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Transcript
Name
Class
Date given
Date due
Electrodynamics/Circuits
Chapter 19&20 Circuits assignments.
CASTLE Assignment 1
CASTLE Assignment 2
CASTLE Assignment 3
Please check grade book for due dates.
HW Electric Power & Energy
HW Circuits Around the World
HW Electric Circuits – Series & Parallel
New variables! Yay!
Name
Variable Unit
What it is
electric
current .
I
amperes (A) .
the rate of how much electricity is moving through at once . I =
ΔQ/Δt
charge
ΔQ
Coulombs (C)
time
Δt
seconds (s)
Electrical energy/charge moving through an area. (Notice the
capital Q. How is this different from ‘q’?)
Time from start to finish
resistance
R
ohms (Ω)
how much something resists letting current through, causes
electrical friction  causes heat
potential
difference
aka, voltage
electric power
ΔV
volts (V)
the ability (potential) to do work based on the difference
between charges
P
watts (W)
rate at which current is changed to potential difference (rate
means how much one things changes in relation to another
thing)
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?
CASTLE Assignment #1 - WHAT DO THE BULBS DO TO MOVING CHARGE?
AC/DC – not just a band!
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?
DC – direct current moves from one end to another. Batteries have fixed positive and negative ends. The +
end pushes current, the – end pulls. What happens when you switch the batteries around in a flashlight?
60 Hz – Hertz (Hz) measures frequency. 60 Hz means 60 reversals/second. American speed.
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:
Electrodynamics and Circuits
1
CASTLE Assignment #2 - INVESTIGATION TWO: COMPARING RESISTANCE
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
skin’s resistance from about 500,000Ω down to about 100Ω. How do lie detectors work?
GSR – Galvanic Skin Response – a measure of the skin’s conductivity
ΔV – potential difference (aka, voltage); measured in volts (V); how much pressure is pushing the current;
the energy source - 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 wide waterfall or a 9m wide
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?
Why are there so many kinds of 1.5V batteries? (AAA, AA, C, D)
P – electric power; measured in watts (W); the rate at which current, I, is changed to potential difference, ΔV.
Which uses more power, a 40W bulb or a 100W bulb?
Which one converts energy from an electrical form to a different form of energy the fastest?
What forms of energy does a light bulb convert electrical energy into?
Electrodynamics and Circuits
2
Electric companies sell energy, not power. Your electric bill is measured in kilowatts hour, kw x hr.
(Electrical Energy = Power x Time) 1kWhr = 3.6 x 106 Joules
New Equations! Yay!
Remember: m (milli) = 10-3, µ (micro) = 10-6, p (pico) = 10-12
E = Pt
Ohm’s and Watt’s Laws
Practice:
Use the equation in the
outer ring to find the
variable in the inner
circle.
Ex) V = IR (which is
Ohm’s Law, btw)
1. While working in the lab late one night, your eyes beheld an eerie sight. 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?
Electrodynamics and Circuits
3
3. How many electrons worth of charge 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 need to decrease the current in a wire but you only have more of that one type of wire to work with.
What do you do?
6. How much current is used by a toaster with 10.2 Ω resistance when plugged into a 120V socket?
7. An ammeter registers a current of 2.5A 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?
Electric Power & Energy – Ohm’s and Watt’s Laws and Energy equation HW
Electrodynamics and Circuits
4
Schematics - New pictures! Yay!
HW Circuits
Electrodynamics
and CircuitsAround
Draw the symbols; highlight why they look that way.
the World
5
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
Practice:
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 17a and 17b above.
Schematics: Types of Circuits – new equations! Yey!
Series
Parallel
Have to go through each resistor to get to
another. If one goes out, they all go out.
Can get to any resister w/o going through any other.
If one goes out, the others stay on.
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: V = V1 + V2 …
Potential difference parallel: V = V1 = V2 …
Remember: when you take the inverse of a variable, it goes under 1. Ex the inverse of R is 1/R.
Electrodynamics
and Circuits
CASTLE
Assignment
#3- WHAT MAKES CHARGE MOVE?
6
To solve for a series circuit
Step 1: Find the equivalent (total) resistance of
the circuit
RT  R1  R2
R =1 Ω
1
I
RT  1  1  2
Step 2: Find the total current supplied by the
battery
T
6V
R =1 Ω
2
Step 3: Find Voltage Drop across each resistor
Note: Since both resistors are the same, they
use the same voltage. Voltage adds in series
and voltage drops should add to the battery
voltage, 3V+3V=6V
To solve for a parallel circuit
Step 1: Find the total resistance of the circuit.
R1=1 Ω
1
1
1
1
RT
1
RT
R2=2 Ω
R3=3 Ω

R1

 11 
R2
1
2


R3
1
3
 116
so... RT  116  0.55
Step 2: Find the total current from the battery.
IT 
VT
RT

12V
0.55
 22 A
Step 3: Find the current through each resistor. Remember, voltage is the same on each
branch.
I1  VRT1  121V  12 A
12V
I 2  VRT2  122V  6 A
I 3  VRT3  123V  4 A
Step 4: Check currents to see if the answers follow the pattern for current.
I T  I1  I 2  I 3
I T  12 A  6 A  4 A  22 A
The
Electrodynamics and Circuits
total of the branches should be equal to the sum of the individual branches
7
Practice:
19. A 9.0V battery is connected to four light bulbs as shown below. Find the equivalent (total) resistance
and the total current for the circuit.
2.0 Ω4.0 Ω
5.0 Ω
7.0 Ω
9V
20. What is the voltage 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 current across each resistor?
HW Electric Circuits – Series and Parallel (on back of same page)
23.A house has a toaster, a microwave, and a coffee maker (all with built-in digital timers
that stay on) in parallel to each other and an overhead light in series with the other three
items all on a single 110V circuit. Draw a schematic diagram using of the circuit.
24.When will the appliances in parallel work right?
25.When will the light work at full power?
Electrodynamics and Circuits
8