Exploring Circuits and Electrical Current: Essential Concepts and Experiments

Circuits
and Electrical Current
 
Essential Questions for Circuits
What are the requirements of a circuit?
What is actually going on in a working circuit?
What variable(s) affect what other variable(s)
in a circuit?  What law(s) and formulas govern
the relationship(s) between these variables?
What are the different kinds of circuits?  How
do they differ (design and use)?
Incandescent bulb:
 
How do you make a circuit?
You will be given one bulb, one battery and
more than enough wires.
Construct a sketch of how wires can be
connected to light a bulb.
Test your design.  If it doesn’t work, try
variations.
Record your working design(s)
Summarize the requirements of a functioning
circuit.
The Requirements of a Circuit
The Requirements of a Circuit
What do you already know?
The Basic Function of a Circuit
What is “really” happening in the
circuit?
Go onto Phet, Circuit Construction Kit (DC
Only)
Build a circuit with one bulb, one battery, one
switch, and just as many wires as you need to
make the circuit show you clearly what is
happening when the switch is closed.
What do the moving balls represent?  Which
way do they move?
What is “really” happening in the
circuit?
The balls represent electrons – obviously NOT
shown to scale.
The electrons move from negative on the
battery, around to positive.
Before scientists knew what moved, they
defined current as flowing from (the) positive
(terminal) to (the) negative (terminal).
A Useful Analogy
Sometimes, a closed conducting loop (circuit) is
compared to a water (amusement) park.
Complete this analogy:
  
Water Park
   
Circuit
  
pump
   
      
electrons
  
pipes
    
      
bulb
   
A Useful Analogy
Sometimes, a closed conducting loop (circuit) is
compared to a water (amusement) park.
Complete this analogy:
  
Water Park
   
Circuit
  
pump
   
battery
  
water
   
electrons
  
pipes
    
wires
  
slide/obstacles
  
bulb
 
Practice
Answer CYU #1,2 on PCR Lesson 2b.
Electric Potential Difference
What is it?
What are its units?
How do we measure it?
Is it “the cause” or “the effect” in a circuit?
Read 1b,c
Start your word web
Electric Potential Difference
Slang:  VOLTAGE
SI unit:  volt (V) named after 
Alessandro
Giuseppe Antonio Anastasio 
Volta
Measured with a voltmeter
Analogous to difference in height, if you want
to relate to gravity, or pressure in water pump
By CONVENTION, the positive side of a battery
is higher potential.
Electric Current
What is it?
What are its units?
How do we measure it?
What variables affect how much current
exists in an appliance?
Read 2c
Start your word web
Electric Current
The flow rate of charges
Unit:  ampere (amps, or just A)
 
1 ampere = 1coulomb of charge flowing thru a
conductor in 1 second
Measured with an ammeter
By convention, the “current” flows from positive
around to negative.
What Variable Affects what other
Variable(s) in a Circuit?
What is the mathematical relationship between
the ______________(_____) through a bulb and
the ______________(___) across the bulb in an
electrical circuit?
Circuit Schematics
What is the mathematical relationship
between the current(amps) 
thru
 one
bulb and the potential
difference(volts) 
across
 the bulb?
What is the mathematical relationship
between the current(amps) 
thru
 two
bulbs and the potential
difference(volts) 
across
 BOTH bulbs?
 
Understanding the Lab
What happened when potential difference
was doubled?
How did the results differ when a second bulb
was in the loop?
What do the bulbs do to the current?  (more
bulbs in series means ____ current)
Ohm’s “Law”:  I = 
V/R
The current in a circuit element (like a
bulb) is directly proportional to the
potential difference across the element,
and inversely proportional to the
resistance of the element
R: Resistance
R = 
V / I
R = 
L/A  (
=resistivity, L=length, A=cross
sectional area)  
Note:  Important in AP E&M
SI unit:  ohm (
)
Measured with an ohmmeter
All real conductors have a little of this,
insulators have a LOT of it.  An ideal
conductor has 0

and an ideal insulator has
Resistance
What is it?  (use The Lazy Mile at the water
park)
What happens in the circuit as the resistance
changes?
Example Problem
Ex:  A single loop circuit is made with a 1.5 volt
battery, and a light bulb.  An ammeter is used
to measure a 0.15A current in the loop.  What
is the resistance of the bulb in this circuit?
PCR Current Electricity 3c CYU 1-5, 7,8
(AP only) Checkpoint 3, plus…
…also rank them greatest to least according to:
 
