Physics SME

        Key Unit Competence: 
      Evaluate the environmental survey conducted on climate change
      and greenhouse effect.

       Introductory activity
  
                    
                    Most of the solar radiation that is incident onto the Earth is absorbed and the 
                    rest is reflected into the atmosphere. Our Earth acts almost as a black body, 
                    thereby radiating back to the space part of the energy it has absorbed from the 
                   sun. The earth and its atmosphere are a part of the solar system. Life on the 

                   Earth cannot exist without the energy from the sun.

a. Basing on Physics concepts, how do humans and plants get energy from 
    the sun? Account for the use of this energy.
b. Do humans and plants maintain the energy absorbed forever? Explain 
    your reasoning using physics concepts.
c. State and explain the scientific term used to describe a body that can 
     absorb or emit radiations that fall on them.
d. Basing on your ideas in question (c) above what could be the effect on 
     that body if:
    i) It maintains the energy for a long time
    ii) Reflects energy after a given time. 
   iii) Do you think that these reflected and absorbed radiations have effect 
        on the Climate? Why? Discuss your answers with your friends and even 
        present it to your Physics tutor
e. Some radiations may be prevented from leaving the atmosphere and 
     remain concentrated in the atmosphere. What do you think are effects of 
     these gases as they remain in the atmosphere?
f. In your own view what changes have been brought by this concentration 

     of radiations and how has man tried to control some of the changes.

     2.1 CLIMATE CHANGE

             Activity 2.1

The sun is the major source of energy (in form of radiation) on the earth. Some 
of these radiations are absorbed by different aerosols in the space and part of 
it reaches the earth. Our earth has special features that leads to absorption of 
these radiations and these processes are continuous.
a. What do you think are the effects of these radiations on the earth and its 
     atmosphere after absorption and reflection?
b. From your own understanding, what would happen if there is imbalance 
    between the absorbed and radiated energy in the earth’s atmosphere.
c. Can that incidence be controlled? How? 
d. With practical examples, discuss how these changes in climate have 
    been noticed in our country Rwanda 
e. In your own words, what are the scientific measures that can be done to 

    avoid that kind of situation?

2.1.1 Climate change and related facts

Climate is usually defined as the “average weather,” or more rigorously, as the 
statistical description in terms of the mean and variability of relevant 
quantities over a period of time ranging from months to thousands of years. The 
classical period is 3 decades, as defined by the World Meteorological Organization 
(WMO). These quantities are most often surface variables such as temperature, 
precipitation, and wind. Weather is measured in terms of the following parameters: 
wind, temperature, humidity, atmospheric pressure, cloudiness, and precipitation. 
In most places, weather can change from hour-to-hour, day-to-day, and season to-season. 
Climate can be described as the sum of weather. While the weather is 
quite variable, the trend over a longer period, the climate, is more stable.

However, climate change can be observed over a longer period of time. Climate 
change refers to any significant change in the climate parameters such as 
temperature, precipitation, or wind patterns, among others, that occur over several 
decades or longer Natural and human systems have adapted to the prevailing 
amount of sunshine, wind, and rain. While these systems can adapt to small 
changes in climate, adaptation is more difficult or even impossible if the change in 
climate is too rapid or too large. This is the driving concern over anthropogenic, or 
human induced, climate change. If climate changes are too rapid, then many natural 
systems will not be able to adapt and will be damaged and societies will need to 
incur the costs of adapting to a changed climate (REMA)

There has been variation in the atmospheric conditions in a given time. This has 
affected the seasons leading to a less output of our produce especially from 
agriculture, fishing and other activities.

These changes are sometimes for a short time but also may take a long time. Some of 
these changes result from our practices like farming, industrialization, urbanization, 
mining and other infrastructure developments. Care should be taken so as these 
changes in the atmospheric conditions can be avoided.

Some of important terms we need to know
    • Climate feedback: This refers to a process that acts to amplify or reduce 
       direct warming or cooling effects.
   • Climate lag: This is the delay that can occur in a change of some aspect 
     of climate due to the influence of a factor that is slow acting.
• Climate model: This is a quantitative way of representing the interactions 
    of the atmosphere, oceans, land surface, and ice. Models can range from 
    relatively simple to quite comprehensive

   This explains a delay that occurs in climate change as a result of some factors that 
   changes only very slowly. For example, the effects of releasing more carbon dioxide 
   into the atmosphere occur gradually over time because the ocean takes a long time 

    to warm up in response to these emissions.

