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Science Basics | Waves, Matter, Living Things and Strata, Set 2

1 / 100.0s

Problem 1

Comparing two sound waveforms recorded over the same length of time, waveform B vibrates twice as many times as waveform A. Their amplitudes are the same.

Judging from basic relationships, how do the two sounds compare in pitch and loudness?

View explanation

B vibrates more times in the same period, so its frequency is higher and it is the higher sound. Amplitude, which relates to loudness, is equal, so on a basic comparison of waveforms they are equally loud. The point is not to treat frequency and amplitude as the same property.

Problem 2

The same person walks on soft snow, first in ordinary shoes and then wearing snow walking gear broader than the soles. The weight of the gear can be ignored.

Why does the broader gear make you sink into the snow less?

View explanation

If the force pressing on a surface is the same, spreading it over a larger contact area reduces the force per unit area — the pressure. The snow is therefore less likely to be pushed in locally. Widening the contact area does not make gravity or the person's weight disappear.

Problem 3

A galvanometer is connected to a coil. Bringing the north pole of a bar magnet toward the coil swings the needle right. Holding the magnet still inside the coil returns the needle to center, and then moving the north pole away swings the needle left.

Which explains this result correctly?

View explanation

An induced current arises when the coil and magnet move relative to one another, so holding the magnet still returns the galvanometer to center. And because the needle swung the opposite way when approaching and receding, reversing the direction of motion reverses the direction of the induced current.

Problem 4

Gas collected from carbonated water is tested with suitable safety equipment: limewater turns cloudy white, and a burning joss stick goes out in the gas.

Which gas fits both results?

View explanation

Carbon dioxide turns limewater cloudy white and does not sustain burning, so the stick goes out. Oxygen supports combustion, so you would expect the stick to burn more brightly. Combining the extinguished flame with the cloudy limewater is what identifies the gas.

Problem 5

For a substance whose solubility in water falls as the temperature drops, a saturated solution is made hot and then cooled gently, and crystals appear. Evaporation of water can be ignored.

Which best explains why the crystals appeared?

View explanation

The limit of what dissolves in water falls for this substance as the temperature drops, so some of the solute dissolved when hot can no longer stay in solution after cooling and appears as crystals. No new solute is created; what was already in the solution is recovered.

Problem 6

A starch solution is divided in two. A solution containing amylase is added to A and the same volume of water to B, and both are left at the same temperature for a fixed time. The results were: - A: no blue-purple color with iodine solution; positive for sugar - B: blue-purple with iodine solution; negative for sugar

Which conclusion is best supported by comparing A and B?

View explanation

In A the blue-purple indicating starch did not appear and the test for sugar did. In B, without amylase, starch remained and no sugar was detected, so the difference supports amylase having broken the starch down. The blue-purple of iodine solution indicates starch, not sugar.

Problem 7

Organic matter in forest leaf litter decreases through the action of fungi and bacteria, after which inorganic matter that plants can take up through their roots increases in the soil.

What role do these fungi and bacteria play in the ecosystem?

View explanation

Decomposers such as fungi and bacteria break down the organic matter in remains and waste into inorganic matter. Plants then use that inorganic matter, so materials cycle within the ecosystem. The point is that leaf litter is not simply made to vanish but returned to the cycle in another form.

Problem 8

Two comparable branches cut from the same plant have their cut ends placed in water. Branch A keeps its leaves and branch B has them removed, and each is covered with a transparent bag. After a while more droplets have formed in A's bag than in B's.

Which is the main reason for the difference?

View explanation

Some of the water a plant draws up is released as vapor, mainly through the stomata of the leaves. That transpired vapor cools on the inside of the bag and forms droplets, which is why more were seen with the leaves of A. The droplets are not liquid water newly created and expelled by the leaves.

Problem 9

Seen from Earth, the Sun and the Moon lie in roughly opposite directions in the sky. Assume no lunar eclipse is occurring.

Which shape of the Moon seen from Earth does this most nearly correspond to?

View explanation

When the Sun and Moon are roughly 180 degrees apart as seen from Earth, the sunlit face of the Moon is turned toward us, so it appears full. A new moon occurs when the Moon and Sun lie in roughly the same direction, the opposite arrangement.

Problem 10

Columnar sections from points A and B, 2 km apart, are compared. Both have a thin volcanic ash layer with the same distinctive mineral composition and color, and the order of the strata above and below matches. The present elevation of that ash layer differs between A and B, however.

Which is the most appropriate correlation of strata to draw from this evidence?

View explanation

Strata at separate points are correlated using several clues: the size, shape and color of the constituent grains, distinctive volcanic ash, and the order of superposition. Even if present elevations differ, a match in the mineral composition and color of the ash and in the order above and below raises the possibility of corresponding layers from the same eruption. The important thing is not to conclude from elevation or thickness alone.