-  current density
 
-  drift velocity
 
-  electric field (strength) in the conductor
Lab, Part II
Now, do the lab again, this time with a real
bulb, using real wires, and a “battery
eliminator.”   Only go up to 6.0V
 What is different when you graph your data?
 Why do you think it is different?
What happened to the brightness of the bulb as
you increased the potential difference through it?
What MEASUREMENT relates most closely to
brightness in the bulbs?
What measurement looks at…
How much charge flows thru a wire in a
second?
How the wire prevents the charges to flow?
The difference in energy (carried by each
charge) between two positions in a circuit?
The rate at which energy is transferred (or
WORK is done)?
Energy is…
The ability to do work
Measured in joules
Also measured in calories (1 cal = 4.18J)
Also measured in kilowatt x hours
(1kWhr = 3.6x10
6
J)
Something we will define more completely in
the last unit of the course
Power
The rate at which work is done / energy is
changed or transferred
Measured in watts (1watt = 1joule / 1 second)
Also measured in horsepower (1hp = 746W)
Also measured in kW (1kW = 1x10
3
W)
Measurements in a circuit
I:  Current (in amperes (A))
V:  Potential difference (in volts (V))
R:  Resistance (in ohms (
))
Power (in watts (W))
Equations
I=
V/R   
 
   
V = IR   
 
    R = 
V/I
P = I(
V)
  
P=I
2
R            P = (
V)
2
/R
Series Circuit
 
Series Circuits
All elements in a series circuit (or branch) have the
same__________________
If you add up the ________________in the elements
that are in a series circuit, the result is equal to the
_________________of the battery.
The power supplied by the battery equals the sum of
the power dissipated by all resistors.
In Series, R
eq
 = ?
Series Circuits
All elements in a series circuit (or branch) have the
same current
If you add up the potential differences in the elements
that are in a series circuit, the result is equal to the
potential difference of the battery.
The power supplied by the battery equals the sum of
the power dissipated by all resistors.
In Series, R
eq
 = R
1
 + R
2
 +…+R
n
Example
Draw a series circuit with a 3.0V battery, a 6
light bulb, and a 3
 light bulb.  Determine the
equivalent resistance of the circuit, the
current through each item in the circuit, the
potential difference across each item in the
circuit, the power supplied by the battery, and
the power “used” by each of the bulbs.
Series Circuits…
Charge is neither created nor destroyed, so the
__________ is the same for all parts of the
circuit.
Energy is neither created nor destroyed, so the
sum of the ______________ for all the bulbs
must equal the same measurement for the
battery.
Parallel Circuit
 
Parallel Circuits
All elements in a parallel circuit have the same
potential difference
If you add up the current in all the elements that are in
parallel, the result is equal to the current through the
battery.
The power supplied by the battery equals the power
dissipated by the resistors in total
In Parallel, 1/R
eq
 = 1/R
1
 + 1/R
2
 +…+1/R
n
Parallel Circuit
Draw a circuit with a 3.0V battery, a 6
 light
bulb, and a 3
 light bulb connected in
parallel.  Determine the equivalent resistance
of the circuit, the current through each item in
the circuit (that is three different
measurements), the potential difference
across each item in the circuit, the power
supplied by the battery, and the power “used”
by each of the bulbs.
Parallel Circuits…
Charge is neither created nor destroyed, so the
sum of the  __________ for all the bulbs is the
same as this measurement for the battery.
Energy is neither created nor destroyed, so the
sum of the ______________ for all the bulbs
must equal the same measurement for the
battery.
Each bulb has the same _________ as the
battery, because the wires connect each bulb to
the battery without any resistance (actually, with
negligible
 resistance).
Practice Problem
A 1.0
 and a 2.0
 light bulb are wired in
parallel, then connected to a 6.0V battery.
Determine the power supplied by the battery,
and dissipated by each bulb.  Which is
brightest?
Now, the bulbs are wired in series to the same
battery. Determine the power supplied by the
battery, and dissipated by each bulb.  Which is
brightest?
Is Physics Real?
Objective:  Determine if the statements made
about electric potential difference on slides 35 &
39 are true in actual circuits.
If measurements do not show these statements
are 100% accurate, why not?  Are the
statements false, or is something else (another
measurement) affecting the investigation.
Validating One Rule of Parallel and
Series Circuits
Reports:
 