      2.1.2 Causes of climate change.

Physics behind climate change and causes

The climate of the earth is controlled by its absorption and the subsequent emission 
of that energy.
The Earth’s surface temperature is determined by the balance between the 
absorption and emission of Sun’s radiation.
The major cause of climate change is the concentration of greenhouse gases, 
especially water vapor and carbon dioxide. These gases trap thermal radiation from 
the earth’s surface and this effect keeps the surface warmer than it would be.

a. Human causes
Human activities are major factors that lead to natural greenhouse effect. Most of 
activities done by human lead to high concentration of greenhouse gases. From 
research it has been found that the concentration of carbon dioxide has risen 
by about 30% in this period as compared to pre-industrial period. This gives a 
projection that the concentration of these greenhouse gases is still increasing day 
and night as people continue using fossil fuels.

Such activities include bush burning, burning of fossil fuels, deforestation and 
agriculture. All these activities have a strong impact on the climate of a given area 
as they may lead to either warming or cooling the land.

On another hand, industries have also led to the change in climatic conditions as 
they emit carbon gases into the atmosphere. From what is happening currently, 
the climatic conditions are worsening if the world becomes more industrialized. 
Peoples are trying to limit this by making machines that emit less carbon gases 

(REMA).

                     

 b. Natural causes

• Volcanicity: When volcanoes erupt, they throw out large volumes of 
Sulphur dioxide (SO2), water vapor, dust, and ash into the atmosphere. 
Although the volcanic activity may last only a few days, the large volumes 
of gases and ash can influence climatic patterns for years. Millions of 
tons of Sulphur dioxide gas can reach the upper levels of the atmosphere 
(called the stratosphere) from a major eruption.

• Ocean currents: Oceans plays a major role in the change of climate. 
Oceans cover about 71% of the Earth and absorb about twice as much of 
the sun’s radiation as the atmosphere or the land surface. Ocean currents 
move vast amounts of heat across the planet - roughly the same amount 
as the atmosphere does. But the oceans are surrounded by land masses, 

so heat transport through the water is through channels.

                Application activity 2.1 

1. Explain the meaning of the following terms.
a) Weather                                         d) Humidity
b) Climate                                           e) Temperature
c) Climatic change
2. What do you think are the factors that lead climatic change in your 
     area? Make a general conclusion using a case study of Rwanda.
3. Using Physics Concepts, discuss why different areas found in the 

     same region may have different climatic conditions.

      2.2 SOLAR AND BLACK BODY RADIATIONS.

              Activity 2.2

                         

The earth receives almost all its energy from the Sun’s radiation. The heat or 
energy from the sun prevents the earth from becoming cold and lifeless planet. 
Our earth is made in a way that it absorbs some of radiations from the sun and 
reflects some.
a. From your scientific understanding, what is the mode of transfer of energy 
from the sun to the earth?
b. Do you think all radiations that is emitted from the sun reaches the earth? 
Explain your reasoning.
c. Explain factors you think affect the intensity of radiations from the sun 
    received by the earth. 
d. From the introductory statement, it’s clear that the earth absorbs some 
    of the radiations from the sun. Discuss the factors you think makes the 
    earth absorb radiations.
e. From knowledge you acquired in unit 2 in year two, what is the scientific 
     name of the body that reflects absorbs radiations that falls on it. 

     2.2.1 Intensity of the sun’s radiation and albedo
Sun produces heat of very high intensity that is spread and then received by all 
surrounding objects. These objects include all the planets and other objects around 

it.

  

• The shape of the earth: The earth has a spherical shape and therefore the 
    sunlight is more spread out near the poles because it is hitting the earth at 
   an angle, as opposed to hitting the earth straight-on at the equator. There 
   are also fewer atmospheres at the equator, allowing more sunlight to reach 
   the earth. Therefore, the intensity varies depending on the geographical 
    latitude of the earth’s location.

• The earth’s rotation: all areas are not consistently exposed to sunlight. 
   Areas that are experiencing ‘night time’ are not receiving a lot of the sun’s 
   power; therefore, the time of the day or night will affect the solar constant.

