Physics Packet Electricity Complete E.C Stamps

1. Sum 34.2-5,11,Q4-14,23-25

2. Electric circuit Notes

3. Lab: 2 colored pages

4. Circuits Wkst side 1

5. Practice Written Ex side 2

6. Sum 33.1-2,Q1-7

7. Sum 36.2&5,Q3, 10,11 Diagrams 36.2 and 36.5

8. Diagrams 37.3 & 8

9. Study Guide

0 / 10 / 20 +

Total = ___________

+Parent Signature __________________

CONCEPTUAL PHYSICS

Chapter 34 Electric Current 151

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34-1Concept-DevelopmentPractice Page

Electric Current

1. Water doesn’t fl ow in the pipe when (a) both ends are at the same level. Another way of saying this is that water will not fl ow in the pipe when both ends have the same potential energy (PE). Similarly, charge will not fl ow in a conductor if both ends of the conductor are at the same electric potential. But tip the water pipe and increase the PE of one side so there is a difference in PE across the ends of the pipe, as in (b), and water will fl ow. Similarly, increase the electric potential of one end of an electric conductor so there is a potential difference across the ends, and charge will fl ow.

a. The units of electric potential difference are

(volts) (amperes) (ohms) (watts).

b. It is common to call electric potential difference

(voltage) (amperage) (wattage).

c. The fl ow of electric charge is called electric

(voltage) (current) (power),

and is measured in

(volts) (amperes) (ohms) (watts).

2. Complete the statements.

a. A current of 1 ampere is a fl ow of charge at the rate of coulomb per second.

b. When a charge of 15 C fl ows through any area in a circuit each second, the current is A.

c. One volt is the potential difference between two points if 1 joule of energy is needed to move

coulomb of charge between the two points.

d. When a lamp is plugged into a 120-V socket, each coulomb of charge that fl ows in the current is

raised to a potential energy of joules.

e. Which offers more resistance to water fl ow, a wide pipe or a narrow pipe?

Similarly, which offers more resistance to the fl ow of charge, a thick wire or a thin wire?

CONCEPTUAL PHYSICS

152 Chapter 34 Electric Current

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Ohm’s Law

1. How much current fl ows in a 1000-ohm resistor when 1.5 volts are impressed across it?

2. If the fi lament resistance in an automobile headlamp is 3 ohms, how many amps does it draw when connected to a 12-volt battery?

3. The resistance of the side lights on an automobile are 10 ohms. How much current fl ows in them when connected to 12 volts?

4. What is the current in the 30-ohm heating coil of a coffee maker that operates on a 120-volt circuit?

5. During a lie detector test, a voltage of 6 V is impressed across two fi ngers. When a certain question is asked, the resistance between the fi ngers drops from 400,000 ohms to 200,000 ohms. What is the current (a) initially through the fi ngers, and (b) when the resistance between them drops?

(a) (b)

6. How much resistance allows an impressed voltage of 6 V to produce a current of 0.006 A?

7. What is the resistance of a clothes iron that draws a current of 12 A at 120 V?

8. What is the voltage across a 100-ohm circuit element that draws a current of 1 A?

9. What voltage will produce 3 A through a 15-ohm resistor?

10. The current in an incandescent lamp is 0.5 A when connected to a 120-V circuit, and 0.2 A when connected to a 10-V source. Does the resistance of the lamp change in these cases? Explain your answer and defend it with numerical values.

CONCEPTUAL PHYSICS

Chapter 34 Electric Current 153

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1. What is the power when a voltage of 120 V drives a 2-A current through a device?

2. What is the current when a 60-W lamp is connected to 120 V?

3. How much current does a 100-W lamp draw when connected to 120 V?

Electric Power

Recall that the rate energy is converted from one form to another is power.

power = energy converted

= voltage × charge

= voltage × charge

= voltage × currenttime time time

The unit of power is the watt (or kilowatt). So in units form,

Electric power (watts) = current (amperes) × voltage (volts),

where 1 watt = 1 ampere × 1 volt.