- Objectives
 
- Circuit Diagram, labeled
 
- Data shown neatly
 
- Each statement, followed by the
 
measurement(s) and brief description(s)
 
that support, or refute the claim.  If the
 
claim is not (well) supported, explain why
 
you still believe it is true.
Now, we look at the “other”, relevant
measurement in electrical circuits…
 
What does the 60 watts mean for a
bulb?
A)  The bulb has 60 W and after that, it is used
up
B)  When turned on, the bulb uses 60 watts
regardless of the circuit it is in
C)  If the bulb is across a potential difference
of 120V, the bulb dissipates 60 J of energy
each second.
60W vs 120W
Determine the resistance of a “60W” bulb and
of a “120W” bulb.
Which draws more current?
What is the cost of running each for 2 hours?
What is a KILOWATT-HOUR?
A)  a unit of power
B)  a unit of electricity
C)  a unit of energy
D)  a unit of work
E)  a unit of current
F)  a unit of potential difference
G)  the amount of heat needed to warm 1.0
ml of water by one degree Celsius
A kWhr is….
(1000W) x (1hr)
(1000J/s) x (3600s)
3 600 000J
3.6 x 10
6 
J
3.6 MJ
The amount of electrical energy your parents pay about $0.20 for
Energy
SI unit:  
joule
 (J)
Other units:  calorie, kilocalorie, 
kilowatt-hour
E = P * 
t      (because a 
J
/
s
 * 
s
 = 
J
)
This is the physics measurement most closely
analogous to $$$  (1.0kWhr –or 3.6 
million
joules - of electrical energy costs about $0.25)
What does that 60W bulb cost to use
for two hours?
 (assuming $0.20 for each kWhr)
Save some $$$
A 20W CFL provides the same amount of light
as a conventional 75W bulb.  If the lamp you
wish to use is on for two hours a day, how
much will the CFL bulb save you in one year?
(use $0.20 per kWhr)
Apply what you have learned
1.
Build a series circuit with three bulbs.  
Gradually turn up the
potential difference applied across the circuit.
  Identify the
brightest and dimmest bulbs.
2.
Build a parallel circuit with three bulbs.  
Starting at 1.5V,
gradually turn up the potential difference applied across the
circuit.
  Identify the brightest and dimmest.
3.
Rank the bulbs by resistance – record on whiteboard.  You
MUST JUSTIFY your conclusion with facts about electrical
measurements in series and parallel circuits!  Compare your
results with other groups
4.
Repeat 
step 1
, but now use meters to measure current and
potential difference so you can compute the resistance of
each bulb.  You will use the handout to organize your
measurements, and perform calculations with an excel
document.  The excel document will also calculate energy
each bulb would use in one hour.  Were you correct in step
3?
AP Only Performance Assessment
Objective:  Determine the EMF and internal
resistance for two different D-cell batteries.
Report:
Title/Objective
Circuit Diagram
Data
Computations (4 steps)
Conclusion (be sure the numerical answers are
part of this!)
Slide Note
Embed
Share

Dive into the world of circuits and electrical current with a focus on understanding the requirements, components, and functioning of circuits. Explore essential questions, experiment with building circuits, and grasp the basics of how electricity flows through a circuit. Discover the different types of circuits and their design variations to deepen your knowledge in this foundational aspect of electrical engineering.


Uploaded on Sep 13, 2024 | 0 Views


Download Presentation

Please find below an Image/Link to download the presentation.

The content on the website is provided AS IS for your information and personal use only. It may not be sold, licensed, or shared on other websites without obtaining consent from the author. Download presentation by click this link. If you encounter any issues during the download, it is possible that the publisher has removed the file from their server.

E N D

Presentation Transcript


  1. Circuits and Electrical Current

  2. Essential Questions for Circuits What are the requirements of a circuit? What is actually going on in a working circuit? What variable(s) affect what other variable(s) in a circuit? What law(s) and formulas govern the relationship(s) between these variables? What are the different kinds of circuits? How do they differ (design and use)?

  3. Incandescent bulb:

  4. How do you make a circuit? You will be given one bulb, one battery and more than enough wires. Construct a sketch of how wires can be connected to light a bulb. Test your design. If it doesn t work, try variations. Record your working design(s) Summarize the requirements of a functioning circuit.

