ASVAB — All Questions

At sea level, water boils at approximately what Fahrenheit temperature?

• a.180 degrees
• b.273 degrees
• c.100 degrees
• d.212 degrees✓

Water boils at 212 degrees Fahrenheit, which is 100 degrees Celsius. The figure 273 belongs to the Kelvin scale, where 273 K is the freezing point.

Which planet orbits closest to the sun?

• a.Jupiter
• b.Neptune
• c.Venus
• d.Mercury✓

Mercury holds the innermost orbit, with Venus next and Jupiter and Neptune far beyond Earth. Venus is the hotter planet even though it orbits farther out.

Which gas do plants take in from the air during photosynthesis?

• a.free oxygen gas
• b.nitrogen gas
• c.carbon dioxide✓
• d.hydrogen

Photosynthesis uses carbon dioxide and water to build sugar, releasing oxygen as a by-product. Plants take oxygen in for respiration, not for photosynthesis.

Which element makes up the greatest share of the Earth's crust by mass?

• a.oxygen✓
• b.silicon
• c.aluminum
• d.iron

Oxygen accounts for roughly 46 percent of the crust by mass, bound up in silicate and oxide minerals. Silicon is second at about 28 percent.

How many chromosomes are found in a normal human body cell?

• a.46✓
• b.64
• c.32
• d.23

A body cell holds 23 pairs, or 46 chromosomes. A sperm or egg cell carries half that number, 23.

Which of these animals is a vertebrate?

• a.earthworm
• b.frog✓
• c.jellyfish
• d.octopus

A vertebrate has a backbone, and a frog does. Earthworms, jellyfish, and octopuses have no internal skeleton of bone or cartilage.

Frequency is measured in which unit?

• a.hertz✓
• b.newtons
• c.watts
• d.joules

One hertz is one cycle per second. Newtons measure force, joules measure energy, and watts measure power.

About how fast does sound travel through air at room temperature?

• a.110,000 feet per second
• b.110 feet per second
• c.11,000 feet per second
• d.1,100 feet per second✓

Sound moves through air at roughly 1,100 feet per second, or about 760 miles per hour. That is why thunder lags several seconds behind the lightning flash.

Which of the following is a chemical change rather than a physical change?

• a.a rock being crushed
• b.iron rusting✓
• c.water boiling
• d.ice melting

Rusting produces a new substance, iron oxide, so it is a chemical change. Melting, boiling, and crushing change form or state without changing the substance.

A trait that appears only when an individual inherits two copies of the gene is described as

• a.environmental
• b.recessive✓
• c.acquired
• d.dominant

A recessive trait is masked whenever a dominant copy is present, so it shows only when both copies are recessive.

What causes the phases of the moon?

• a.its position relative to Earth and the sun✓
• b.changes in the moon's own brightness
• c.clouds in the Earth's own atmosphere
• d.the shadow of the Earth as it falls on it

Half the moon is lit at all times, and the phase is simply how much of that lit half faces Earth. The Earth's shadow causes a lunar eclipse, which is a separate event.

Nearly all of the Earth's weather occurs in which layer of the atmosphere?

• a.the thermosphere
• b.the stratosphere
• c.the troposphere✓
• d.the mesosphere

The troposphere is the lowest layer and holds most of the atmosphere's water vapor, so clouds and storms form there. The ozone layer sits above it in the stratosphere.

Through which of the following can sound not travel?

• a.liquid water
• b.humid air
• c.a vacuum✓
• d.solid steel

Sound is a pressure wave and needs particles to carry it, so it cannot cross a vacuum. It actually travels faster in water and steel than in air.

Which vitamin does the body make in skin exposed to sunlight?

• a.vitamin C
• b.vitamin K
• c.vitamin A
• d.vitamin D✓

Ultraviolet light converts a compound in the skin into vitamin D, which the body needs to absorb calcium.

What is the pH of a neutral solution?

• a.10
• b.7✓
• c.0
• d.14

On the 0 to 14 pH scale, 7 is neutral. Values below 7 are acidic and values above 7 are basic.

An animal that holds its body temperature steady regardless of its surroundings is called

• a.warm-blooded✓
• b.cold-blooded
• c.nocturnal
• d.invertebrate

Warm-blooded animals such as mammals and birds generate and regulate their own heat. Cold-blooded animals take on the temperature of their surroundings.

Which organ produces insulin?

