Physics Test Review #3

Ceiling fans can make you feel cooler in a warm room. Do ceiling fans reduce room temperature?

No

Does the period of a pendulum depend on the mass of the bob?

No

In a glass of water at room temperature, do all the molecules have the same speed?

No

Will sound travel in a vacuum?

No, it requires a medium in which to travel.

If the Moon blew up, would we hear it?

No, space is a vacuum, and sound can't pass through a vacuum.

Wrap a fur coat around a thermometer? Will the temperature rise?

No. Fur coats insulate, which means wrapping the fur coat around a thermometer will protect it from getting warmer or colder.

Distinguish between these different aspects of a wave: period, amplitude, wavelength, and frequency.

Period is the time from one crest to the next, amplitude is the distance from the midpoint to a crest, wavelength is the distance from one crest to the next, and frequency is the number of crests that pass per second.

What is the relationship between frequency and pitch?

Pitch is the human perception of sound frequency

In which form of heat transfer is a medium not required?

Radiation

What kind of motion should you impart to a stretched coiled spring (or Slinky) to provide a longitudinal wave?

Shake it to and fro along the direction of its length, so that a series of compressions and rarefactions is produced.

What kind of motion should you impart to a stretched coiled spring (or Slinky) to provide a transverse wave?

Shake it to and fro in a direction that is perpendicular to the length of the Slinky itself

Why is the insulation in an attic commonly thicker than the insulation in the walls of a house?

Since hot air rises the cool air falls; in the winter when the house is heated the heat air will rise and the insulation will slow down the transfer of energy so the house stays warm longer. And even in the warmer days the attic will always be the warmest room because of the hot air rising.

Distinguish between temperature and heat.

Temperature is the average kinetic energy per particle. Heat is the transfer of energy due to a temperature change.

According to the law of conservation of energy, if ocean water cools, something else should warm. What is it that wars?

The air currents

According to the law of conservation of energy, if ocean water cools, then something else should warm. What is it that warms?

The cooling ocean warms the air.

What happens to the frequency of the wave if you increase the wavelength, keeping the velocity of the wave constant?

The frequency decreases.

What happens to the frequency of the wave if you increase the wave velocity, keeping the wavelength of the wave constant?

The frequency increases

What is the reason for ice being less dense than water?

The hydrogen bonding gives water a crystal structure with considerable space between the molecules, making it expand in size and become less dense in a solid state than in a liquid one.

What is evaporation, and why is it a cooling process? Exactly what is it that cools?

The more energetic liquid molecules escape into the surrounding air. Thus, the average speed of the liquid molecules decrease. The liquid temperature will then decrease.

Why can you determine wind direction by wetting your finger and holding it up in the air?

The side of your finger that feels colder is the way the wind is blowing from. This is caused by the fact that the water on your finger evaporates faster with a current of air flowing over it. As water evaporates, it takes thermal energy from the surrounding air and the surface of your finger to change from a liquid into a gas.

If the wavelength of sound is doubled, what change will occur in its speed?

The speed will double.

If the frequency of sound is doubled, what change will occur in its speed?

The speed will not change at all, but its wavelength will be "compressed" to half size. The speed of sound depends only on the medium through which it travels, not on its frequency, wavelength, or intensity.

What happens when you heat water that is at 0∘C?

The temperature increases until it reaches 100∘C.

What happens to the temperature when you heat ice that is at -40∘C?

The temperature increases until the ice reaches its melting point.

What happens to the temperature when you heat ice that is at 0∘C?

The temperature stays constant until all the ice is melted.

What happens when you heat water that is at 100∘C?

The temperature stays constant until all the water is boiled.

Why does water vapor in the air condense when the air is chilled?

The water molecules in the air move slower as the air is chilled. As a result, they coalesce.

Consider two glasses, one filled with water and the other half-full, with the water in the two glasses being at the same temperature. In which glass are the water molecules moving faster?

The water molecules in the full glass and half-full glass are moving at the same average speed.

Which of the following changes would make the water balloon more likely to pop?

Use a liquid that has a lower heat capacity than water. Use a thicker balloon.

If a vibrating guitar string is made shorter (as by holding a finger on it), how does this affect the wavelength and frequency of vibration?

Wavelength decreases and frequency increases

When you step inside a warm ski lodge on a cold day, you find your eyeglasses fog. Why does this occurs?

While outside, the lenses of your glasses had cooled to the point that when you walked inside, they were cooler than the dew point temperature of the air in the building. The water vapor in the relatively warmer, and more moist air condensed, hence fogging your glasses.

Does the period of a pendulum depend on the length of the string?

Yes

Is a steam burn more damaging than a burn from boiling water (for the same amount of liquid and vapor at the same temperature of 100 C)?

Yes. Phase changes require a lot more energy than just a temperature change. When steam (water in the gas phase) hits your skin, a lot of energy will be released as it condenses into a liquid, undergoing a phase change.

When can you add heat to something without raising its temperature?

You can add heat without changing temperature when the substance is undergoing a change of phase.

