Mr. Rogers' Honors Physics Syllabus 1st Quarter 2nd Quarter 3rd Quarter 4th Quarter Waves (14) Sound (15) E-Fields (21) Electricity (22) & Circuits (23) Magnetics (24) & (25)

Electricity-- Chapter 22

Relevance: Electrical equipment is ubiquitous. Some knowledge of it is very helpful for troubleshooting equipment both as an employee, hobbyist or do-it-yourselfer.

 SC Standards : Indicators P-4.3 Summarize current, potential difference, and resistance in terms of electrons. P-4.4 Compare how current, voltage, and resistance are measured in a series and in a parallel electric circuit and identify the appropriate units of measurement. P-4.5 Analyze the relationships among voltage, resistance, and current in a complex circuit by using Ohm's law to calculate voltage, resistance, and current at each resistor, any branch, and the overall circuit. P-4.6 Differentiate between alternating current (AC) and direct current (DC) in electrical circuits. P-4.7 Carry out calculations for electric power and electric energy for circuits. P-4.8 Summarize the function of electrical safety components (including fuses, surge protectors, and breakers). P-4.11 Predict the cost of operating an electrical device by determining the amount of electrical power and electrical energy in the circuit.

 Practice Test Study Guide
 Objectives
 Essential Question: What does voltage do?

Basic Concepts

1. Describe the nature of the following terms:
term description unit basic units analogous to:

voltage

other terms: potential, potential difference, EMF (electromotive force)

electrical potential energy per unit of charge. Note: voltage is not a force or a pressure! volt
 Joule Coulomb

the height of a water tower. The higher the water tower, the greater the gravitational potential energy per unit of mass.

current flow of charge ampere
 Coulomb sec.
a flow of water in a pipe
resistance tendency to restrict the flow of charge ohm
 J ∙s C2
a valve or the internal friction inside a pipe that restricts the flow of water
1. 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.

2. 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.

3. 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

4. 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.

5. 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.

 Formative Assessment: Physics Investigation Title Twiddler's Delight (TD) Investigation Research Question What causes the opposite shaft of the TD to rotate when the shaft on the other end is manually spun? Background The scientific method has 4 steps, 1) formulate a research question, 2) hypothesize how the research question can be answered, 3) design an experiment to test the hypothesis, 4) collect and analyze data 5) draw a conclusion. Hypothesis Data, Calculations Conclusions Follow up Questions Deliverables Resources/Materials

 Essential Question: What is a multimeter?

How is Voltage Measured?

1. 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.

2. 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.

3. 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.

4. 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

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

6. 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.

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

8. 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

 Essential Question: How are voltage, current and resistance related?

Ohm's Law

1. 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.

2. 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.

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

4. Measure currents using an ammeter.

5. State and explain Ohm's Law.
6. I = V / R

where:

I = current

V = voltage difference across the resistance

R = resistance

7. Solve problems with Ohm's Law.

8. 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

 Essential Question: Why are the watts listed on any electrical device?

Power

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

for electrical circuits: power = V(I)

2. State the unit for power. Watt = joule / sec
3. 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

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

5. 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.

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

7. Work circuit breaker problems.

8. 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.

 Essential Question: How can you best prepare for the test?

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

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