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Science Flashcards

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1
Q

What is the formula to find the temperature of a substance?

A

Length at temp unknown - Length at temp 0
———————————————————————- X 100%
Length at temp 100 - Length at temp 0

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2
Q

Convert 20˚K to ˚C

A

20˚K = 20-273

= -253˚C

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3
Q

How many ˚C is 0˚K?

A

-273˚C

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4
Q

What is the lowest possible temperatures where all molecules stop moving called?

A

Absolute zero

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5
Q

Convert 30˚C to K

A

30˚C = 30+ 273

= 303K

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6
Q

What are the 2 fixed points that a thermometer requires

A

Ice point and steam point

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7
Q

What does temperature measure?

A

It measures the average kinetic energy of molecules in a body

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8
Q

What is the SI unit of temperature

A

Kelvin (K)

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9
Q

What is the definition of heat?

A

Heat is the transfer of thermal energy from a region of higher temperature to a region of lower temperature. The transfer of thermal energy continues until both regions reach the same temperature, or in other words, thermal equilibrium.

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10
Q

What is law of conservation of mass?

A

The law of conservation of mass states that atoms in a body cannot be created or destroyed. They can be rearranged. Mass is conserved.

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11
Q

What is the law of conservation of energy?

A

Energy cannot be created or destroyed. It can only be converted from one form to another.

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12
Q

What is made use of for conduction?

A

Contact

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13
Q

What is made use of for convection?

A

Fluid current (Only for Gases and liquids)

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14
Q

What is made use of for radiation?

A

Electromagnetic waves (occurs in all directions)

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15
Q

What is conduction?

A

Conduction is the transfer of thermal energy through the material without obvious movement in the medium itself. During conduction, thermal energy is transferred from the hot end to the cool end of the object.

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16
Q

How does conduction work?

A

When the object is heated, the atoms in the part of the object which is getting heated gains heat and starts to vibrate faster. These atoms collide with their less energetic neighbours. Some of their energy is transferred to the neighbouring atoms, which in turn gain kinetic energy and start to vibrate faster. In this way, thermal energy is conducted through the object.

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17
Q

What are some things to keep in mind during conduction?

A
  • The transfer of thermal energy takes place until both regions of the object reaches thermal equilibrium
  • There is no net movements of the atoms during conduction (the atoms are still moving but not with flow)
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18
Q

Why does conduction take place better in metals than non-metals?

A

Conduction takes place in both vibrating atoms and free electrons, which is present in metals. When heated, the free elections gain energy and vibrate faster. These electrons are free to travel between the atoms and collide with other atoms and electrons transferring some of their energy to them. This process is much faster in free electrons than in conduction through the vibration of atoms in mon-metals. Thus, conduction in metals is more efficient than in non-metals, which have no free electrons.

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19
Q

What is thermal conductivity?

A

It is the rate of the transfer of thermal energy via conduction.

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20
Q

Good conductors of thermal energy?

A

Solid metals

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21
Q

Increasing conductors of thermal energy? (Top half)

A

Non metal Liquids

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22
Q

Why are non-metal liquids a better conductor then non metal solids?

A

(better than non metal solids cuz they dont have air pockets)

23
Q

Poorest conductors of thermal energy?

A

Gases (basically air, like oxygen and carbon dioxide)

24
Q

Why are solids better conductors of thermal energy than liquids and gases?

A

Their particles in a solid are closer together than liquids and gases.

25
Q

Why is are things a like wool poor conductors?

A

It has pockets of air, and since air is a poor conductor of heat since its particles are spaced far apart, reducing the collision between particles for the transfer to thermal energy, it is a poor insulator, since air is trapped inside it.

26
Q

What is a poor conductor of thermal energy called?

A

An insulator

27
Q

Two overlapping thin blankets are warmer than one thick

blanket. Explain why.

A

There will be lesser pockets exposed when a blankets are overlapping, thus the blankets help to trap
more thermal energy faster causing us to lose heat slower and feel warmer.

28
Q

In general, which state of matter do you think is the best

conductor? Suggest reasons why.

A

Liquids are the best conductors. Some solids are good conductors while others are worse than liquids. Gases are the poorest conductors of heat and thus, since liquids remain the same no no matter what material they’re made up of,
they are the best conductors of heat.

29
Q

What is the circulation of liquid called?

A

A convection current

30
Q

What happens when part of a liquid is heated?

A

When part of a liquid is heated, it gains heat and expands in volume, becoming less dense as compared to the surrounding liquid and moves upwards. Cooler and denser liquid moves downwards to replace it. The cooler liquid in turn gets heated up and rises, resulting in a continuous convection current. (REMEMBER TO RELATE TO DENSITY)

31
Q

What happens when water is heated?

