Physics chapter 9

Brownian motion is observed by looking at smoke particles through a microscope.

How do the smoke particles move in Brownian motion?

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• all in the same direction

• at random

• in circles

• vibrating about fixed points

The diagram represents the molecules of a gas in a closed container of constant volume. What happens to the molecules when the gas is heated?

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• They expand.

• They hit the walls less often.

• They move further apart.

• They move more quickly.

A liquid is left in an open dish. After several days there is less liquid in the dish. Which statement explains this?

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• The least energetic molecules leave the surface and escape into the air.

• The least energetic molecules leave the surface and return.

• The most energetic molecules leave the surface and escape into the air.

• The most energetic molecules leave the surface and return.

A block of ice cream is prevented from melting by wrapping it in newspaper soaked in water. The water evaporates from the newspaper. Which molecules escape from the water and what happens to the average speed of the water molecules that remain in the newspaper?

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• the more energetic ones, decreases

• the more energetic ones, increases

• the less energetic ones, decreases

• the less energetic ones, increases

When a liquid evaporates, some molecules escape from it and its temperature changes. From where do the molecules escape and what is the effect on the temperature of the liquid?

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• all parts of the liquid, decreases

• all parts of the liquid, increases

• only the liquid surface, decreases

• only the liquid surface, increases

A sealed gas cylinder is left outside on a hot, sunny day. What happens to the average speed of the molecules and to the pressure of the gas in the cylinder as the temperature rises?

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• falls, falls

• falls, rises

• rises, falls

• rises, rises

Evaporation occurs when molecules escape from a liquid surface into the air above it. During this process the temperature of the liquid falls. Why does the temperature of the liquid fall?

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• The molecules in the vapour expand because the pressure is less.

• The molecules left in the liquid have more space to move around.

• The molecules move more slowly when they escape into the air.

• The molecules with the highest energies escape into the air

The molecules of a substance become more closely packed and move more quickly. What is happening to the substance?

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• A gas is being heated and compressed.

• A gas is being heated and is expanding.

• A liquid is boiling.

• A liquid is evaporating at room temperature.

On a warm day, a swimmer climbs out of a swimming pool into the open air and water evaporates from his skin. As the water evaporates, which molecules escape into the air first and what happens to the average speed of the remaining water molecules?

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• least energetic. decreases

• least energetic, increases

• most energetic, decreases

• most energetic, increases

Brownian motion is observed when looking at smoke particles in air using a microscope. What causes the smoke particles to move at random?

• Smoke particles are hit by air molecules.

• Smoke particles are moved by convection currents in the air.

• Smoke particles have different weights and fall at different speeds.

• Smoke particles hit the walls of the container.