set stakes in a straight line across a valley glacier, from one wall to the other. A year later, the line would most likely
Answer: B
bend uphill, with the middle stakes farthest behind: Reversal: this would mean the middle moves slowest, but friction slows the edges, not the center.
bend downhill, with the middle stakes farthest ahead: Correct. Paragraph 4 says the ice "along the valley walls moves more slowly than the ice in the middle," so the center stakes travel farthest.
stay straight, with every stake moved the same distance: Paragraph 4 says different parts move at different speeds, so the line would not stay straight.
stay in place, because glaciers move too slowly to measure: Paragraph 5 says glaciers move about a meter a day: too slowly to see, but easily measured over a year.
Apply the passage's rule to the new setup: where friction is greatest (the walls), the ice moves least, so the middle pulls ahead.
According to the passage, about how thick is the rigid top layer of a glacier?
1A glacier begins as snow. In places where more snow falls in winter than melts in summer, the snow piles up year after year. The weight of each new layer presses on the layers beneath it. Snow that survives a full year becomes a dense, grainy material called firn, and as the pressure continues, the grains squeeze together until almost no air is left. Turning firn into solid glacier ice can take more than a century.
2Ice looks hard and brittle, yet a glacier flows. Once ice is thicker than about 30 meters, the weight of the ice above causes the deeper ice to deform slowly, much like very stiff putty. The crystals inside the ice shift and change shape, and the whole mass creeps downhill. Scientists call this process internal deformation.
3The ice near the surface behaves differently. The top layer, up to roughly 50 meters thick, is under too little pressure to flow. It stays rigid, and the ice below this brittle layer flows and carries it along. When a glacier passes over a bump in its bed or turns a bend, or when one part moves faster than another, this brittle surface cracks open, forming deep cracks called crevasses. Most crevasses are less than about 46 meters deep, because below that depth the ice bends instead of breaking.
4A glacier can also move by sliding. Water collects at the base of many glaciers, melted by pressure, by the heat of friction, or by heat from the earth. This water acts like a lubricant, letting the ice slide over the rock beneath it. Friction still slows the ice wherever it touches solid ground. The bottom of a glacier moves more slowly than its surface, and in a mountain valley the ice along the valley walls moves more slowly than the ice in the middle.
5Most glaciers move at an average of about one meter per day, too slowly to see. Some fast glaciers in Greenland travel 20 to 30 meters per day. A few glaciers also surge, speeding up for a short time to as much as about 90 meters per day.
Answer: C
30 meters: This is the thickness at which the deeper ice begins to flow (paragraph 2), not the thickness of the rigid layer.
46 meters: This is the depth of most crevasses, which form within the rigid layer.
50 meters: Correct. Paragraph 3 says "the top layer, up to roughly 50 meters thick," stays rigid.
90 meters: This is a surge speed in meters per day (paragraph 5), not a thickness.
When several numbers appear close together, match the unit and the thing measured to the question before choosing.
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