• The angle of the surface to the horizontal at that particular location: When 
   the Sun is directly overhead, its rays strike Earth perpendicular to the 
   ground and so deliver the maximum amount of energy. When the Sun 
   is lower in the sky, a sunbeam strikes the ground at an angle and so its 

   energy is “spread out” over a larger area

The solar constant represents the mean amount of incoming solar electromagnetic 
radiation per unit area on the earth’s surface. This constant takes into account 
all types of solar radiation, including UV and infrared. The accuracy of the solar 
constant is questionable due to the following generalizations: This radiation is 
assumed to be incident on a plane perpendicular to the earth’s surface. It is 
assumed that the earth is at its mean distance from the sun. 

• Our seasons also determine how much Sun’s radiation strikes a square 
meter of ground in a given place on the planet’s surface at a given time of 
the year. The sun’s radiation is maximum in the summer and it is minimum 
in winter.

Scientists use a quantity called “albedo” to describe the degree to which a surface 
reflects light that strikes it. It can be calculated by the ratio of reflected radiation 

from the surface to the incident radiation upon it.

                       

The albedo has no units since it is a ratio of the similar quantities.

Being a dimensionless fraction, it can also be expressed as a percentage and is 
measured on a scale from 0 (0%) for no reflective power to 1 (100%) for perfect 
reflectors. The earth’s albedo is about 0.3, meaning, on average, 30% of the 
radiation incident on the earth is directly reflected or scattered back into space. An 
object that has no reflective power and completely absorbs radiation is also known 
as a black body

The table below gives you some values of estimated albedo for various surfaces 

expressed as percentages:

           
            

        2.2.2 Factors affecting earth’s albedo

Among other factors, the following are some of the factors that affect the albedo 
of the earth:
• Clouds. The atmosphere is usually covered with clouds that usually 
pass over the earth’s surface. This leads to reduction or increase in 
the temperature of the earth’s surface. This is because these clouds 
may absorb or reflects back sun’s light to the free space. However, this 
depends on the distance from which the clouds are from earth’s surface. 
When sun’s radiation is reflected, the earth’s surface is cooled and when 
it is absorbed the earth is warmed.

• Oceans While observing from the space, you will find out that water bodies 
appear differently from land surfaces. They appear darker and therefore 
absorb more sun’s radiations than land. However, some of the radiations 
heating the water surface (ocean) may be carried away by the currents 
while others may form water vapor. 

• Thick vegetation covers or forested areas. Places covered with vegetation 
absorb a lot of sun’s radiation. This is because the vegetation cover 
provides a dark surface which absorbs more radiations than the bare land. 

• Surface albedo. Different surfaces appear differently. Light coloured 
surfaces absorb different amounts of radiations than dark coloured 
surfaces. Snow covered areas are highly reflective. They thus absorb 
less amounts of energy (Sun’s radiation). The snow cover reduces the 
heating effect of the earth’s surface. However, if temperatures reduce, the 
snow cover reduces leading to the absorption of radiation by the exposed 

ground surface.

      2.2.3 Black body radiation

An object that absorbs all radiation falling on it and therefore emitting radiation in 
whole spectrum of wavelengths is called a blackbody. At equilibrium temperature, 
a blackbody has a characteristic frequency spectrum that depends only on its 

temperature. 

A perfect blackbody is one that absorbs all incoming light and does not reflect 
any. At room temperature, such object would appear to be perfectly black (hence 
the term blackbody). However, if heated to a high temperature, a blackbody will 
begin to glow with thermal radiation. 

Blackbody radiation is radiant energy emitted by an ideal black surface (blackbody) 
whose spectral power distribution is only governed by its own temperature. 
Blackbody radiation is radiant energy emitted by an ideal black surface (blackbody) 
whose spectral power distribution is only governed by its own temperature Black 
body radiation is the radiant energy emitted by a black body surface whose spectral 
power distribution is governed by its own temperature.

    LAWS OF BLACK BODY RADIATION

     a. Stefan-Boltzmann law

The law states that, “the power per unit area radiated by a surface of a black body 

is directly proportional to the forth power of its temperature”.

               

Using this formula, we can calculate the amount of power radiated by an object. A 
black body which emit in whole spectrum of wavelength would have an emissivity 

of 1.

Since the earth is not a perfect black body, it has a certain emissivity value.

                            
The emissivity is defined as the power radiated by a surface divided by the power 
radiated from a perfect black body of the same surface area and temperature.
 