A

When water is heated, the particles vibrate faster and spread further apart. The volume (space it takes up) increases and the thus the density of the water decreases. The less dense hot water rises, while the denser cold water sinks. The movement of water forms a convection current.

32
Q

What is convection? Why cant it take place in solids

A

It is the process by which thermal energy is transmitted from one place to another by the movement of heated gas or liquid. During convection, atoms need to move from one place to another, therefore convection cannot take place in solids. Convection only occurs in fluids.

33
Q

How does convection take place in gas?

A

When a gas is heated, the particles in it gain thermal energy and start to vibrate faster and spread further apart, causing its volume to increase and its density to decrease. The less dense warmer air rises upwards while the denser cooler air sinks downwards, forming a convection current. This allows the air to transfer heat from one place to another.

34
Q

How does an AC work?

A

Cold air is blown out of the AC, which sinks since it is denser than the surrounding air. The sinking of the cold air displaces the warm air, which rises and gets drawn into the AC, where it is cooled. The air is then blown out, creating a convection current.

35
Q

How does a heater help in convection?

A

The heater is placed as low as possible. Cold air at the bottom is heated up, causing it to rise, which causes the warm air on top to be displaced and sink downwards, forming a convection current, which carries heat to all parts of the room.

36
Q

How does convection occur in sea breezes?

A
  • Land’s surface heats up faster than the water surface
  • Air above land is warmer than land above sea
  • Warm air above land rises
  • cool air above sea moves inland over the lands surface gets heated up, and rises, forming a convection current.

-At night convection current forms in the opposite direction.

37
Q

If there is a fire and smoke enters a room, you should keep
your body low to the floor or crawl
to safety. Why should you do this?

A

Warmer particles like smoke would have a lower density than air and thus it would rise, and by keeping low, we prevent ourselves from inhaling the smoke, which is at the top and not found near the floor. Staying down allows us to breathe the cool air and a reduced amount of smoke. This is especially important since inhaling smoke causes choking and suffocation.

38
Q

What is the melting point of mercury?

A

-39˚C

39
Q

What is so special about mercury?

A

Mercury is the only metal that is a liquid at room temperature

40
Q

How does convection in a refrigerator work?

A

The freezer compartment will always get cold air The air around the freezer (in the fridge) will lose heat, become denser and sink to the bottom of the refrigerator and cool the food in the refrigerator. The warm less dense air in the refrigarator will rise to the top near the freezer compartment and will lose heat to the freezer compartment and becomes more dense and sinks to the bottom of the refrigerator. The cycle repeats, causing a convection current.

41
Q

What is radiation?

A

Radiation is the transfer of thermal energy through electromagnetic waves

42
Q

How does energy reach us from the sun?

A

Radiation is the reason for this. There is a vacuum between the Earth and the sun and so conduction and convection cannot take place. Only radiation can do so because it is the only means of thermal energy transmission that can take place in a vacuum.

43
Q

What is the importance of the waves in radiation?

A

The waves are known as infrared radiation. When absorbed, the energy from the infrared radiation transforms into thermal energy of the object. We can emit and absorb radiation.

44
Q

What does radiation depend on?

A 
Surface Area (greater the surface area, more radiation)
Surface Colour and texture (Black and rough, good absorber and emitter of radiation)
Surface temperature (Greater SA, more radiation)

The nature of the surface:
- The darker or rougher the surface, the more heat gained or lost per second.
The surface area:
- The greater the surface area of a body, the more heat gained or lost per second.
The temperature of the body:
- The greater the temperature difference between the body and its surroundings, the more heat gained or lost per second.

45
Q

Remember, good emitter of infrared radiation is a

A

Good absorber of thermal energy and vice versa

46
Q

Shiny surface

A

Is a good reflector of infrared radiation

47
Q

Why do birds fluff u their feathers?

A

This helps them trap air between their feathers. Since air is a poor conductor of heat, this action allows for lesser thermal energy to be lost via conduction, keeping the bird warm.

48
Q

Why does only radiation work in vacuums?

A

Conduction requires the collision of particles to transfer thermal energy while convection requires the movement of particles into open spaces for the transfer of thermal energy, however radiation makes use of electromagnetic waves to emit and absorb infrared radiation and thus it works in a vacuum.

49
Q

Name all the diatomic elements

A

Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine, Bromine, Iodine

50
Q

What is the name of group 17 elements and what is special abt them?

A

Halogens and they are reactive

51
Q

Group 18 and specialty?

A

Noble gases, unreactive

52
Q

Group 1

A

Alkali, reactive

53
Q

Group 2

A

Alkaline earth metal, reactive

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