Wednesday, January 19, 2011

Hello everybody! Today's class consisted of answering the three worksheets we received the previous day, so I'll go ahead and post up the answers!


Transparency 25-2 Worksheet
" AC Generator"

1. As a wire moves through position 1, how is it moved with respect to the magnetic field?
- The wire is moving perpendicular to the field.

2. How much current is carried through the wires as it moves through position 1?
- Max amount of current, Imax.

3. As the wire reaches position 2, how is it moving with respect to the magnetic field?
- The wire is moving parallel to the field.

4. How is the change is the orientation of the wire in the magnetic field related to the amount of current induced in the wire?
- Only the component of motion that is perpendicular to the field induces a current.
Position 1 & 3 - Max I (current)
Position 2 & 4 - zilch

5. How much current is carried through the wire as it moves through position 3?
- Imax.


Transparency 25-3 Worksheet
"Lenz's Law"

1. What is the direction of the current induced in the wire as a result of moving through the magnetic field? What rule is used to determine this direction?
- Induced current ia downwards, using the 3rd right hand rule.

2. How does the direction of the force exerted by the magnetic field on the wire related to the original motion of the wire?
- Force exerted by B opposes original motion of wire.

3. What is Lenz's law?
- It states that the direction of the induced current is such that the magnetic field resulting from the induced current opposes the change in the field that caused the induced current.

4. If the generator produces a small current, will the armature be easy or hard to turn? Why?
- Easy to turn, the opposing force on the armature is small.

5. Why does placing a mechanical load on a motor cause more current to be carried through the motor?
- The rotation of the motor slows. The slowing decreases back EMF and allows more current to be carried through the motor.


Transparency 25-4 Worksheet
"Step-Up and Step-Down Transformers"

1. In the step-up transformer, the primary coil has two turns, and the secondary coil has four turns. By what factor is the voltage in the primary circuit stepped up by the transformer?
- Vp/Vs = Np/Ns = 2/4 = 1/2
2Vp/Vs = 1/2
Doubles Vp

2. If the voltage across the primary circuit of the step-up transformer were 120 V, what would be the voltage across the secondary circuit?
- Vs = Vp.Ns/Np = (120 V)(4 turns)/(2 turns
Vs = 240 V

3. If the voltage across the primary circuit of the step-down transformer were 350 V, what would be the voltage across the secondary circuit?
- By not knowing the number of turns on the primary or secondary, you cannot calculate Vs.

4. If the current in the primary circuit of the step-down transformer were 40 A, what would be the current in the secondary circuit?
- Increase I (current) on the secondary circuit, but can't calculate accurately due to not knowing both voltages.

5. If the voltage in a transformer is stepped up, the current has been stepped down. Ohm's law indicates that increase voltage typically produces increased current. Explain this seeming contradiction.
- Ohm's law holds true in a single circuit. In this instances, the current being compared are actually in two different circuits.


Chapter 37: Electromagnetic Induction
"Transformers"

1. What will be the voltage output of the secondary?
- 1200 V

Vs = Vp.Ns/Np

2. What current flows in the secondary circuit?
- 1.2 A

Is = Vs/R

3. Now that you know the voltage and the current, what is the power in the secondary coil?
- 1440 W

Ps = Is.Vs

4. Neglecting small heating losses, and knowing that energy is conserved, what is the power in the primary coil?
- 1440 w

5. Now that you know the power and the voltage across the primary coil, what is the current drawn by the primary coil?
- 12 A

Ip = Pp/Vp

6. (up)(down)
7. (more)(less)
8. (voltage)(energy and power)
9. (step-down)(20/1)
10. (ac)(continually change)

Finally, filling out the last of our chapter 25 Study Guide!

Self-Inductance

Current generates a(n) magnet field, creating new field lines, which cut through the wires. As a result, and EMF is generated and it opposes the current change. The faster you try to change the current, the larger the opposing EMF, and the slower the current change. Because of this self-inductance, work has to be done to increase the current that flows, and the energy is stored in the magnetic field.