How can you double the frequency of a wave if you have control over both the wavelength and the wave velocity?

You can either halve the wavelength, keeping the wave speed constant; or double the wave speed, keeping the wavelength constant.

The molecules in a room-temperature glass of water jostle around at

a great variety of speeds.

Which has the longer period, a short or a long pendulum?

a long pendulum

A good heat conductor is

a poor insulator

Does a liquid release energy or absorb energy when it changes into a gas?

absorb energy

Objects that radiate relatively well

absorb radiation relatively well.

When a solid is changed to a liquid state, the solid

absorbs energy

When a block of ice at zero degrees Celsius melts, the ice

absorbs energy but does not change its temperature.

Energy transfer by convection is primarily restricted to

all fluids

Do the molecules in a liquid all have about the same speed, or do they have a wide variety of speeds?

all molecules in a liquid have a wide variety of speeds

The vibrations along a longitudinal wave move in a direction _______.

along and parallel to the wave

When the temperature of a strip of iron is increased, the length of the strip ___________.

also increases

Boiling is evaporation that mainly occurs _______.

below the surface and throughout water

A liter of hot water will cool to room temperature faster in a

black pot

Which body glows with electromagnetic waves?

both the Sun and the Earth

Heat energy is measured in units of

calories and/or joules

The inside surface of a glass window becomes wet when the temperature outside is

colder

A Thermos bottle controls heat transfer by _______.

conduction, convection, and radiation

Substances absorb heat energy by the process of

convection, conduction, and radiation

Aluminum has a specific heat capacity more than twice that of copper. Place equal masses of aluminum and copper wire in a flame and the one to undergo the greater increase in temperature will be

copper

When a bimetallic bar made of copper and iron strips is heated, the bar bends toward the iron strip. The reason for this is

copper expands more than iron.

If a pendulum is shortened, does its period increase or decrease?

decrease

When heat is added to boiling water, its temperature

does not change

When we speak about heat we refer to ___________.

energy that is transferred between two substances that are at different temperatures

Thermal convection applies mainly to _______.

fluids

When a sound source approaches a stationary listener, the listener experiences an increase in sound _______.

frequency

When you touch a cold piece of ice with your finger, energy flows

from your finger to the ice

Condensation is a change of phase from _______.

gas to liquid

Steam burns are more damaging than burns caused by boiling water because steam

has more energy per kilogram than boiling water, and gives up additional energy when it condenses

Food in a pressure cooker is cooked faster because of the

higher temperature

Compared to a giant iceberg, a hot cup of coffee has

higher temperature, but less internal energy.

If a pendulum is shortened, does its frequency increase or decrease?

increase

A railroad locomotive is at rest with its whistle shrieking, then starts moving toward you. Does the frequency of sound that you hear increase, decrease, or stay the same? How about the wavelength reaching your ear? How about the speed of sound in the air between you and the locomotive?

increases decreases stays the same

Warm air rises because faster-moving molecules tend to move to regions of

less density and less pressure

To say that evaporation is a cooling process is to say that the

more energetic particles escape.

If the specific heat of water were lower than it is, ponds in the cold of winter would be

more likely to freeze

Ice has a lower density than water because ice molecules are

more spread out in the solid state, forming open-structured, hexagonal crystals.

Suppose that we replace the aluminum with a mystery metal and repeat the experiment in the video. As in the video, the mass of the metal is the same as that of the water. Room temperature is about 20∘C before the start of the experiment. The water heats up to 40∘C, and the mystery metal heats up to 80∘C. Compared to that of water, the heat capacity of our mystery metal is

one-third as great.

Melting and freezing are _______.

opposite processes

The vibrations along a transverse wave move in a direction _______.

perpendicular to the wave

A good reflector of radiation is a

poor absorber of radiation

Consider a closed, sealed can of air placed on a hot stove. The contained air undergoes an increase in

pressure and temperature

A Thermos bottle has double glass walls with silver coating on the glass surfaces that face one another. The silver coating reduces the energy that is transferred by

radiation

Heat travels from the Sun to the Earth by the process of _______.

radiation

Does a liquid release energy or absorb energy when it changes into a solid?

release energy

When a gas is changed to a liquid state, the gas

releases energy

A refrigerator

removes internal energy from inside the refrigerator.

Morning dew on the grass is a result of

slow-moving water molecules sticking to one another.

If you stake out a plot of land with a steel tape on a very hot day, the actual amount of land you will have will be

smaller than measured

What are the four common phases of matter?

solid, liquid, gas, and plasma

Heat energy travels from an object with a high

temperature to an object with a lower temperature.

The white-hot sparks that strike your skin from a 4th-of-July-type sparkler don't harm you because

the energy per molecule is high, but little energy is transferred because of the few molecules in the spark

Evaporation is a cooling process because

the more energetic molecules are able to escape the liquid

A water-filled paper cup held in a flame will not catch fire. This is because

the paper cup cannot become appreciably hotter than the water it contains.

The higher the temperature of an object

the shorter the wavelengths it radiates.

