Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1...
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Transcript of Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1...
![Page 1: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/1.jpg)
Electricity
![Page 2: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/2.jpg)
The charge of an electron e=1.6×10-19 Coulomb
How many electrons are needed to make 1 Coulomb?6 x 1018
CAUTION
6,000,000,000,000,000,000 electrons
![Page 3: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/3.jpg)
Revision• Voltage is the energy gained or lost
by one Coulomb of charge.
• Current is the number of Coulombs flowing per sec.
• Resistance is the number of volts needed to push one Amp of current
EV
q
qI
t
VR
I
![Page 4: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/4.jpg)
![Page 5: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/5.jpg)
Series Circuit
• Adding resistors in series increases the resistance and decreases the current
2 A
6 V
1 A
6 V
![Page 6: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/6.jpg)
Parallel Circuit• Adding resistors in parallel
decreases the resistance and increases the current
2 A
6 V
2 A
6 V
2 A
4 A
![Page 7: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/7.jpg)
Internal Resistance
• If the wire’s resistance is 0.001 Ω, how much current flows?
![Page 8: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/8.jpg)
• The battery has got some resistance inside itself.
• We think of a battery like this:
![Page 9: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/9.jpg)
• The chemical reaction causes the charge to gain energy (or voltage increase).
• But it loses some energy (or voltage decrease) as it flows through because of the resistance.
![Page 10: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/10.jpg)
• The gain in voltage is called the EMF or electro motive force
![Page 11: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/11.jpg)
• The voltage loss in the internal resistance is:
• The output voltage of the cell is:
rV rI
Ir
rI
![Page 12: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/12.jpg)
Do Now: Ideal cell and real cell
Ideal cell: constant voltage output V without internal resistance (V=ε)Real cell: output voltage drops when the current increases due to internal resistance r.
![Page 13: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/13.jpg)
• When the current is zero, the output voltage is the EMF.
• So the EMF can be thought of as the output voltage when the current is zero
• i.e. if an AA cell is 1.5V, this is the EMF
oV Ir 0
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V
As the switches are closed, the current………
increases:
The voltage loss in the internal resistance ………..
increases
The output voltage goes ………
down
oV Ir
![Page 15: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/15.jpg)
Output Voltage
Current
oV Ir
EMF
Gradient =
r
![Page 16: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/16.jpg)
• Explain what happens to the lamp’s brightness if the rheostat slider moves to the right.
R I
Vo
Voltage across lamp
Power Brightness
oV Ir Ir
When the resistance of the rheostat increases, the total external resistance increases, and the current through the cell decreases. This leads to a smaller drop of voltage in the cell due to internal resistance. The voltage output of the cell increases, and there is more current going through the lamp. So the brightness of the lamp increases.
![Page 17: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/17.jpg)
Why do car headlights go dim when you start the engine?
![Page 18: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/18.jpg)
Why do car headlights go dim when you start the engine?
M12 V
0.1 Ω
![Page 19: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/19.jpg)
Why do car headlights go dim when you start the engine?
Turn on the light
M12 V
0.1 Ω12 A
0.9 Ω
1.2 V
10.8 V
![Page 20: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/20.jpg)
Why do car headlights go dim when you start the engine?
Turn on the starter motor
M12 V
0.1 Ω 60 A
0.9 Ω
6 V
6 V 0.1 Ω
![Page 21: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/21.jpg)
DC CircuitsCircuits can be very simple……
![Page 22: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/22.jpg)
Or complex …………
![Page 23: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/23.jpg)
• But we can simplify them with ………
Kirchhoff’s Rules
![Page 24: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/24.jpg)
Point RuleCurrent into a point equals current
out as the number of charges are conserved
I1
I2I1 + I2 =
I3
I3
![Page 25: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/25.jpg)
Loop RuleTotal voltage around a loop is zero as
the energy gained equals the energy lost.