• a.the pancreas✓
• b.the liver
• c.the kidneys
• d.the gall bladder

Cells in the pancreas release insulin, which lets the body's cells take up glucose from the blood.

Igneous rock is formed from

• a.cooled magma✓
• b.layers of compressed sediment
• c.existing rock under heat and pressure
• d.minerals left by evaporating water

Igneous rock solidifies from molten rock. Compressed sediment forms sedimentary rock, and heat and pressure on existing rock form metamorphic rock.

What force holds a satellite in orbit around the Earth?

• a.friction
• b.gravity✓
• c.magnetism
• d.air pressure

Gravity continuously pulls the satellite toward Earth while its forward motion carries it past, and the combination is an orbit.

What is the largest artery in the human body?

• a.the femoral
• b.the vena cava
• c.the carotid
• d.the aorta✓

The aorta leaves the left side of the heart and supplies every other artery. The vena cava is the body's largest vein, not an artery.

A solar eclipse occurs when

• a.the Earth passes between the moon and the sun
• b.the moon moves into the Earth's own shadow
• c.the moon passes between the Earth and the sun✓
• d.the sun passes behind the far side of Earth

In a solar eclipse the moon blocks the sun from part of the Earth's surface. When the moon moves into Earth's shadow instead, the result is a lunar eclipse.

Which of the following is a chemical element?

• a.bronze
• b.air
• c.helium✓
• d.water

Helium appears on the periodic table as a single kind of atom. Bronze is an alloy, water is a compound, and air is a mixture of gases.

In the human lung, gas exchange with the blood takes place in the

• a.diaphragm
• b.trachea
• c.alveoli✓
• d.bronchi

The alveoli are the tiny air sacs at the ends of the airways, where oxygen and carbon dioxide cross into and out of the blood. The bronchi and trachea only carry air.

The process by which water moves from a plant's leaves into the air is called

• a.germination
• b.precipitation
• c.condensation
• d.transpiration✓

Transpiration is evaporation through the pores of a leaf, and it pulls water upward from the roots. Condensation and precipitation are stages of the weather cycle.

On the Celsius scale, at what temperature does fresh water freeze?

• a.0 degrees✓
• b.32 degrees
• c.273 degrees
• d.100 degrees

Water freezes at 0 degrees Celsius, which is the same temperature as 32 degrees Fahrenheit.

A stretched spring holds which kind of energy?

• a.kinetic
• b.potential✓
• c.thermal
• d.electrical

Energy stored by position or deformation is potential energy. It becomes kinetic energy of motion when the spring is released.

A 12-volt source is connected across a 4-ohm resistor. How much current flows?

• a.48 amperes
• b.3 amperes✓
• c.8 amperes
• d.0.33 ampere

Ohm's law gives current as voltage divided by resistance: 12 / 4 = 3 amperes. Multiplying instead of dividing would give the 48 in one of the wrong choices.

Electrical resistance is measured in which unit?

• a.ohms✓
• b.watts
• c.volts
• d.amperes

Resistance is measured in ohms. Volts measure potential difference, amperes measure current, and watts measure power.

Three resistors are wired in series. How does the current through the second resistor compare with the current through the first?

• a.it is one-third as large
• b.it is the same✓
• c.it is three times as large
• d.it is twice as large

A series circuit offers only one path, so the same current passes through every element. It is the voltage that divides among series resistors.

What is the total resistance of two 6-ohm resistors connected in parallel?

• a.12 ohms
• b.3 ohms✓
• c.36 ohms
• d.6 ohms

Two equal resistors in parallel give half the resistance of one, so 6 / 2 = 3 ohms. Parallel resistance is always less than the smallest branch.

What is the total resistance of a 4-ohm and an 8-ohm resistor connected in series?

• a.4 ohms
• b.32 ohms
• c.2.67 ohms
• d.12 ohms✓

Series resistances add directly: 4 + 8 = 12 ohms. The 2.67 figure would be the result if they were in parallel.

A device draws 5 amperes from a 120-volt supply. How much power does it use?

• a.24 watts
• b.1,200 watts
• c.600 watts✓
• d.125 watts

Power equals voltage times current: 120 x 5 = 600 watts.

Which of these materials is the best conductor of electricity?

• a.rubber
• b.copper✓
• c.dry wood
• d.window glass

Copper has many free electrons and is used for most wiring. Rubber, wood, and glass are insulators.

How does a fuse protect a circuit?