In simpler terms, it is the relative ability of a surface to emit energy by radiation. A 
true blackbody would have an emissivity of 1 while highly polished silver could have 
an emissivity of around 0.02. The emissivity is a dimensionless quantity.

b. Wien’s displacement law 
It states that “the maximum wavelength of the emitted energy from a 
blackbody is inversely proportional to its absolute temperature”. 
This law was formulated by the German physicist Wilhelm Wien in 1893 who 
related the temperature of a black body and its wavelength of maximum emission 

following the equation.

        

Remember: It is not good to put on black clothes on a sunny day. This is because 
these dark clothes will absorb more radiations from the sun which may be harmful 

to our health.

      BLACK BODY RADIATION CURVES

               

This Fig.2.2 shows how the black body radiation curves change at various 
temperatures. The graph indicates that as the temperature increases, the peak 
wavelength emitted by the black body decreases. It therefore begins to move from 
the infra-red towards the visible part of the spectrum. Again, none of the graphs 
touch the x-axis so they emit at every wavelength. This means that some visible 
radiation is emitted even at these lower temperatures and at any temperature above 
absolute zero, a black body will emit some visible light. 

Features/Characteristics of the Graph 
• As temperature increases, the total energy emitted increases, because 
   the total area under the curve increases.
• It also shows that the relationship is not linear as the area does not increase 
  in even steps. The rate of increase of area and therefore energy increases 

  as temperature increases.

          Application activity 2.2

1. a. With clear explanations, explain the approximate spectral 
         composition of 
       the Sun’s radiation before it interacts with Earth’s atmosphere?
   b. Is the amount of solar energy that reaches the top of Earth’s 
       atmosphere constant? Explain giving valid examples and evidence.
   c. Are all wavelengths of Sun’s radiation transmitted equally through 
       Earth’s atmosphere? Explain your reasoning.
2. a. What effect does absorption have on the amount of solar radiation 
          that reaches Earth’s surface?
    b. List down other processes (besides absorption) that affect radiation 
         reaching the earth’s surface?
    c. What can be percentage of incoming solar radiation that is affected 
        by absorption and scattering (or reflection)?
3. a. Jane Says that clouds have a high albedo while Pierre says land 
        vegetation has a low albedo? Using Scientific explanations, discuss 
       what they base on to make their deductions.
   b. What do you think are major factors that influence the insolation at a 
       particular location on a particular day? How do they affect it?
    c. What latitudinal regions experience least variation in day-to-day solar 
       radiation? Which one experiences the greatest? Why?
4. a) Explain the meaning of a blackbody.

     b) Interpret Stefan-Boltzmann law and Wein’s displacement law.

     

            

         2.3 GREENHOUSE EFFECTS AND ITS IMPACT ON CLIMATE 

          CHANGE.

           Activity 2.3

               

a) What do you know about greenhouse?
b) Different activities like industrialization and others give out gases after 
     burning fossil fuels.
    i) What special name do you think is given to these gases?
    ii) If these gases accumulate in the atmosphere, what effect do they 
    have on to the temperature of the earth and its atmosphere?
c) Suggest measures that can be done to limit high accumulation of these 

      gases in the atmosphere.

Greenhouse effect is the process by which thermal radiation from the sun is 
prevented from leaving the atmosphere and then re-radiated in different directions.

The relationships between the atmospheric concentration of greenhouse gases 
and their radiative effects are well quantified. The greenhouse effect has the 
root from greenhouses that becomes warmer when heated by sun’s radiation. The 
mode of operation of a greenhouse is that a part of the sunlight radiations incident 
on the ground surface of the greenhouse are absorbed and warms the surface 
inside the greenhouse. Both the reflected radiations and the heat emitted by the 
ground surface in the greenhouse are trapped and re-absorbed inside the structure. 
Thus, the temperature rises inside the greenhouse compared to its surrounding 
environment.

Therefore, the greenhouse effect heats up the earth’s surface because the green 
gases that are in the atmosphere prevent radiations from leaving the atmosphere. 
The absorption of these radiations contributes to the increase of the atmosphere’s 
temperature.

A greenhouse is constructed by using any material that allows sunlight to pass 
through usually plastic or glass. This prevents reflected radiations from leaving 
the structure thereby leading to the increase in the temperature within. If a small 
puncture is made on to the greenhouse, the temperature within reduces. 

Since some of these re-radiated radiations come back to the earth’s surface, they 
lead to the increase in the temperature of the earth’s surface leading to global 

warming.