  5. The Requirements of a Circuit

  6. The Requirements of a Circuit

  7. What do you already know?

  8. The Basic Function of a Circuit

  9. What is really happening in the circuit? Go onto Phet, Circuit Construction Kit (DC Only) Build a circuit with one bulb, one battery, one switch, and just as many wires as you need to make the circuit show you clearly what is happening when the switch is closed. What do the moving balls represent? Which way do they move?

  10. What is really happening in the circuit? The balls represent electrons obviously NOT shown to scale. The electrons move from negative on the battery, around to positive. Before scientists knew what moved, they defined current as flowing from (the) positive (terminal) to (the) negative (terminal).

  11. A Useful Analogy Sometimes, a closed conducting loop (circuit) is compared to a water (amusement) park. Complete this analogy: Water Park pump Circuit electrons pipes bulb

  12. A Useful Analogy Sometimes, a closed conducting loop (circuit) is compared to a water (amusement) park. Complete this analogy: Water Park pump water pipes slide/obstacles Circuit battery electrons wires bulb

  13. Practice Answer CYU #1,2 on PCR Lesson 2b.

  14. Electric Potential Difference What is it? What are its units? How do we measure it? Is it the cause or the effect in a circuit? Read 1b,c Start your word web

  15. Electric Potential Difference Slang: VOLTAGE SI unit: volt (V) named after Alessandro Giuseppe Antonio Anastasio Volta Measured with a voltmeter Analogous to difference in height, if you want to relate to gravity, or pressure in water pump By CONVENTION, the positive side of a battery is higher potential.

  16. Electric Current What is it? What are its units? How do we measure it? What variables affect how much current exists in an appliance? Read 2c Start your word web

  17. Electric Current The flow rate of charges Unit: ampere (amps, or just A) 1 ampere = 1coulomb of charge flowing thru a conductor in 1 second Measured with an ammeter By convention, the current flows from positive around to negative.

  18. What Variable Affects what other Variable(s) in a Circuit? What is the mathematical relationship between the ______________(_____) through a bulb and the ______________(___) across the bulb in an electrical circuit?

  19. Circuit Schematics

  20. What is the mathematical relationship between the current(amps) thru one bulb and the potential difference(volts) across the bulb? What is the mathematical relationship between the current(amps) thru two bulbs and the potential difference(volts) across BOTH bulbs?

  21. Understanding the Lab What happened when potential difference was doubled? How did the results differ when a second bulb was in the loop? What do the bulbs do to the current? (more bulbs in series means ____ current)

  22. Ohms Law: I = V/R The current in a circuit element (like a bulb) is directly proportional to the potential difference across the element, and inversely proportional to the resistance of the element

  23. R: Resistance R = V / I R = L/A ( =resistivity, L=length, A=cross sectional area) Note: Important in AP E&M SI unit: ohm ( ) Measured with an ohmmeter All real conductors have a little of this, insulators have a LOT of it. An ideal conductor has 0 and an ideal insulator has

  24. Resistance What is it? (use The Lazy Mile at the water park) What happens in the circuit as the resistance changes?

  25. Example Problem Ex: A single loop circuit is made with a 1.5 volt battery, and a light bulb. An ammeter is used to measure a 0.15A current in the loop. What is the resistance of the bulb in this circuit? PCR Current Electricity 3c CYU 1-5, 7,8

  26. (AP only) Checkpoint 3, plus also rank them greatest to least according to: - current density - drift velocity - electric field (strength) in the conductor

  27. Lab, Part II Now, do the lab again, this time with a real bulb, using real wires, and a battery eliminator. Only go up to 6.0V What is different when you graph your data? Why do you think it is different? What happened to the brightness of the bulb as you increased the potential difference through it? What MEASUREMENT relates most closely to brightness in the bulbs?

  28. What measurement looks at How much charge flows thru a wire in a second? How the wire prevents the charges to flow? The difference in energy (carried by each charge) between two positions in a circuit? The rate at which energy is transferred (or WORK is done)?

  29. Energy is The ability to do work Measured in joules Also measured in calories (1 cal = 4.18J) Also measured in kilowatt x hours (1kWhr = 3.6x106J) Something we will define more completely in the last unit of the course

  30. Power The rate at which work is done / energy is changed or transferred Measured in watts (1watt = 1joule / 1 second) Also measured in horsepower (1hp = 746W) Also measured in kW (1kW = 1x103W)

  31. Measurements in a circuit I: Current (in amperes (A)) V: Potential difference (in volts (V)) R: Resistance (in ohms ( )) Power (in watts (W))

  32. Equations I= V/R V = IR R = V/I P = I( V) P=I2R P = ( V)2/R

  33. Series Circuit

  34. Series Circuits All elements in a series circuit (or branch) have the same__________________ If you add up the ________________in the elements that are in a series circuit, the result is equal to the _________________of the battery. The power supplied by the battery equals the sum of the power dissipated by all resistors. In Series, Req= ?