The fact that a thermometer "takes its own temperature" illustrates

thermal equilibrium

The food in a refrigerator is cooled by

vaporization of the refrigerating fluid.

Red light has a longer wavelength than violet light. Which has the greater frequency?

violet light

When snow forms in clouds, the surrounding air

warms

During a very cold winter, water pipes sometimes burst. The reason for this is

water expands when freezing

The speed of a wave can be found by multiplying its frequency by its

wavelength

Suppose you walk on red-hot coals with bare feet. If bits of the coals do not stick to your feet, it would be best if your feet are

wet

A weight suspended from a spring is seen to bob up and down over a distance of 18 cm twice each second. What is its period?

0.5 second (period is 1/f)

A mosquito flaps its wings 580 vibrations per second, which produces the annoying 580-Hz buzz. Given that the speed of sound is 340 m/s, how far does the sound travel between wing beats? In other words, find the wavelength of the mosquito's sound.

0.59 m

What is the frequency, in hertz, that corresponds to each of the following periods? 0.10 sec, and 5.0 sec (T=1/f)

10 Hz, and 0.20 Hz

To increase the temperature of 50 grams of water by 2 Celsius degrees requires

100 calories

How many vibrations per second are associated with a 101.7-MHz radio wave?

101.7 million or 101.7 x 10^6 Hz

A weight suspended from a spring is seen to bob up and down over a distance of 18 cm twice each second. What is its frequency?

2.0 Hz (2 bobs a second)

At what temperature is liquid water most dense?

4 Celsius or 39 Fahrenheit

Water is most dense at ___________.

4°C

A weight suspended from a spring is seen to bob up and down over a distance of 18 cm twice each second. What is its amplitude?

9 cm (amplitude is the distance from the equilibrium position to the maximum displacement: one half the 18 cm peak to peak distance, or 18 cm)

What is an echo?

A sound wave that is caused by the reflection of sound waves from a surface back to the listener.

In a still room, smoke from a candle will sometimes rise only so far, not reaching the ceiling. Why?

Air currents depend on convection. In a still room, warm air collects at the top and cool air at the bottom; the air stratifies by temperature (because density depends on temperature). The smoke rises to the point where it has the same density as the air, and stops.

Why is an echo weaker than the original sound?

An echo is weaker than the original sound because the sound wave imparts energy to the surface from which it bounces.

The siren of a fire engine is heard in situations A, B, and C. Rank the pitch heard, from greatest to least, when the fire engine is traveling. A. toward the listener at 30 km/h. B. toward the listener at 50 km/h. C. away from the listener at 20 km/h.

B, A, C

Why can't you establish whether you are running a high temperature by touching your own forehead?

Because your hand is the same temperature as your forehead

How does the freezing point of a liquid compare with its melting point?

Both freezing point and melting point are the same for a pure substance.

In what form does radiant energy travel?

By electromagnetic radiation.

In one word, what is it that moves from source to receiver in wave motion?

Energy

If you hold one end of a piece of metal against a piece of ice, the end in your hand soon becomes cold. Does cold flow from the ice to your hand?

Energy "flows" from higher to lower temperature, from your hand to the ice. It is the energy, heat, flowing from your hand that produces the sensation of coolness. There is no flow from cold to hot; only from hot to cold.

When you touch a cold surface, does cold travel from the surface to your hand or does energy travel from your hand to the cold surface?

Energy travels from your hand to the cold surface.

What are the temperatures for freezing water on the Celsius and Fahrenheit scales? For boiling water?

Freezing: 0°C, 32°F Boiling: 100°C, 212°F

In which direction does heat flow spontaneously between hot and cold objects?

From high temperature to low temperature

Consider two glasses, one filled with water and the other half-full, with the water in the two glasses being at the same temperature. In which will more heat be required to increase the temperature by 1∘C?

Glass completely full

Consider two glasses, one filled with water and the other half-full, with the water in the two glasses being at the same temperature. In which is the internal energy greater?

Glass completely full.

What is meant when we say that a thermometer is in thermal equilibrium with another object?

Heat no longer flows between the object and thermometer when both are at the same temperature.

Why do substances expand when their temperature is increased?

Higher-temperature substances have greater molecular motion.

An old remedy for a pair of nested drinking glasses that stick together is to run water at different temperatures into the inner glass and over the surface of the outer glass. Which water should be hot, and which cold?

Inner glass should have the cold water and the outer glass should have the hot water. Since cold things contract and hot things expand the inner glass will loosen while the outer glass filled with hot water will be expanding.

Does a hot object contain internal energy or does it contain heat?

Internal energy

Does increased atmospheric pressure increase or decrease the boiling point of water? Why is this so?

It increases the boiling point. The pressure of the air opposes the pressure of the water that is trying to vaporize. When the atmospheric pressure is higher, the water has to get more energetic (hotter) to 'win'.

Why is lightning seen before thunder is heard?

Light travels much faster than sound.

What happens to the wavelength of a wave when the frequency decreases?

Lower frequency produces waves farther apart, so wavelength increases. Wavelength and frequency are inverse to each other.