         

      2.3.1 Greenhouse gases

Some gases in the earth’s atmosphere act a bit like the glass in a greenhouse, 
trapping the sun’s heat and stopping it from leaking back into space.

Many of these gases occur naturally, but human activity is increasing the 

concentrations of some of them in the atmosphere, in particular:

      

2.3.2 Impact of greenhouse effect on climate change.

With the greenhouse effect, the earth is unable to emit the excess heat to space and 
this leads to increase in atmosphere’s temperature and global warming. Scientists 
have recorded about 0.75°C increase in the planet’s overall temperature during 
the course of the last 100 years. The increased greenhouse effect leads to other 
effects on our climate and has already caused: (REMA).
• Greater strength of extreme weather events like: heat waves, tropical 
   cyclones, floods, and other major storms.
• Increasing number and size of forest fires.
• Rising sea levels (predicted to be as high as about 5.8 cm at the end of 
   the next century).
• Melting of glaciers and polar ice.
• Increasing acidity in the ocean, resulting in bleaching of coral reefs and 
   damage to oceanic wildlife.

Solutions to reduce the impact of greenhouse gases
• High efficiency during power production
• Replacing coal and oil with natural gas
• Combined heating and power systems (CHP)
• Renewable energy sources and nuclear power
• Carbon dioxide capture and storage

• Use of hybrid vehicles.

2.3.3 Global warming

Global warming is the persistent increase in temperature of the earth’s surface 
(both land and water) as well as its atmosphere. Scientists have found out that the 
average temperature in the world has risen by about 0.750C in the last 100 years 
and about 75% of this rise is from 1975.

Previously the changes were due to natural factors but currently the changes are due 
to both natural and human activities. From research, Natural greenhouse maintains 
the temperature of the earth making it a better place for human kind and animal life. 
However ever since the evolution of industries, there has been significant change 
in the temperature. The causes are both natural and human activities and they are 
the ones that cause climate change.

Note: If these greenhouse gases were completely not there, the Earth would be 
too cold for humans, plants and other creatures to live.

Can you now see the importance of these greenhouse gases! Though they cause 
greenhouse effect, they are responsible for regulating the temperature of the earth.

Global warming is damaging the earth’s climate as well as the physical environment. 
One of the most visible effects of global warming can be seen in the Arctic region 
where glaciers, permafrost and sea ice are melting rapidly. Global warming is 
harming the environment in several ways. Global warming has led to: Desertification, 

Increased melting of snow and ice, Sea level rise, stronger hurricanes and cyclones.

         Application activity 2.3

1. Differentiate the term “greenhouse effect from global warming.
2. With clear explanations, explain why it is called the “greenhouse” 
    effect?
3. From your own reasoning and understanding, why do you think 
    Environmental experts have become worried about the greenhouse 
     effect?
4. Below is a bar graph showing emitted Greenhouse gases worldwide 

     from 1990 to 2005. Use it to answer the questions that follow

                     

a) From your analysis (using the graph) which kind of gas was emitted in 
     excess for the specified period?
b) What could be the factors that led that gas to be emitted in large 
    quantities?
c) What do you think one can do to limit such emissions?
d) From your own point of view, do you think it’s a good idea to stop 
     completely emission of these gases? Explain your reasoning by giving 

      valid examples

      2.4 CLIMATE CHANGE MITIGATION

             Activity 2.4

Read the text below and answer the questions that follow.
The government of Rwanda is trying to sensitize people not to cut down trees 
for charcoal, drying wetlands for farming activities and regulating people from 
approaching wetlands, forests (Both Natural and artificial) and Fighting all 
activities that may lead to climate change.
       a. As a good citizen of Rwanda, do you support these plans of the 
           government? Support your stand with clear justifications
      b. If yes what have you done to implement some of these policies?
      c. What are some of the New Technologies that the government is 

          advocating for to stop these negative climate changes?

2.4.1 Climate change mitigation

Climate change mitigation refers to efforts to reduce or prevent emission of 
greenhouse gases. Mitigation can mean using new technologies and renewable 
energies, making older equipment more energy efficient, or changing management 
practices or consumer behavior. (IPCC, 1996)

Climate change is one of the most complex issues we are facing today. It involves 
many dimensions science, economics, society, and moral and ethical questions 
and is a global problem, felt on local scales that will be around for decades and 
centuries to come. Carbon dioxide, the heat-trapping greenhouse gas that has 
driven recent global warming, lingers in the atmosphere for centuries, and the earth 
(especially the oceans) takes a while to respond to warming.