• a.a metal strip melts and opens the circuit✓
• b.a coil stores the excess current safely
• c.a switch closes to divert the current
• d.a resistor absorbs the extra voltage

Excess current heats the fuse element until it melts, breaking the circuit. A fuse can only open a circuit; it cannot store or absorb current.

What is the main function of a transformer?

• a.to measure circuit current
• b.to convert AC into DC
• c.to store electrical charge
• d.to raise or lower AC voltage✓

A transformer couples two coils magnetically to change voltage. It needs a changing current, so it does not work on steady DC, and converting AC to DC is the job of a rectifier.

What does a diode do in a circuit?

• a.it increases the voltage across a load
• b.it converts current into magnetism
• c.it stores charge between its two plates
• d.it passes current in one direction only✓

A diode conducts when forward biased and blocks when reverse biased, which is why diodes are used to rectify alternating current.

A capacitor stores energy in

• a.a mechanical spring
• b.a magnetic field
• c.a chemical reaction
• d.an electric field✓

Charge collects on the capacitor's plates and the energy resides in the electric field between them. An inductor stores energy in a magnetic field instead.

What is the frequency of standard household alternating current in the United States?

• a.50 hertz
• b.120 hertz
• c.60 hertz✓
• d.110 hertz

United States utilities supply 60 hertz. Much of Europe and Asia uses 50 hertz instead.

What is the nominal voltage of a standard household outlet in the United States?

• a.12 volts
• b.120 volts✓
• c.480 volts
• d.24 volts

Ordinary branch circuits supply about 120 volts. Large appliances such as electric ranges use a 240-volt circuit.

In United States residential wiring, which insulation color identifies the equipment grounding conductor?

• a.black
• b.green✓
• c.red
• d.white

Grounding conductors are green, green with a yellow stripe, or bare copper. White marks the grounded neutral, and black and red mark ungrounded hot conductors.

Four lamps are wired in parallel across a supply. If one lamp burns out, what happens to the others?

• a.they all go dark
• b.they keep burning✓
• c.they burn much brighter
• d.they burn much dimmer

Each branch of a parallel circuit has its own path to the source, so an open branch does not interrupt the others. In a series string, one failure would darken them all.

Which change would increase the resistance of a length of copper wire?

• a.making the wire thicker
• b.making the wire longer✓
• c.cooling the wire down
• d.coiling the wire loosely

Resistance rises with length and falls as cross-sectional area increases. Cooling a metal conductor also lowers its resistance.

How is an ammeter connected in order to read the current in a circuit?

• a.across the supply terminals
• b.in parallel with the load
• c.between the load and ground
• d.in series with the load✓

The current to be measured has to pass through the ammeter, so it goes in series. An ammeter placed in parallel presents a near short circuit.

How is a voltmeter connected in order to read the voltage across a component?

• a.in parallel with the component✓
• b.in series with the component
• c.in series with the supply
• d.between the two supply fuses

Voltage is a difference between two points, so the meter bridges those two points in parallel. A voltmeter has very high resistance so it draws almost no current.

Which material is the basis of most modern semiconductor devices?

• a.aluminum
• b.silicon✓
• c.rubber
• d.copper

Silicon conducts far better than an insulator and far worse than a metal, and doping it controls that conduction precisely.

A circuit carries 2 amperes when 24 volts is applied. What is its resistance?

• a.12 ohms✓
• b.2 ohms
• c.48 ohms
• d.26 ohms

Resistance equals voltage divided by current: 24 / 2 = 12 ohms.

What is the main purpose of a resistor in a circuit?

• a.to boost voltage
• b.to rectify current
• c.to store charge
• d.to limit current✓

A resistor opposes current flow, which sets the current in a branch and divides voltage. Storing charge is a capacitor's job.

Electrical power is measured in which unit?

• a.ohms
• b.amperes
• c.watts✓
• d.coulombs

One watt is one joule per second. Ohms measure resistance, coulombs measure charge, and amperes measure current.

A step-down transformer has which winding arrangement?

• a.equal turns on both windings
• b.more turns on the secondary
• c.no winding on the secondary
• d.fewer turns on the secondary✓

Output voltage follows the turns ratio, so fewer secondary turns give a lower output voltage and a proportionally higher output current.

Two 1.5-volt cells are connected in series. What is the voltage across the pair?

• a.0.75 volt
• b.3.0 volts✓
• c.4.5 volts
• d.1.5 volts

Cells in series add their voltages: 1.5 + 1.5 = 3.0 volts. Connecting them in parallel would keep the voltage at 1.5 while doubling the available current.