Name Class Date given Date due

Chapter 19 & 20: CircuitsStudent Expectations/Self assessment

PHYS 5: know changes occur within a physical system and recognizes that energy and momentum are conserved I can: Define current, voltage, resistance, resistivity, identify these quantities by their units and apply these concepts to analyze

both simple and complex circuitso Ex. What are the units for current, voltage and resistance? Give a proper formula to express

the relationship between them.o Initial understanding Final understanding

Understand and apply the meaning of “closed circuit” to solve simple circuit problemso Ex. When is a circuit considered “closed”?o Initial understanding Final understanding

Apply Ohm’s Law to analyze series, parallel, and combo circuitso Ex. What is the voltage of a battery if it has 15 ohms of resistance when a current of 10mA is

applied?o Initial understanding Final understanding

Distinguish between series and parallel circuits, their uses and weaknesseso Ex. How do some strands of Christmas bulbs stay lit, even when one goes out?o Initial understanding Final understanding

Describe the behavior of current, resistance, and voltages in series and parallel circuitso Ex. How is resistance affected by elements being in a series instead of parallel?o Initial understanding Final understanding

Distinguish between and calculate electric power and electric energy with proper unitso Ex. How much power is used by a 35Ω resistor when connected to a 120V circuit?o Initial understanding Final understanding

Chapter 19&20 Circuits assignments. Please check grade book for due dates.CASTLE Section 1 CASTLE Section 2CASTLE Section 3 p695 # 1 – 5p703 # 1 – 5 p710 # 1 – 4p712 #1-2 p739 #2, 4 – 6p744 #2 – 4 test

This unit will alternate with a series of electrifying activities called CASTLE activities. (Capacitor Aided System for Teaching and Learning Electricity) Almost all these activities will be on T/Th and you will be in set groups as follows.

8th period: 1 Red – Raymond, Alex, Adam 2 Orange – Cameron, Zach, Ty 3 Yellow – David, Brian, Holly 4 Green – Micaela, Madyson, Heather, Tess 5 Blue – Josh, Bill, Amber W. 6 Purple – Johnny, Amber B., Leandra

9th period: 1 Red – Jed, Z, Brandynne 2 Orange – Derrick K, Justin 3 Yellow – Ted, Hunter 4 Green - Dorvionne, Anthony, Derek W.

M/W classes will be for lessons.

Ch 19 & 20 CircuitsNew variables! Yay!

Variable Name Unit What it is

I electric current

amperes (A) the rate of how much electricity is moving through at once

ΔQ charge Coulombs (C) charge moving through an area

Δt time second (s) Time from start to finish

R resistance ohms (Ω) how much something resists letting current through

ΔV potential difference aka, voltage

volts (V) the ability to do work based on the difference between charges

P electric power

watts (W) rate at which current is changed to potential difference

Traffic jam experiment

Questions:1. Which situation represented the largest current, I?2. Which situation represented the largest resistance, R?3. Which situation is capable of the most power, P?4. Which situation would take the least amount of time to move equal current?

More about each term:ELECTRICITY, n.The power that causes all natural phenomena not known to be caused by something else.(Ambrose Bierce, The Devil's Dictionary, 1911)

In common English the word “electricity” can refer to several different things.

Moving electricity (electrodynamic electricity, like in your house wiring) is not exactly like static electricity. Static electricity is electrons actually relocating from one place to another. Electrodynamic electricity is NOT really the movement of electrons but is the movement of an electric field that is passed from one electron to another as a wave and the energy in the vibrations of those electrons. This field is generally considered to be positive.

Electrons do move a little bit, called drift velocity, but it’s very slow. It would take an electron in a 10A current 68 minutes to move 1 meter. Do electrons move in the same direction as the electric field or the opposite?

So why do lights come on the instant you flip a switch?

I – electric current; measured in amperes (A); the rate of how much charge (electricity) is moving through at once.

AC/DC – not just a band!

DC – direct current moves from one end to another. Batteries have fixed positive and negative ends. What happens when you switch the batteries around in a flashlight?

AC – alternating current, the direction the charge flows switches. In between each switch, the lights actually go off. Why don’t we see the lights flicker?

60 Hz

Current will make more sense when we’ve finished the CASTLE labs.

ΔQ – charge moving through an area; measured in Columbs (C)

Charge is a measure of the amount of electrical energy

Δt – time, measured in second (s)

R – resistance; measured in ohms (Ω); how hard it is to move current through

A resistor is something that resists letting current flow through. It’s like putting your thumb over the end of a water hose. Some examples of resistors are:

Sometimes resistors are used just to reduce the current in a wire. These resistors have different colored bands, like a numbering code, telling you how resistive it is.

Salt and water can both lower the resistance of your body to electricity. Combined, saltwater can lower your resistance from about 500,000Ω down to about 100Ω. How do lie detectors work?

GSR

You can put strings of resistors together end to end, called in series, or next to each other, called parallel. More on that later.

ΔV – potential difference (aka, voltage); measured in volts (V); the ability to do work based on the difference between charges at one location compared to the charge at another location. Usually measured from one side of something, like a light bulb or a battery, to the other side. Which can unleash more energy in the same amount of time, a 1.5m waterfall or a 9m waterfall?

Which has a greater difference between ends, a 9V battery or a 1.5V D battery?