  35. Series Circuits All elements in a series circuit (or branch) have the same current If you add up the potential differences in the elements that are in a series circuit, the result is equal to the potential difference of the battery. The power supplied by the battery equals the sum of the power dissipated by all resistors. In Series, Req= R1+ R2+ +Rn

  36. Example Draw a series circuit with a 3.0V battery, a 6 light bulb, and a 3 light bulb. Determine the equivalent resistance of the circuit, the current through each item in the circuit, the potential difference across each item in the circuit, the power supplied by the battery, and the power used by each of the bulbs.

  37. Series Circuits Charge is neither created nor destroyed, so the __________ is the same for all parts of the circuit. Energy is neither created nor destroyed, so the sum of the ______________ for all the bulbs must equal the same measurement for the battery.

  38. Parallel Circuit

  39. Parallel Circuits All elements in a parallel circuit have the same potential difference If you add up the current in all the elements that are in parallel, the result is equal to the current through the battery. The power supplied by the battery equals the power dissipated by the resistors in total In Parallel, 1/Req= 1/R1+ 1/R2+ +1/Rn

  40. Parallel Circuit Draw a circuit with a 3.0V battery, a 6 light bulb, and a 3 light bulb connected in parallel. Determine the equivalent resistance of the circuit, the current through each item in the circuit (that is three different measurements), the potential difference across each item in the circuit, the power supplied by the battery, and the power used by each of the bulbs.

  41. Parallel Circuits Charge is neither created nor destroyed, so the sum of the __________ for all the bulbs is the same as this measurement for the battery. Energy is neither created nor destroyed, so the sum of the ______________ for all the bulbs must equal the same measurement for the battery. Each bulb has the same _________ as the battery, because the wires connect each bulb to the battery without any resistance (actually, with negligible resistance).

  42. Practice Problem A 1.0 and a 2.0 light bulb are wired in parallel, then connected to a 6.0V battery. Determine the power supplied by the battery, and dissipated by each bulb. Which is brightest? Now, the bulbs are wired in series to the same battery. Determine the power supplied by the battery, and dissipated by each bulb. Which is brightest?

  43. Is Physics Real? Objective: Determine if the statements made about electric potential difference on slides 35 & 39 are true in actual circuits. If measurements do not show these statements are 100% accurate, why not? Are the statements false, or is something else (another measurement) affecting the investigation.

  44. Validating One Rule of Parallel and Series Circuits Reports: - Objectives - Circuit Diagram, labeled - Data shown neatly - Each statement, followed by the measurement(s) and brief description(s) that support, or refute the claim. If the claim is not (well) supported, explain why you still believe it is true.

  45. Now, we look at the other, relevant measurement in electrical circuits

  46. What does the 60 watts mean for a bulb? A) The bulb has 60 W and after that, it is used up B) When turned on, the bulb uses 60 watts regardless of the circuit it is in C) If the bulb is across a potential difference of 120V, the bulb dissipates 60 J of energy each second.

  47. 60W vs 120W Determine the resistance of a 60W bulb and of a 120W bulb. Which draws more current? What is the cost of running each for 2 hours?

  48. What is a KILOWATT-HOUR? A) a unit of power B) a unit of electricity C) a unit of energy D) a unit of work E) a unit of current F) a unit of potential difference G) the amount of heat needed to warm 1.0 ml of water by one degree Celsius

  49. A kWhr is. (1000W) x (1hr) (1000J/s) x (3600s) 3 600 000J 3.6 x 106 J 3.6 MJ The amount of electrical energy your parents pay about $0.20 for

  50. Energy SI unit: joule (J) Other units: calorie, kilocalorie, kilowatt-hour E = P * t (because a J/s * s = J) This is the physics measurement most closely analogous to $$$ (1.0kWhr or 3.6 million joules - of electrical energy costs about $0.25)

Related


More Related Content

giItT1WQy@!-/#giItT1WQy@!-/#giItT1WQy@!-/#giItT1WQy@!-/#giItT1WQy@!-/#giItT1WQy@!-/#giItT1WQy@!-/#giItT1WQy@!-/#