Transformers

A transformer is used to increase or decrease AC voltage without a loss of energy. A transformer contains two coils that are insulated electrically from each other, but that share the same core. When the primary coil is connected to a source of AC voltage, the changing current creates a varying magnet field. A varying current is induced in the secondary coil, by the process of mutual inductance. The ratio of primary and secondary voltages depends on the ratio of the number of turns in the two coils. I a step-up transformer, the primary voltage is less than the secondary voltage, and the current in the primary circuit is greater than the current in the secondary. In a step-down transformer, the primary voltage is the secondary voltage and the current in the primary circuit isgreater than less than the current in the secondary circuit.

Now after all that we received 3 more pages!

Chapter 26 Review
Transparency 22-4 "Electric Power Transmission"

And last but not least THE EXAM REVIEW ANSWER KEY!

Don't forget to pick those up and FAST! Especially the Answer Key. I'll upload that as soon as I can. (Too lazy to change computers.)

Less than, but about, 2 more weeks until exams! Studystudystudy, and an expected test (our last!) on Tuesday. Good luck everyone!

Tuesday, January 18, 2011

Hello my fellow classmates. I am back to compensate for yesterday's scribe. During yesterday's lesson, we had watched a video on electromagnetic induction and alternating current. Along with that video, we were given questions to answer while watching the tape. I will attach a link to the question sheet and the answers to it at the end of this post. After watching the video, we were given 3 other hand-outs called "Transparency 25-3," "Transparency 25-4," and "Transformers." If you missed those hand-outs, please see Ms. Kozoriz for them.

We also discussed about some interesting news about our province has been selling hydro to the U.S.A. This connects to the topic of Alternating Currents (AC) where it can be transported over large distances/areas. Our province has been earning a large amount of profit from selling hydro to America.

Anyways, here is the video question sheet for those of you who didn't receive a copy.

ELECTROMAGNETIC INDUCTION/ALTERNATING CURRENT VIDEO WORKSHEET:

Here are the answers for the questions:

ELECTROMAGNETIC INDUCTION:

1.) A flow of current for a magnetic field

2.) Hans Christian

3.) Michael Faraday

4.) No

5.) First electric motor

6.) When there is a change in the magnetic fields

7.) F = Bqv (F = Force, B = Magnetic field, q = charge, v = velocity)

8.) Loop moves away from current, loop moves towards current, magnet moves away from current, magnet moves towards current

9.) Yes

10.) Number of field lines per area

11.) Zero

12.) Phi

13.) Yes

14.) Yes

15.) Current induced creates a magnetic field of it's own

16.) Yes

17.) Change the magnetic flux

18.) Electricity and magnetism

ALTERNATING CURRENT:

1.) Emigrated from Eastern Europe, he knew 12 languages

2.) Moving back and forth

3.) Alternating current

4.) Direct current, Thomas Edison

5.) He invented the phonograph, motion picture camera, and telegraph

6.) AC can be transported over large distances

7.) A small current, large voltage

8.) Using transformer to send power to large distances

9.) Raises and lowers voltage

10.) Yes

11.) Heat, distance, current small, voltage high (I^2 x R OR P^2 x R/V^2)

12.) Generators are needed for far distances

13.) Edison didn't like Tesla

For those of you who missed some of the answers, here you are :)!!! If there are any mistakes, please correct it by leaving a comment. If you are unsure about the answer, please see Ms. Kozoriz.

As for the whole class, not much was taught yesterday. For those who were absent, you didn't miss anything important. Remember to study for our physics exam that is in 13 days!!! Our next test will be on Monday, January 24, 2011. So get ready to do some studying!!! Thanks for reading my post :), hope you all have a great night!!!

Monday, January 17, 2011

We started today's class by going over last week's homework, Transparency 25-1 and Electromagnetic Induction.

