ch14 COPY Flashcards

1
Q

how do you get impulse from a force time graph

A

the area under a force-time graph is equal to the impulse

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2
Q

motion of gas particles how do gas particles exert pressure

A

gas particles are in constant random brownian motion,

They continuously collide with each other and the walls of their container, causing a change in momentum (impulse) producing a force

this force results in pressure (p = F / A), which exerts a pressure on the containers

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3
Q

describe the pathing of gas particles

A

particles take a random path, they don’t travel in a straight line because they’re constantly changing direction due to collisions

displacement is proportional to the square root of number of steps

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4
Q

what is boyle’s law

A

provided that temp and amount of gas remains constant, pressure is inversely proportional to the volume

pV = constant

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5
Q

practical to look at boyle’s law

A

set up as shown, must have a trapped volume of gas whose pressure can be changed and whose volume measured

increasing pressure forces oil into the calibrated tube, while decreasing allows oil out the tube

by keeping temp constant, you can investigate the variation in volume with pressure

uncertainties: tube might fracture

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6
Q

relationship between pressure and number of molecules

A

provided that the volume is kept constant

the number of molecules is directly proportional to the pressure

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7
Q

how to work out number of molecules N

A

number of molecules N = moles n * avagadro constant Na

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8
Q

what is an ideal gas

A

a model for a gas where the particles are assumed to have negligible volume, there are negligible forces between particles except during collisiosn and the collisions are perfectly elastic,

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9
Q

what is charle’s law

A

at constant pressure, volume is directly proportional to absolue temperature T

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10
Q

what is the pressure law:

A

at constant volume, pressure is directly proportional to absolute temperature T

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11
Q

how to go from degrees to kelvin

A

kelvin = degrees celsius + 273

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12
Q

how to determine absolute 0

A

set up apparatus as shown

measure length L of the air column at different temperatures to see how the volume of enclosed gas is changing

you can mount the tube in a tall glass beaker of water whose temp can be changed

you must however be careful to ensure temp in water is similar to the temp in the enclosed air of the capillary tube

the data obtained can be used to find absolute temperature

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13
Q

ideal gas equations

A

pV = nRT

pV = NkT

p = pressure

v = volume

n = number of moles

N = number of molecules

R = gas constant

k = boltzmann constant

T = temperature (kelvin)

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14
Q

ideal gas law (molecules in a box)

what is the c² representing

A

pV = 1/3Nmc²

c² is for the mean squared

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15
Q

how to get value of molecular speeds

A

the value of molecular speeds is the square root of the mean square speed

this is the root mean square speed

RMS

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16
Q

combine pv = Nkt and pv = 1/3Nmc²

what does the result mean

A

NkT = 1/3Nmc²

NkT = 2/3N(1/2mc²)

3/2KT = 1/2 mc²

that for a certain temp, all molecukes of gases in a mixture of gases have the same kinetic energy

17
Q

what is mean free path

how to use this to calculate displacement of a molecule

A

distance between collisions

displacement = square root of steps

displacement = distance travelled / mean free path

number of steps N = (distance travelled / mean free path)²

so displacement = N * mean free path

18
Q

what can energy transfer lead to

A

a change in temperature

19
Q

how to calculate change in internal energy U

A

change in U (internal energy) = W + Q

w = work done

q = heat it receives

20
Q

what is specific thermal capacity

A

the increase in internal energy required to raise the temp of 1kg of a substance by 1K

21
Q

equation to calculate change in internal energy with c

A

Q (ΔU) = mcΔT

22
Q

how to determine Specific thermal capacity

A

set up as shown

you can find out work done by heater from appropriate readings

increase temp by about 10K, attach ammeter and voltmeter to calculate work done from W = VIT

warning: must minimise Q, the energy transferred thermally into or out the substance so that work done W = ΔU from which you can calc c

23
Q

Why is the value you get for specific thermal capacity usually too high in experiments? How can you improve this?

A

Some of the energy from the heater will get transferred to the air and the container. To minimise this affect, start below and finish above room temperature to cancel out gains and losses. Some energy will also be lost due to resistance in the circuit

24
Q

What equation do you get if you combine all three gas laws?

A

pV/T = constant

25
Q

What does the graph of pressure against temperature look like for an ideal gas?

A

A straight line, intersecting the X axis at -273.15 Celsius, with a positive gradient

26
Q

Explain why the volume of the box is inversely proportional to the pressure

A

Imagine you shrink the box. The particles have less distance to travel before they hit a wall, so you’ve increased the number of times the particles hit the walls of the box per second, which increases the total force on the wall. Because the box is now smaller, the area of the wall is smaller. So there is a greater force on a smaller area, meaning the pressure is greater

27
Q

Explain why the pressure will be greater in a box, if the particle travels faster

A

The faster the particles, the larger its momentum, so the greater the impulse of the collision and the larger the force on the wall. The particle will also take less time to travel across the box and back again, and so will hit the walls more often. And as pressure = force/area, the pressure will be greater to

28
Q

Explain root mean square speed

A

As the particles in a gas are moving in different directions, if you averaged their velocities you’d get zero
Instead, you take the average of the squared velocities. This quantity is called the mean square speed
The square root of this number gives you the speed of a typical particle, the root mean square speed

29
Q

What is Newton’s second law in relation to gas particles?

A

The force exerted by a particle in a collision is equal to the rate of change of momentum of the particle

30
Q

What does newtons second law mean about the force exerted on the wall depending on the speed of the particle?

A

If a particle collides with a wall of the container, the faster it is travelling, the more force it exerts on the wall

31
Q

relationship between rms speed and density

A

Crms ∝ 1 / (sqr root) density