Day 1
Hour 1
Read "The iPhone's Biggest Flaw" (a Word or PDF version)
In your group, discuss the following questions:
Group Worksheet
Hour 2
Redox Review
We've been studying how wind or mechanical energy can be converted into electrical energy. Electrical energy is electrons moving through wires. But where do these electrons come from? Can this electrical energy be stored? How do you catch a moving electron and release it when and where you want it? To answer this, you need to review some chemistry.
Electrons swirl around all atoms. When they are shared between atoms they form bonds that keep the sharing atoms tightly together in molecules. However, electrons are not permanently attached to any particular atom or molecule. And when they decide to jump to a different location, energy is always involved. If the electrons' new home is lower in energy (more stable), energy is released into the environment, usually as heat (exothermic). If the new home is higher in energy, the extra energy came from the surroundings (endothermic). Which happens depends on the details of what atoms and molecules are involved. In exothermic cases when the electrons jump directly from one atom to another, the energy can be released quickly and powerful explosions can result. Combustion in your car's engine is an example.
Reactions that transfer electrons between atoms are called oxidation/reduction reactions, or redox for short. From an energy point of view, redox reactions are the most useful chemical reactions around. That's because they involve valence electrons (usually in chemical bonds) which can be easily accessed (unlike the core electrons or nuclear binding forces which are much harder to get at). As bonds are broken and formed, electrons move from one element to another, often releasing large amounts of energy. Watch the Mythbuster guys use a powerful redox reaction to melt a car.
Here's the thermite reaction used in the Mythbuster video:
Fe2O3 + Al → Fe + Al2O3
So what is being oxidized? What's reduced? Can you balance it?
Sometimes we don't want all the energy for a given redox reaction to be released all at once. It would be hard to use the thermite reaction to power your cell phone. To capture the energy from a redox reaction gradually, on demand, we convert it into electricity. In this trick, we force the electrons that leave the oxidized atom to pass through a wire to get to the atom being reduced. We call a redox reaction constrained in this way a battery. In every battery, a redox reaction is being tapped to transfer electrons from one atom or compound to another. By tricking the electrons to pass through a wire as they are transferred, the electrons can do electrical work along the way.
We will see first hand how batteries do this magical feat when we build a battery later this week, but let's first review some chemistry to learn what oxidation and reduction is. Watch the Khan Academy Videos on Oxidation/Reduction (REDOX). Then complete the worksheet on oxidation numbers.
Hour 1
Read "The iPhone's Biggest Flaw" (a Word or PDF version)
In your group, discuss the following questions:
- What are ways you consciously or unconsciously conserve your phone battery?
- How would you use your phone differently if you weren't afraid of running out of juice?
- What would you be willing to pay for a battery that lasted all day with maximum usage?
- How much more capacity do you think a phone battery needs?
- Do you agree that battery energy capacity is the biggest flaw in smart phones?
- What other flaws would you like "fixed"?
- Is the author picking on iPhones unfairly? Why or why not?
- The author mentions that a significant improvement was achieved by increasing the voltage of the battery by just 0.1 V. How do you think this was achieved?
- How are app developers affected by inadequate batteries?
- Do you think it will ever be possible to create a phone battery that is "big enough"? Why or why not?
- Size or capacity? Which is more important? Why?
Group Worksheet
Hour 2
Redox Review
We've been studying how wind or mechanical energy can be converted into electrical energy. Electrical energy is electrons moving through wires. But where do these electrons come from? Can this electrical energy be stored? How do you catch a moving electron and release it when and where you want it? To answer this, you need to review some chemistry.
Electrons swirl around all atoms. When they are shared between atoms they form bonds that keep the sharing atoms tightly together in molecules. However, electrons are not permanently attached to any particular atom or molecule. And when they decide to jump to a different location, energy is always involved. If the electrons' new home is lower in energy (more stable), energy is released into the environment, usually as heat (exothermic). If the new home is higher in energy, the extra energy came from the surroundings (endothermic). Which happens depends on the details of what atoms and molecules are involved. In exothermic cases when the electrons jump directly from one atom to another, the energy can be released quickly and powerful explosions can result. Combustion in your car's engine is an example.
Reactions that transfer electrons between atoms are called oxidation/reduction reactions, or redox for short. From an energy point of view, redox reactions are the most useful chemical reactions around. That's because they involve valence electrons (usually in chemical bonds) which can be easily accessed (unlike the core electrons or nuclear binding forces which are much harder to get at). As bonds are broken and formed, electrons move from one element to another, often releasing large amounts of energy. Watch the Mythbuster guys use a powerful redox reaction to melt a car.
Here's the thermite reaction used in the Mythbuster video:
Fe2O3 + Al → Fe + Al2O3
So what is being oxidized? What's reduced? Can you balance it?
Sometimes we don't want all the energy for a given redox reaction to be released all at once. It would be hard to use the thermite reaction to power your cell phone. To capture the energy from a redox reaction gradually, on demand, we convert it into electricity. In this trick, we force the electrons that leave the oxidized atom to pass through a wire to get to the atom being reduced. We call a redox reaction constrained in this way a battery. In every battery, a redox reaction is being tapped to transfer electrons from one atom or compound to another. By tricking the electrons to pass through a wire as they are transferred, the electrons can do electrical work along the way.
We will see first hand how batteries do this magical feat when we build a battery later this week, but let's first review some chemistry to learn what oxidation and reduction is. Watch the Khan Academy Videos on Oxidation/Reduction (REDOX). Then complete the worksheet on oxidation numbers.