So even if we stopped emitting all greenhouse gases today, global warming and 
climate change will continue to affect future generations. In this way, humanity is 
“committed” to some level of climate change.

Because we are already committed to some level of climate change, responding to 
climate change involves a two-pronged approach:
1. Reducing emissions and stabilizing the levels of heat-trapping greenhouse 
    gases in the atmosphere (“mitigation”);

2. Adapting to the climate change already in the pipeline (“adaptation”).

2.4.2 Mitigation and adaptation

Because of these changes in climatic conditions, man has devised all possible 
measures to see how he can live in harmony on this planet. This has made man to 
think harder so that these greenhouse gases can be minimized.

The process of preventing all these greenhouse gases is what is known as 
mitigation. This is very important as it is aimed at controlling the rise in temperatures 
of the earth while regulating earth’s temperature.

The main goal of mitigation is to reduce human interference to nature thereby 
stabilizing the greenhouse gas levels in a given time to allow ecosystem to adapt 
naturally to the climate changes. Care should be taken while these adjustments are 
made not to affect food production and other economic developments.

Among other strategies, mitigation strategies include: 
a) Retrofitting buildings: Retrofitting is the process of modifying something 
after it has been manufactured.

Retrofitting a building involves changing its systems or structure after its initial 
construction and occupation. This work can improve amenities for the building’s 
occupants and improve the performance of the building. As technology develops, 
building retrofits can significantly reduce energy and water usage hence conserving 
energy sources.

Retrofitting has come to prominence in recent years as part of the drive to 
make buildings more thermal efficient and sustainable. This can help cut carbon 
emissions, make it cheaper and easier to run buildings, and can contribute to 
overcoming poor ventilation and damp problems.

b) Adopting renewable energy sources like solar, wind and small hydroelectric plants:
Human activities are overloading our atmosphere with carbon dioxide and 
other global warming emissions. These gases act like a blanket, trapping heat. The 
result is a web of significant and harmful impacts, from stronger, more frequent 
storms, to drought, sea level rise, and extinction.

In contrast, most renewable energy sources produce little to no global warming 
emissions. Even when including “life cycle” emissions of clean energy (ie, the 
emissions from each stage of a technology’s lifemanufacturing, installation, 
operation, decommissioning), the global warming emissions associated with 
renewable energy are minimal.

c) Helping cities develop more sustainable transport such as bus rapid 
     transit, electric vehicles. This helps in reducing carbon emissions.
d) Promoting more sustainable uses of land and forests and making people 
     aware of the impacts of mis-using these natural gifts.

e) Creating carbon sinks like in big oceans in case there are no alternatives.

        

            Application activity 2.4

1. Plan and write an essay about climatic change mitigation in Rwanda. 
2. Make a research about climate change mitigation in your 
       neighborhood (either for the school or for your home) and answer 
       the following questions.
a) What are some of the conditions you have experienced that used in 
      order to prevent the greenhouse gases?
b) How have you adapted to the changes in conditions you have 
     mentioned in a) above.

c) What are you doing to stop these climatic changes?

                                           Skills Lab 2

Aim: Constructing a greenhouse. (Can be done over a long period 
of time)
In this activity you may need
• Polyethene paper (should be relatively white in color)
• Wood
• Nails
• Any fiber that can be used while tying 
• Laboratory thermometer.

• Bean seeds

Procedures 

a) Collect materials listed above.
b) Chose a place where to construct the greenhouse. It may either be near 
     your school or near your home.
c) Fix and connect the materials together until you make a structure similar 

      to the one indicated in the figure below.

                             

d) Each day measure temperatures and keep noting down records.
e) What do you think are the causes of temperature variations in your 
    records?
f) Sow seeds of beans in your greenhouse.
g) After seeds have germinated, keep observing changes in the development 
    of the bean plant.
h) Make a comprehensive report about your Greenhouse. (Include 
     temperature and vapor changes within the greenhouse).

i) Share it with your friends or your physics tutor.