Voltage gained
Voltage lost
0cell resistorV V
L H
HL
![Page 26: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/26.jpg)
• Example
Voltage gained
Voltage lost
2 1 0cell r rV V V
cellV
1RV 2RV
L H
HH LL
current
![Page 27: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/27.jpg)
• We could go the other way around
Voltage gained
Voltage lost
1 2 0r r cellV V V
L H
LL H H
![Page 28: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/28.jpg)
Cells are all 2.0 V, R1 = 3Ω, R2 = 1Ω
Find the current
First write a loop equation.
Solve: I = 0.5A
4 2 ( 1) ( 3) 0I I
I
![Page 29: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/29.jpg)
Do Now: find the current2A
I
5A
(a)
(b) (c)
![Page 30: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/30.jpg)
I
I
Voltage decrease
Voltage gain
Voltage gain
Voltage decrease
L H
L H
LH
LH
![Page 31: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/31.jpg)
Multi Loop Circuits
2V
2R
1R
1V
1I
2I
3I
2V 2 1I R 1 0V
Loop equation for top loop:
L H
HH
H
LL
L
![Page 32: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/32.jpg)
Bottom Loop
2V
2R
1R
1V
1I
2I
3I
1V 2 1I R 3 2 0I R
L H
L L HH
![Page 33: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/33.jpg)
Outer Loop
2V
2R
1R
1V
1I
2I
3I
2V 3 2 0I R
![Page 34: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/34.jpg)
Point Equation
2V
2R
1R
1V
1I
2I
3I
1I 2I 3I
![Page 35: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/35.jpg)
The circuit diagram shows a battery operated cappucino frother.
•Determine the battery voltage when the switch is open.
•Explain what happens to the the battery voltage when the switch is closed.
![Page 36: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/36.jpg)
• Battery voltage = 6.40 V• When the switch is closed, current
flows in the circuit.• This current flows through the
internal resistance.• This causes a voltage drop across
the internal resistance• The output voltage is less than the
EMF
V0 = ε - Ir
![Page 37: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/37.jpg)
When the switch is closed, the battery voltage is 6.25 V, and the current flowing is 0.450 A.
•Calculate the internal resistance.
•Calculate the motor’s resistance.V = ε – Ir6.25 =6.4 – 0.45r
9.13333.00.45
6.4R
6.4R)0.45(0.333
6.4 R)I(r :or
0IRIr6.4
rule loop Use
0.333Ω0.45
6.256.4r
![Page 38: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/38.jpg)
This shows two frother batteries being charged
![Page 39: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/39.jpg)
Calculate the current in the charger.
Calculate the value of R.
![Page 40: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/40.jpg)
Write a loop equation for the top loop.
![Page 41: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/41.jpg)
Ans.Use point rule: I = 0.250 + 0.208 =0.458AUse outer loop to find R:-6.4-0.25×1.5 -0.458R + 6.9 = 00.458R =6.9 - 6.4 -0.5×1.50.458R = 0.125R =0.273ΩFor top loop-6.4-0.25×1.5 +0.208×1.8 +6.4 = 0
![Page 42: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/42.jpg)
![Page 43: Electricity. The charge of an electron e=1.6×10 -19 Coulomb How many electrons are needed to make 1 Coulomb? 6 x 10 18 CAUTION 6,000,000,000,000,000,000.](https://reader036.fdocuments.in/reader036/viewer/2022081514/56649e5c5503460f94b53db0/html5/thumbnails/43.jpg)
I1
I3
I2
Ans.Point rule: I1= I2 + I3 (1)Outer loop:12 - 3I1- 5I3 = 0 (2)Bottom loop2 I2 + 4I2 - 5I3 = 0 or 6I2 - 5I3 = 0 (3)(3) => I2 =5I3/6 (4)(4) to (1)I1= 5I3/6 + I3 or6I1 = 11I3 or I1= 11I3/6 (5)(5) to (2)12 - 3× 11I3/6 – 5I3=012 - 11I3/2 – 5I3=0I3=24/21=8/7A (6)
(6) to (5):I1=11I3/6 =11×8/7/6 =88/42 =2.1AEffective resistanceR = 12/2.1=5.7ΩStandard equations:I1- I2 - I3=03I1+0I2 + 5I3 = 120I1+ 6I2 - 5I3 = 0