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IB Physics > energy production > Flashcards

energy production Flashcards

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1
Q

energy density

A

energy per unit volume (MJ m−3)

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2
Q

specific energy

A

energy per unit mass (MJ kg−1)

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3
Q

2 mechanisms that convert heat to work

A

heat engine and turbine

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4
Q

how dyou convert mechanical to electrical energy

A

A generator consists of a coil rotating in a magnetic field (or a magnet rotating in a coil). According to Faraday’s law an emf is induced when the magnetic flux enclosed by the coil changes.

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5
Q

enrichment

A

processing of fuel to increase the amount of fissile nuclei (235U).

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6
Q

moderation

A

graphite used to slow down neutrons so they are absorbed (this does not slow the chain reaction but makes the reaction possible).

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7
Q

critical mass

A

the minimum amount of nuclear fuel needed for a chain reaction

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8
Q

meltdown

A

when the core of a reactor gets too hot and melts.

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9
Q

low level waste

A

radioactive waste produced during the processing of fuel and parts of the reactor that have become radioactive after exposure to radiation emitted by reactor.

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10
Q

high level waste

A

the spent fuel contains highly radioactive fission fragments. Needs to be kept away from humans for 100 000 years.

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11
Q

what does a solar heating panel do

A

absorbs radiation from the Sun and converts it into thermal energy.

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12
Q

what does a photovoltaic cell do

A

absorbs radiation and converts it into electrical energy.

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13
Q

what does a solar power station do

A

uses mirrors to reflect radiation to a central tower where water is boiled and used to turn a generator to generate electricity

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14
Q

oscillating water column

A

waves cause water to move up and down a column pushing air through a turbine which is connected to a generator

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15
Q

pelamis

A

cylinders connected by joints that bend when waves pass. Movement is used to pump a fluid through a turbine.

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16
Q

fossil fuels enhance greenhouse effect

A

use of fossil fuels increases the concentration of carbon dioxide in the atmosphere so more IR radiation is absorbed leading to an increase in the surface temperature

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17
Q

approx how much incident radiation is reflected off the ground?

A

30%

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18
Q

albedo

A

total scattered power (reflected) /total incident power

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19
Q

surface heat capacity (Cs) equation

A

Q/(A🔺T)

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20
Q

what is the stefan-boltzmann law and what is its use

A

P = A o T^4

used to calculate power radiated per unit area given temperature

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21
Q

emissivity

A

ratio of energy radiated by body/energy radiated by perfect black body at same temperature

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22
Q

wiens displacement law and use

A

peak displacement = 0.99289/T

used to determine the temperature of the sun from the peak in the spectrum

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23
Q

solar constant

A

the power per unit area at the earth (1400Wm^-2)

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24
Q

ultraviolet radiation interaction with atmosphere

A

absorbed by ozone layer

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25
Q

infrared radiation interaction with atmosphere

A

excites molecules of water, methane, and carbon dioxide (greenhouse gases)
after absorption energy is re-emitted in random directions

26
Q

interaction between visible light radiation and atmosphere

A

mostly passes through

27
Q

how can a wood burning stove be made more efficient

A

circulate the waste gases through a system of pipes, transferring heat energy to stones that retain the thermal energy long after the fire goes out

28
Q

katabatic winds

A

formed when a high pressure is caused by dense cold air pressing down at the top of a mountain, resulting in air flowing downhill

29
Q

the sun

A

burning ball of gas fuelled by a dense hot core where hydrogen is fused to form helium

30
Q

how tides work

A
  1. gravitational attraction between water in oceans and Moon causes water to bulge outwards on side facing moon and opposite side
  2. as Earth rotates these bulge travel around causing the two high tides
31
Q

bodies with same temperature but lower emissivity difference in radiation emitted

A

same peak wavelength but less power

32
Q

PN junction

A

slice of semiconductor where one side has been doped with impurities with holes and the other side impurities with electrons

33
Q

what’s the energy from nuclear?

A

when a large nucleus splits into 2 smaller ones, the total binding energy increases, resulting in the release of ~100MeV of energy

34
Q

fissile nuclei

A

235U

35
Q

2 causes of meltdown

A

malfunction in cooling system

leak in pressure vessel

36
Q

emissivity of a black body

A

1

37
Q

black body

A

a hypothetical body that absorbs without reflection all of the electromagnetic radiation incident on its surface

38
Q

why does the sun appear orange at sunrise and sunset

A

-the blue bit of the spectrum has been absorbed by the atmosphere because sunrise and sunset are further away so there’s more atmosphere to go through

39
Q

why is it not possible to get all the energy from the nuclear fuel

A

when the amount of 235U falls below a certain value a chain reaction can no longer be sustained

40
Q

control rods

A

used to slow down the reaction if it goes too fast

made of neutron-absorbing material eg Boron

41
Q

why in theory would painting surfaces white decrease the greenhouse effect?

A

if more light is reflected from the earth then less energy is absorbed, so temperature will be less

42
Q

renewable energy source

A

one where the use/depletion of energy source is less than the rate of production/regeneration of source

43
Q

how does anti-reflective layer in photovoltaic cell work?

A

light reflecting off top layer of very thin film undergoes a phase change of pi whereas light reflected off the bottom layer doesn’t. The reflected light therefore interferes destructively reducing energy loss.

44
Q

fuel

A

chemicals that when burnt release energy in the form of heat

45
Q

what changes the solar constant?

A

1) how much energy the sun is giving out (more sunspots means more energy)
2) distance between earth and sun (orbit elliptical so orbital radius changes)

46
Q

what makes materials different colours

A

whether a particular wavelength photon is absorbed or reflected by the material

47
Q

what makes smth red

A

reflects red photons but absorbs other colours

48
Q

why are black bodies black

A

cos they absorb everything they don’t reflect any photons

49
Q

average surface heat capacity of earth (not in data booklet)

A

4x10^8Jm^-2K^-1

50
Q

why does steam being released onto the blades of the turbine cause it to rotate

A

the change in momentum of the molecules will result in a force on the surface

51
Q

what is a generator and how does it work

A

a generator consists of a coil of wire in a changing magnetic field.
The changing magnetic field creates an emf in the coil, causing a current to flow in the load resistor

52
Q

energy change in generator

A

mechanical to electrical

53
Q

how does the anti-reflective layer of a photovoltaic cell reduce energy loss

A

Light reflecting off the top layer of this v. thin film undergoes a phase change of pi whereas the light reflected off the bottom layer does not
-> the light therefore interferes destructively, reducing energy loss

54
Q

stefan-boltzmann law in words

A

power per unit area is proportional to the temperature^4

55
Q

4 reasons why most of the world’s energy consumption is provided by fossil fuels

A

1) wide availability
2) ease of transportation
3) power stations can be built close to the source
4) high energy density

56
Q

energy density

A

The energy that can be liberated per kg

57
Q

what is the effect on the emission spectrum of increasing the temperature of a back body?

A

> total power radiated increases

> peak wavelength of radiation decreases

58
Q

3 markscheme points re moderator

A

1) neutrons have to be slowed down (before next fission);
2) because the probability of fission is (much) greater (with neutrons of thermal energy);
3) neutrons collide with/transfer energy to atoms/molecules (of the moderator);

59
Q

trillion standard form

A

10^13

60
Q

surface area of earth

A

5.1x10^15

61
Q

surface heat capacity

A

heat energy needed to raise 1m^2 of SA of a planet by 1*C

IB Physics (10 decks)

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