1.1 Hewitt Chapter 22 Electrostatics

Please read Hewitt Electrostatics Chapter 22 and answer the following questions in complete sentences.

Can you create or destroy charge? Why or why not?
Why is charge usually transferred by electrons instead of protons?
For the same object, which is more massive, a negatively or positively charged object? Explain why and how big a difference in mass you’d see.

1.2 Energy and Power Conceptual

You have a device running at constant power P that consumes E units of energy in a time t. If I double the power and leave everything else the same, what happens to the energy used?

You have a device running at constant power P that consumes E units of energy in a time t. How much energy is consumed if I double the time that the device runs?

1.3 Battery Charger Power

You have a battery charger that uses 2 amps when charging from a 120V wall source.

How much power does the charger draw from the wall in watts?
How much energy is used if the charger runs for 6 hours in kilowatt-hours?
What is the energy above in Joules?

1.4 Hewitt Chapter 23 Electric Current

Please read Hewitt Electrostatics Chapter 23 and answer the following questions in complete sentences. Note Chapter 23 is in the second half of this PDF file.

What two things need to be present for an electric current to form?
Will current flow more easily through a thick wire or a thin wire?
Why do wires carrying large currents become hot?

1.5 Electrify Everything

Please read the linked article and answer the following questions.

In your own words, what are the three main reasons for electrification from a climate perspective according to the article?
Describe the problem of the “duck curve” in your own words.

2.1 Pencil Lead Resistivity

When I place 1V across a piece of 0.9 mm diameter, 60mm long pencil lead, 1 amp of current flows.

What is the resistance of this pencil lead in ohms?
What is the resistivity of the pencil lead material in ohm-meters?
Draw an IV curve for this item and clearly label the slope and axes.

2.2 REEPS Chapter 2 Circuits

Chapter 2 has a more in-depth treatment of our concepts. Review the chapter and answer the following question.

Which part of the chapter is clearest and why?

If the library link above isn’t working here is an alternate.

2.3 Pencil Lead Resistance

A graphite pencil lead behaves like a resistor. Assume the pencil graphite has a resistivity of 4 \cdot 10^{-5} ohm-m. A mechanical pencil lead is 0.9mm in diameter and 60 mm long.

What resistance do you calculate for this? (should be about 4 ohm)

2.4 EV Charger Cable

You are designing a very fast electric vehicle charger that supplies 300 amps of current at 400 volts. You have to limit the resistance in the charging cable to very low values to prevent dangerous heat buildup.

What does the total resistance of your cable need to be in milliohms to limit the dissipated heat to 100W?

3 Toaster Oven

A toaster oven has a resistance of 24 \Omega. At a voltage of 120V

Draw a circuit diagram with the voltage source and the toaster as a resistance.
What is the current through the toaster?
How many watts of power does the toaster draw?

4 Resistor IV Curve Intersection

Imagine you have a 4 ohm resistor connected to a 12 volt ideal power supply.

Draw and label the IV curve for the resistor and the supply
Show how the IV curves relate to what Ohm’s law predicts for the current
Shade the area that shows the power dissipation in the resistor.
Draw the curve for a 2 ohm resistor (keeping the power supply the same) and comment on what changes.

5 Series Resistors Reasoning

I have a voltage source connected to a resistor. If I add a second resistor in series with the first,

Will the current go up or down?
Will the power delivered go up or down?

Provide reasons for your answers.

6 Parallel Resistors Reasoning

I have a voltage source connected to a resistor. If I add a second resistor in parallel with the first,

Will the current go up or down?
Will the power delivered go up or down?

Provide reasons for your answers.

7 Find Equivalent Resistance Parallel

You have two resistors in parallel with values of 10 ohms and 20 ohms. What is the value of a resistor that would have the same IV curve as these together?

8 Find Equivalent Resistance Series

You have two resistors in series with values of 10 ohms and 20 ohms. What is the value of a resistor that would have the same IV curve as these together?

9 Parallel Currents and Voltages

You have two resistors in parallel with values of 10 ohms and 20 ohms. These resistors are connected to a 10 volt supply.

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what is the current through each resistor?
what is the voltage across each resistor?
what is the power dissipated in each resistor?
what is the power delivered by the supply?

10 Series Currents and Voltages

You have two resistors in series with values of 10 ohms and 20 ohms. These resistors are connected to a 10 volt supply.

what is the current through each resistor?
what is the voltage across each resistor?
what is the power dissipated in each resistor?
what is the power delivered by the supply?

11 Circuit Breaker

You have a 15 amps circuit breaker for a 120V line. How many 20 ohm loads can you put in parallel on this circuit before you exceed the circuit breaker trigger?

12 Predict-Observe Series

You have two bulbs in series with a voltage source. If I unplug R1 what happens to the brightness of bulb R2?

increase, stays same, decrease, turn off?

13 Predict-Observe Parallel

You have two bulbs in parallel with a voltage source. If I unplug R1 what happens to the brightness of bulb R2?

increase, stays same, decrease, turn off?

14 Predict-Observe Parallel Distribution

You have two bulbs in parallel with a voltage source. If I unplug R1 what happens to the brightness of bulb R2 and R3?

R3 increase, stays same, decrease, turn off?
R1 increase, stays same, decrease, turn off?

15 Power Shutoff and Wildfire Risk

Please read the linked article on California Public Safety Power Shutoffs (PSPS) and answer the following questions.

How have you been affected by PSPS events?
What do you think California and PG&E should do differently?
Where do you think revenue for these changes would come from?

16 Duck Curve Reading

Please read this Vox article and interview on the utility duck curve and answer the following questions.

Name any acronyms or concepts you haven’t seen before
Which grid participants consider the duck curve a problem and why?
What ways are folks addressing the duck curve?