Lecture 3: Energy Basics and Uses

Question 1

First Law of Thermodynamics

Answer 1

Energy is Conserved
Energy can be neither created nor destroyed
- The flow of heat is a form of energy transfer
- performing work is a form of energy transfer

Question 2

Forms of Energy

Answer 2

MECHANICAL (m)
- Kinetic
- Gravitational Potential
- Elastic Potential
THERMAL (t)
ELECTRICAL (e)
RADIANT (r)
CHEMICAL (c)
ATOMIC (a)

Question 3

Mechanical Energy (m)

Answer 3

- Force: mass and acceleration F = ma
Units for force - Newton (N), Pounds (lb)
- Work: force over a distance W = fd
- Potential Energy: mass, height, gravity
Epot = mgh
- Kinetic Energy: mass and velocity 
Ekin = 1/2 mv2
Wind Power: density, area, velocity 
Pwind = 1/2pAv3
Units energy per second (W, hp)

Question 4

Thermal Energy (t)

Answer 4

Heat is kinetic energy at the molecular level

Heat capacity is the ability for materials to store energy

Question 5

Electrical Energy (e)

Answer 5

• I = current (amps)
• R = resistance (ohms)
• V = voltage
• Electrical Power (Watts, VA)

Question 6

Radiant Energy (r)

Answer 6

• Travels by waves
• Electromagnetic radiation
• Acoustic waves

Question 7

Chemical Energy (c)

Answer 7

• Energy is stored in chemical bonds of molecules
• Fuel molecules release that chemical energy during combustion
• Responsible for > 80& energy in the world

Question 8

Atomic Energy (a)

Answer 8

Energy is stored in the nucleus of atoms
20,000 times more energy density than coal
6.6 g dissappear

Question 9

Different types of conversions

Answer 9

Thermomechanical: Heat to motion t->m
Thermochemical: Chemical energy to heat
c->t
Thermonuclear: heat from nuclear a->t
Electrochemical: chemical reactions to electricity e->c
Electromechanical: generators, electric motors
e->m
Photoelectric/photovoltIaic: light to electricity
e->r
Photochemical: Phothosythesis
c->r

Question 10

Second Law of Thermodynamics

Answer 10

• Entropy increases
• inefficiencies
• Losses always occur
• systems move from low entropy to high entropy

Question 11

Overall Efficiency from chemical to light energy

Answer 11

1.6%

Question 12

Wasteful Electricity System

Answer 12

40 quads of fuels to get 13 Quads of electricity