Examples In a certain room in your house, you use a 100 W light bulb. This light is on for 5 hours every day. How much energy does it use? 1 W = 1 J/s and there are 5h x 60min/hour x 60 sec/min = 18,000s in 5 hours so the total energy used is 100 j/s *18000s = 1.8 x 10 6 J. Lets assume the same lighting level can be achieved using a 30 W compact florescent bulb. How much energy is used by the compact florescent bulb?

Examples Total energy = 30 j/s x s = 5.4 x 10 5 j. So how much energy is saved every day using the compact florescent bulb? Take the difference between the energy used by the two different light bulbs: 1.8 x 10 6 j x 10 5 j = 1.3 x10 6 j. Lets look at this in something you might be able to relate to better than joules---dollars!

Example continued After 5 hours, our 100 W light bulb uses 500 Watt-hours, or 0.5 Kwh. The 30 W bulb will use 150 Watt hours or 0.15 Kwh. Assume electricity costs 11 cents/Kwh (average cost in the US in April 2008). So it costs.5 KwH x 11 cents/Kwh = 5.5 cents every day to run the 100 W light bulb and 0.15Kwh x 11 cents = 1.65 cents every day to run the compact florescent.

Example continued So in a year, the 100 W light bulb costs you 5.5 cents/day X 365 days/year = $20.00 and the 30 W bulb costs costs you 1.65 cents/day x 365 days/year = $5.50.

Types of Energy: kinetic and potential Energy Kinetic energy - energy of a moving object KE=1/2mv 2 Potential Energy – Energy stored in a system, for example an object of mass m, a distance h above the surface of the earth has a potential energy given by mgh. g is the acceleration due to gravity = 9.8 m/s2

More examples of potential energy Another example is a spring, compressed a distance x from its equilibrium point has a potential energy 1/2kx 2, where k is the spring constant, a property of the spring.

Chemical Energy Energy that is released via chemical reactions. Often times release is through combustion such as energy generation via coal Another example is a battery

Heat Energy Temperature Scales: Fahrenheit – based on the height of liquid (often mercury or alcohol) in a glass tube. Celsius – another scale using height of liquid in a tube Kelvin-absolute scale – True measure of energy Energy associated with the random motions of the molecules in a medium. Measured by temperature

Fahrenheit temperature scale Freezing point of water set at 32 and boiling point set at 212, so there is 180 degrees between them and each degree is 1/180 of the difference between these two points.

Celsius temperature scale Freezing point of water set at 0 and boiling point set at 100, so there is 100 degrees between them and each degree is 1/100 of the difference between these two points.

Kelvin temperature scale O k is absolute zero. All molecular motion stops. Interval set so that 1 k = 1 c So to convert from c to k k=c+273

Mass Energy E = mc 2 Energy and mass are equivalent C = 3 x 10 8 m/s. A big number and its squared! So even if m is small, E is big. A small mass, converted to energy, gives a lot of energy!

Example

Electromagnetic energy Light displays properties of both waves and particles. Light is an electromagnetic wave-a wave created by alternating electric and magnetic fields. “Light” is more than just visible light, it covers wavelengths from radio thru Gamma rays Light is also a “particle” called a photon. Photons have energy given by E=hν or E=hc/λ. H is constant, c is the speed of light, ν is the frequency of light and λ is the wavelength of the light.

Conservation of Energy The principle of conservation of energy states that energy cannot be created or destroyed. But it can be converted form one form to another This idea of energy transformation is at the heart of energy generation.

Energy Sources renewable vs non- renewable Renewable – can’t be exhausted Solar Geo-thermal Tidal Wind Hydro Non-renewable-can be exhausted Fossil fuels (oil, coal etc) uranium

How much do we use? World energy consumption US energy consumption

How much do we use?

Almost 95% of the energy we use comes from non-renewable energy sources! One of these days we will run out, and then what? What are some short and long term answers to this question?