                      End of unit 2 assessment

Re-write the questions (1) to (8) below in your notebook and circle the best 
alternative 
1. The emissivity (ε) can be defined as the ratio of
       A. emissive power of real body to the emissive power of black body
       B. emissive power of black body to the emissive power of real body
      C. reflectivity of real body to emissive power of black body
      D. Reflectivity of black body to emissive power of real body.
2. Imagine two planets. Planet A is completely covered by an ocean 
    and has and overall average albedo of 20%. Planet B is blanketed 
    by clouds and has an overall average albedo of 70%. Which planet 
     reflects more sunlight back into space? 
    A. Planet A
    B. Planet B 
    C. the two planets reflect the same amount of light
    D. more information is needed to answer this question 
3. _______________ is a term used to a process that acts to amplify or 
           reduce direct warming or cooling effects
      A. Climate change                           C. Climate feedback
      B. Weather                                          D. Climate model
4. The filament of an electric bulb has length of 0.5 m and a diameter 
     of 6x10-5 m. The power rating of the lamp is 60 W Assuming the 
     radiation from the filament is equivalent to 80% that of a perfect 
    black body radiator at the same temperature. The temperature of the 
     filament is (Stefan Constant is 5.7x10-8 Wm-2K-4):
     A. 1933 K                                          C. 64433333.3 K
    B. 796178.3 K                                  D. 60 K
5. The long-term storage of carbon dioxide at the surface of the earth 
     is termed as
    A. Black body radiation              C. Solar radiation management
    B. Thermal expansion                 D. Sequestration
6. The balance between the amount of energy entering and exiting the 
     Earth system is known as
        A. Radiative balance C. Paleoclimatology
       B. Black body Radiation D. Solar radiation
7. The following are examples of greenhouse gases except 
      A. Carbon dioxide C. Methane 
      B. Nitrous oxide D. Oxygen
8. The government of Rwanda is advising the people to conserve the 
     nature. This is intended to limit the incidence of rise in the temperature. 
    This conservation of nature
   A. Reduces the amount of water vapor that leads to increase in 
       temperature
  B. Reduces the amount of Carbon dioxide in the space
  C. Increases the amount of plant species that is required to boost our 
       tourism industry
  D. Provides a green environment for human settlement
9. a) State Wien’s displacement law and its practical implications

     b) Use the graph indicated below to answer the questions that follow

                        

     i) What does the graph explain? 
    ii) Explain the spectrum that is found between temperatures of 4000 
         and 7000 K
   iii) Why do you think the three curves have different shapes 
10. Discuss any 4 main reasons that brings about variation of sun’s Intensity
11. a) Calculate the albedo of a surface that receives 15000 Wm-2 and 
            reflects 15 KW.m-2.Comment on the surface of that body.
       b) Discuss some of the scientific factors that affect planets Albedo
12. a) What do you understand by the following terms?
              i) Climate change as applied in physics 
             ii) Greenhouse Effect
      b) With Clear explanations, discuss how Greenhouse effect can be 
avoided
13. Mutesi a year 3 student in the faculty of engineering in University of 
      Rwanda, found out in her research that a strong metal at 1000K is 
    red hot while at 2000K its white hot. Using the idea of black body, 
     explain this observation.
14. Kamari defined black body as anybody that is black. Do you agree 
      with his definition? If YES why? and if NOT why not? Also sketch 
      curves to show the distribution of energy with wavelength in the 
      radiation from a black body varies with temperature.
15. An electric bulb of length 0.6 m and diameter 5 x 10-5m is connected 
      to a power source of 50 W. Assuming that the radiation from the 
      bulb is 70% that of a perfect black body radiator at the same 
      temperature, Estimate the steady temperature of the bulb. (Stefan’s 
       constant = 5.7 x 10 - 8 W m 2 K-4.) 
16. Write short notes about greenhouse effect and explain all its effects.
17. What do you understand by the term greenhouse gases? How do 
       these gases contribute to the global warming?
18. REMA is always advising people to plant more trees and stop 
      cutting the existing ones. Using scientific examples, explain how this 
       is aimed at controlling global warming
19. Explain climate change mitigation and explain why it’s important.
20. Explain what happens to most radiation that is absorbed by the 
       surface of earth?
21. Is there a difference between sensible and latent heat?
22. Write short notes on the following terms as applied in climate change
        i) Climate feedback
       ii) Climate lag
      iii) Climate model
23. Plan and write a good composition about causes of climate change 
       and how it can be controlled. (Your essay should bear introduction, 

        body and conclusion)