For Transparency 25-1 Worksheet, the answers are:
1. Electrical energy; battery
2. Rod with a wire coiled around it; magnetic force created by the field magnet
3. N and S poles will reverse
4. Mechanical energy from the crank
5. Electromagnetic induction as the wire moves through the magnetic field
6. EMF increases

For Electromagnetic Induction, the answers are:
1) 0.97 V
2) 1.9 x 10^-3 V
3) 0.020 V
4) 1.0 x 10^-4 V
5) 3.74 V
6) 50 turns
7) 1.8 V

Later on in the class, we also went over Lenz's Law on the Chapter 25 Study Guide. The answers for this are:
- direction
- flux
- current
- armature
- increases
- back-EMF
- decreases
- decreases

Lastly, we received a couple of handouts; Induced EMF/Factors Affecting Induced EMF, a graph of induced potential difference vs time, Lenz's Law, a worksheet to practice Lenz's law and Transparency 25-2.

Please have the worksheet for Lenz's law and Transparency 25-2 done for homework.

-- Rainer

Wednesday, January 12, 2011

Hey grade 12's!

Today we went over the duck textbook questions, we were assigned on Friday when Ms. K. was away. The questions that were assigned were 35. a) - d) 36, and 37 on pages 622 - 623. We also went over the worksheet that was handed out to us on Monday called Combination Circuits. The rest of the class was used to finish our Circuit Booklet Assignment or work on the physics exam review or study for the test.

TEST TOMORROW, GOOD LUCK!

MONDAY, JANUARY 10, 2011

MONDAY : JANUARY 10 , 2011

Today, we started off the class with Ms. Kozoriz handing out our test corrections and some work assignments that we gave in awhile ago.

We also got our EXAM REVIEW BOOKLET too, so those who were not in class today, make sure you get them soon to start studying!

Next, the Electric Circuit booklet that we were supposed to make as a "self-review" for our exams were due today and asked to be handed in. If you were not able to complete and hand it in today's class, please finish and hand it in as soon as possible for tomorrow's morning.

We went over the corrected Compound Circuits 4) d. question that we were supposed to hand in on Friday's class.

After that, Ms. Kozoriz let us watch this video on Electric Currents and we were supposed to jot down 5-6 points and hand them in by the end of the class. This video was like a review, and for those who didn't finish/start on their Electric Circuit booklet, it could've had some important key points to help you with it.

After the video, Ms. Kozoriz gave us a new worksheet to work on called Combination Circuits.

Again, if you were not in class today, please make you sure you will get the hand-out from her!

Then we had the rest of the class time to work on our Electric Circuit booklet, the Combination Circuits worksheet and review for our TEST on Thursday, January 13.

REMEMBER TO STUDY FOR YOUR TEST ON

THURSDAY, JANUARY 13,

ON ELECTRIC CURRENTS!

REMINDER THAT OUR EXAM IS EXACTLY 3 WEEKS FROM TOMORROW!

Thanks for reading, hope this helped! Have a great night (:

Friday January 7th, 2011

During Friday's class, Ms. Kozoriz was absent and we had a substitute. We were assigned pg.622-623 in the Physics textbook. Questions #35a, #35b, #35c, #35d, #36, #37a and #37b were due for Monday. Also due Monday was the assignment to make a small booklet on Electric Circuits. "Compound Circuits" #4d was due on Friday's class.

Series, Parallel and Compound Circuit

Hiii everyone,  today we started with Study Guide and went through following answers:

1.b
2.c
3.d
4.a
5.a
6.b
7.b
8. charges conserved
9.Vb=IRb
Vb=(VRb/Ra+Rb)
10. series circuit
11. gives proper amount of voltage
      we dont need to worry about 12 and 13.
14.b
15.c
16.b
17.a
18.a
Applications of circuits:-
1. true
2. false
3. false
4. true
5. false
6. false
7. a
11. ammeter
12. series
13. low
14. voltmeter
15. parallel
16. high
    We got worksheet about compound circuits.
1. R= 2.5
2. R= 4
3. R=1
4.a) Resistance= 2
P=I.V=8w
Resistance=4
P=16w
Resistance=6
P=24w
b) Resistance=1
P=4w
Resistance=2
P=8w
c) Resistance=6
P=6w
Resistance=3
P=12w
      Question 4(d) is homework which is due for tomorrow. We also worked on worksheet Series and Parallel Elements and we have an assignment on three circuits which is due on Monday 01/10/11.