34-2Concept-DevelopmentPractice Page

4. If part of an electric circuit dissipates energy at 6 W when it draws a current of 3 A, what voltage is impressed across it?

5. The equation power = energy converted

time

rearranged gives energy converted =

6. Explain the difference between a kilowatt and a kilowatt-hour.

7. One deterrent to burglary is to leave your front porch light on all the time. If your fi xture contains a 60-W bulb at 120 V, and your local power utility sells energy at 8 cents per kilowatt-hour, how much will it cost to leave the bulb on for the whole month? Show your work on the other side of this page.

Name ___________________________ Class __________________ Date ____________

Chapter 34 Electric Current©

Pearson Education, Inc., or its affiliate(s). All rights reserved.

294 Conceptual Physics Reading and Study Workbook Chapter 34

Calculating PowerIf four 1.5-V batteries deliver 1.25-A current to a small motor, what is thepower provided to the motor?

1. Read and Understand

What information are you given?voltage = V = 4 1.5 V = 6.0 V

current = I = 1.25 A

2. Plan and Solve

What unknown are you trying to calculate?power = P = ?

What mathematical expression can you use to calculate the unknown?P = VI

P = (6.0 V)(1.25 A) = 7.5 W

3. Look Back and Check

Is your answer reasonable? Yes, the number calculated is a product of current and voltage and the

units indicate power.

Math Practice

On a separate sheet of paper, solve the following problems.

1. An 8.0-V power supply delivers a 1.75-A current to a circuit. Calculatethe power provided to the circuit.

2. How much power is used by a set of lights operating on a 12-V batteryand 2.75 A?

3. A 15-W motor draws a current of 1.25 A. What is the voltage impressedacross the circuit?

Electricity Lab Rules

Every group member must know how to use the multimeter with the wiring and resistors and batteries for the exam!!!1.

You MUST use the SAME BOX each day of the lab.2.

Write your Lab group/Box Number on page 1 of your worksheet.3.

You MUST know how the "wiring diagrams" go with the actual wiring set-ups in order to understand this unit!4.

Make sure all your materials get replaced into the correct box (your box) at the end of the lab period.5.

The Multimeter measures three things:

Resistance (R)1.

Volts (V)2.

Current (I) - CAUTION3.

Multimeters can be broken...

Only one way to break them, so pay attention:

Checking the "CURRENT" (I) of a battery by itself will blow the fuse in the multimeter and it will have to be replaced.1.

Only one way to not break it when measuring CURRENT:

There MUST be a RESISTOR (R) between the battery and the multimeter when you test for CURRENT.1.

Remember the RESISTOR as a PROTECTOR for the multimeter. It cannot handle all the current of a battery all by itself, itneeds the resistor to protect it.

Battery-Resistor-Current=Good

Battery-Current=BAD

End Page 3 - Begin Page 4

Circuits Practice Worksheet name __________________________ per.____

PV

= = = AIVW

P IV12,000,000 W =

WV

=

= =

I

I

× 120 V

A

CONCEPTUAL PHYSICS

Chapter 37 Electromagnetic Induction 165

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Power Transmission

Many power companies provide power to cities that are far from the generators. Consider a city of 100,000 persons who each continually use 120 W of power (equivalent to the operation of two 60-W light bulbs per person). The power constantly consumed is 100,000 persons × 120 W / 1 person = 12 million W (12 MW).

1. What current corresponds to this amount of power at the common 120 V used by consumers?

This is an enormous current, more than can be carried in the thickest of wires without overheating. More power would be dissipated in the form of heat than would reach the faraway city. Fortunately the important quantity is IV and not I alone. Power companies transmit power over long distances at very high voltages so that the current in the wires is low and heating of the power lines is minimized.