Which can release more energy in the same amount of time, a 9V battery or a 1.5V D battery?

P – electric power; measured in watts (W); the rate at which current, C, is changed to potential difference, ΔV.

Which has more resistance, a 40W bulb or a 100W bulb?

Which one converts energy from an electrical form to a different form of energy the fastest?

Electric companies sell energy, not power. Your electric bill is measured in kilowatts hour, kw x hr.

1kWhr = 3.6 x 106 Joules of energy

New Equations! Yay!Remember: m (milli) = 10-3, µ (micro) = 10-6, p (picco) = 10-9

Electric current: I = ΔQ I – Δt Q –

Resistance: R = ΔV R – I V –

I –

Can be rewritten as Ohm’s Law (sort of): ΔV = IR

Electric Power: P = IΔV P – I – V –

P = (ΔV) 2 R – R

Practice:1. While working in the lab, you need more light from a bulb. List all the ways you could

increase the current in the bulb filament.

2. The charge going through a filament is 3.0C in 5.0s. What is the current in the filament?

3. How many electrons pass through the filament during 1 minute?

4. You’re drying your hair with a 9.1A hairdryer. How long does it take for 1.9x103C of charge to go through the dryer?

5. You are MacGyver. You are creating a detonator to release an angry rhino from an enclosed parking lot you are parked in. You must decrease the current in a wire to successfully create the detonator or your car will be stampeded by said rhino and then blow up. But you only have one type of wire. What do you do?

6. How much current is used by a toaster with 10.2 resistance when plugged into a 120V socket?

7. An ammeter registers a current of 2.5 in a wire when connected to a 9 volt battery. What is the resistance of the wire?

8. If the resistance of a light bulb is increased, how will the electrical energy used by the bulb over the same amount of time change?

9. The potential difference across a resting neuron in your body is about 70mV. The current is about 200µA. How much power does the neuron release?

10.A computer is connected across a 110V power supply. The computer dissipates 130W of power in the form of electromagnetic radiation and heat. Calculate the resistance of the computer.

11.What does it cost to watch the World Series (21 hours) on a 90W black and white TV if energy is $0.07kWh?

HW p695 # 1 – 5

HW p703 # 1 – 5

HW p710 # 1 – 4 p712 #1-2

New pictures! Yay!

Closed circuit – electricity can flow from one point, all the way around and back to the starting point.

Open circuit – there is a break at any point along the path.

emf - source of potential difference. Examples are

12.Which symbol(s) represents something that stores energy?

13.Which symbol(s) represents something that transmits energy?

14.Which symbol(s) represents something that changes energy?

15.How can birds sit on a wire?

16.When current stronger than 10mA goes through a person the muscles automatically contract. If the person is holding a live wire, how can you pry his hand off the wire without electrocuting yourself?

17.Identify which of the schematic diagrams below will have a current and which will not.a. b.

c. d.

18.Identify all the types of elements in schematic diagrams 10a and 10b above.

And a few more equations! Yay!

Remember: when you take the inverse of a variable, it goes under 1 and becomes negative. Ex the inverse of R is 1/-R.

Series Parallel

Resisters in series equation: Req = R1 + R2 + R3… Resisters in parallel equation:

Current in series equation: I = I1 = I2 = I3 … Current in parallel equation: I = I1 + I2 + I3…

Potential difference series: ΔV = ΔV1 + ΔV2 … Potential difference parallel: ΔV = ΔV1 = ΔV2 …

Practice:

19.A 9.0V battery is connected to four light bulbs as shown below. Find the equivalent resistance for the circuit and the current in the circuit.

2.0 Ω 4.0 Ω 5.0 Ω 7.0 Ω

9V

20.What is the current in each resistor?

21.A 9.0V battery is connected to four resisters, as shown below. Find the equivalent resistance for the circuit and the total current in the circuit.

2.0 Ω 4.0 Ω 5.0 Ω 7.0 Ω

22. What is the potential difference across each resistor?

23.A house has a toaster, a microwave, and a popcorn popper in parallel to each other and an overhead light in series with the other three items all on a single 120V circuit. Draw a schematic diagram using of the circuit.

24.When will the appliances in parallel work right?

HW p739 #2, 4 – 6 p744 #2 – 4

25.When will the light work at full power?

According to William J. Beaty, Electrical Engineer -Do generators make electricity? To answer this question, consider the household light bulb. Inside a lamp cord the charges (the electrons) sit in one place and wiggle back and forth. That's AC or alternating current. At the same time, the waves of electromagnetic field move rapidly forward. This wave-energy does not wiggle, instead it races along the wires as it flows from the distant generators and into the light bulb. OK, now ask yourself this: when "electricity" is flowing, is it called an Electric Current? Yes? If so, then electricity is charge. And therefore we must say that the "electricity" sits inside the wires and vibrates back and forth. Generators do not create it, and it does not flow forward. Next, ask yourself if electricity is a form of energy. If it's energy, then electricity is made of electromagnetic fields, and it doesn't wiggle back and forth within the wires. Generators do create it, and it races along the wires at high speed. But electricity cannot do both! Which one is really "the electricity?" Is it the wiggling electrons, or is it the high-speed EM field energy? The experts cannot agree on a single definition. The reference books give conflicting answers, so there *is* no answer. (from http://amasci.com/miscon/whatis.html)