Basic Concepts

1. Describe the nature of the following terms:

2. Describe a circuit. It is a conductive loop that allows a current or flow of charge to circulate. Resistance in a circuit tends to convert the electrical energy that keeps the current flowing into heat. Hence, energy has to be continuously added to the circuit to keep the current flowing. This can be done with a device such as a battery, fuel cell, solar cell, or generator.

3. Describe the two key elements of conventional current.

   flows from high voltage to low voltage

   flows from the positive side of a battery to the negative side

   considered to be positive charges.

4. Name the direction, the type of charge and its associated particle that really flows in most circuits. Most circuits means one in which the pathways between elements (such as batteries, motors, light bulbs, etc.) are made of a metal.

   the opposite direction of the current, from low to high voltage

   negative charges

   electrons

5. State the difference between the term voltage and voltage difference.

   voltage refers to the level of electrical potential energy at a specific location.

   voltage difference refers to the change in electrical potential energy from one point in a circuit to another.

6. State why a bird can land on a high voltage transmission with without being electrocuted. While some charge does initially flow into the bird, afterwards, there is not voltage difference across the bird. In other words, the bird does not become part of an electrical circuit.

Homefun (formative/summative assessment): Read sections

Formative Assessment: Physics Investigation

Follow up Questions

How is Voltage Measured?

7. Evaluate the saying, "it's not the voltage that kills, it's the current."

   a person can be subjected to high voltage without serious injury if they are not part of a circuit that allows a significant current to flow through them.

   A person will be suffer injury or death if a significant current flows through them.

   On the other hand, voltage and current are related. A voltage difference across a person of as little as 30 volts can cause injury or death.

8. Explain the difference between AC and DC electrical power and why is this important to know when measuring voltage.

   AC -- alternating current flows back and forth. To do this voltage flip flops between positive and negative values.

   DC -- direct current flows in one direction. The sign on voltage remains constant.

9. Describe how a battery or other source of electrical power analogous to a pump. A pump sending water to a water tower is increasing the water's gravitational potential energy. A battery sending current around a circuit is increasing the electrical potential energy of the charge flowing through it.

10. Sketch batteries in parallel and in series. State reasons for each type of battery configuration.

    Parallel -- voltage is the same but battery life is longer

    Series -- voltage is higher

11. What does resistance in a circuit or electrical component do? It turns electrical energy into heat.

12. State the internal resistance of an ideal voltmeter and explain why this level of resistance is required.

    Infinite resistance. Note that real voltmeters have very high but not infinite resistances.

    Less resistance alters the voltage being measured. Real voltmeters do slightly alter the measured voltage.

13. Sketch how a voltmeter (voltage measuring device) should be connected to an element of a circuit in order to measure voltage. in parallel

14. Measure voltages using a voltmeter.

Relevance: Voltage measurements are a basic tool for troubleshooting any type of electrical equipment including batteries, stereo equipment, automobile engines, etc..

Homefun (formative/summative assessment) . read 22.1

Ohm's Law

16. Recognize when the items in a circuit are in connected in series or in parallel.

    parallel -- the items are connected to parallel wires. Items in parallel always have the same voltage drop across them.

    series -- the items are connected end to end (sometimes with wire in between them) so that the current passing through them is always the same.

17. State the internal resistance of an ideal ammeter (current measuring device) and explain why this level of resistance is required.

    Zero resistance. Note that real ammeters have very low but not zero resistances.

    Resistance in an ammeter will reduce the current being measured. Real ammeters do slightly alter the measured current.

18. Sketch how an ammeter should be connected in a circuit in order to measure voltage. in series

19. Measure currents using an ammeter.

20. State and explain Ohm's Law.

I = V / R

where:

I = current

V = voltage difference across the resistance

R = resistance

21. Solve problems with Ohm's Law.

22. Combine resisters in series and resisters in parallel.

    Series: (total resistance) = R1 + R2 + ... + Rn

    Parallel: 1 / (total resistance) = 1/R1 + 1/R2 + ... + 1/Rn

Relevance: Ohm's Law is the most basic equation in electricity and the multimeter the most basic tool. They are used, not just by scientists and engineers but also by electricians, linemen (people who work on power lines), auto mechanics, and hobbyists.

Homefun (formative/summative assessment): problems 6, 7, 8, page 598

Power

24. Give a general definition of power. (work done or energy used) / (time interval)

    for electrical circuits: power = V(I)

25. State the unit for power. Watt = joule / sec
26. Derive two additional equations for electrical power by combining Ohm's Law with the basic electrical power equation.

    power = (V^2) / R

    power = (I^2) R

27. Solve electrical power problems given the 3 possible equations.

28. Explain why the devices using electrical power are all connected in parallel rather than series.

    electric utilities provide constant voltage

    in parallel the power consumption of devices are independent, a necessity for proper operation.

29. Calculate the total power load on a parallel circuit by adding the individual power consumptions of the devices attached to it.

30. Work circuit breaker problems.

31. Given power, time, and cost per unit of energy calculate energy consumption and cost.

Relevance: A basic understanding of power consumption and circuit breakers is can prevent both fires and the loss of electrical power.

Homefun (formative/summative assessment): section review 28 and 29 page 605.

Review

Formative Assessments:

1. Work review problems at the board

2. Work practice problems.

Metacognition Problem Solving Question: Can I still work the problems done in class, several hours or days later? Some amount of repetition on the exact same problems is necessary to lock in learning. It is often better to thoroughly understand a single example of a problem type than to work example after example understanding none of them completely.

Relevance: Good test preparation is essential to performance in physics class.

Homefun (formative/summative assessment): turn in on the day stapled to the back of the test.

Summative Assessment: Unit exam objectives 1-23