2. If the 12 MW of power is transmitted at 120,000 V, the current in the wires is

This amount of current can be carried in long-distance power lines with only small power losses due to heating (normally less than 1%). But the corresponding high voltages wired to houses would be very dangerous. So step-down transformers are used in the city.

3. What ratio of primary turns to secondary turns should be on a transformer to step 120,000 V down

to 2400 V?

4. What ratio of primary turns to secondary turns should be on a transformer to step 2400 V down to

120 V used in household circuits?

5. What is the main benefi t of AC compared to DC power?

37-2Concept-DevelopmentPractice Page

PE

PE = mgh

m = (9.8 m/s2)(10 m)

J = kg=

mgh

mgh

Energy = power × time = 100 W × 1 yr × ×1 J/s1 W

365 d1 yr

× 24 h1 d

× 3600 s1 h

= J

kg = kg5 ×

Lkg

1 m3

1000 Lkg × 1 m3× = Volume =

m3

m3/poolful≈ poolfulsNumber of poolfuls =

CONCEPTUAL PHYSICS

166 Chapter 37 Electromagnetic Induction

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Power Production

Does it take a lot of water to light a light bulb? That depends on its wattage and how long it glows. In this practice page, you are to calculate the mass and volume of water that falls over a 10-m high dam to keep a 100-W light bulb glowing for 1 year.

1. First, calculate how many joules are required to keep the bulb lit for 1 year.

2. What mass of water elevated 10 m has this much PE? From Chapter 9, recall that gravitational PE = mgh:

3. But this assumes 100% effi ciency. A hydroelectric plant is typically 20% effi cient. This means only 1 part in 5 of the PE of the falling water ends up as electricity. So the mass above must be multiplied by 5 to get the actual amount of water that must fall to keep the 100-W bulb lit.

4. This is an impressive number of kilograms! To visualize this amount of water, convert it to cubic meters. (Recall 1 kg of water occupies 1 liter, and there are 1000 liters in 1 cubic meter.)

5. For comparison, an Olympic-size swimming pool holds about 4000 m3 of water. How many such poolfuls of water are required to keep a 100-W bulb lit for one year?

Does it take a lot of water to light a light bulb? To light a city full of light bulbs? Now you have a better idea!

Name:______________________per._______

Conceptual Physics Study Guide – Electricity & Fields (Ch 32-37) 1. What does “action at a distance mean? 2. Draw an electric field with a positive and negative charge and arrows:

a. What do the arrows represent? 3. What happens if a. two electrons are held close together b. two protons are held close together c.

an electron and a proton are held close together? 4. What is an electrical potential?

5. What is a volt?

6. Name two sources of electrical potential:

7. What is current?

8. What is resistance?

9. What is power?

10. what is ohm’s law?

11. What is the equation for power?

12. What is a circuit?

13. What flows through a circuit?

14. When resistors are in series, what is the same at each resistor?

a. What adds up to what?

b. How can you find the total resistance?

15. When resistors are in parallel, what is the same at each resistor?

a. What adds up to what?

16. What is the purpose of a fuse? 17. Every charged particle possesses what (field)?

18. Moving electrons produce what (field)?

19. Why/how can a magnet push against a non-magnetic wire like copper?

20. Why are wires formed into multiple loops in motors and generators instead of a single straight

wire? 21. What happens when a magnet is moved back and forth near a wire?

22. In a generator why does the magnet stay still and the wire move around in circles (think of a real

practical answer, not scientific, it just makes sense)? 23. What is the basic difference between a motor and a generator?

24. A charged battery has two sides to it, a _________ potential side and a __________ potential side.

And the _____________ physically move from _________ to _________ until the battery is “dead” (which means that the two sides are now _________________ potential.

25. What is induction?

26. What is Faraday’s Law?

***Go Online to Mr. Morrison’s website and complete the Practice Exam. Your name, ID number and test results will be sent by email to Mr. Morrison in order to get credit for this exam!!!***