lecture in electrical power
TRANSCRIPT
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Lecture 6: Electrical Power
1. Electrical energy & power
2. Electrical activity in the heart
3. Examples and Quizzes
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Electrical Energy and Power In a circuit, as a charge moves through the
battery, the electrical potential energy of thesystem is increased by QV The chemical potential energy of the battery
decreases by the same amount
As the charge moves through a resistor, it losesthis potential energy during collisions with atomsin the resistor
The temperature of the resistor will increase
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Three resistors are connected in series in a circuit. Theresistors A, B, and C have resistances R, 2R, and 3R,
respectively. Which resistance dissipates the mostpower?
1 2 3 4
25% 25%25%25%
1. A2. B
3. C
4. They all dissipatethe same power
when in series.0
0
5
30
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A circuit element uses 50 watts of power. The currentrunning through it is 5 A. Which of the following could
be the circuit's resistance and potential difference?
1 2 3 4
25% 25%25%25%1. 2.
3. 4.
0
0
5
30
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Energy Transfer in the Circuit Consider the circuit
shown Imagine a quantity of
positive charge, Q,
moving around thecircuit from point Aback to point A
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Energy Transfer in the Circuit,cont
Point A is the reference point
It is grounded and its potential is taken to bezero
As the charge moves through the battery
from A to B, the potential energy of thesystem increases by QV The chemical energy of the battery decreases
by the same amount
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Energy Transfer in the Circuit,final
As the charge moves through the resistor, from
C to D, it loses energy in collisions with theatoms of the resistor
The energy is transferred to heat
When the charge returns to A, the net result isthat some chemical energy of the battery hasbeen delivered to the resistor and caused itstemperature to rise
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Electrical Energy and Power,cont
The rate at which the energy is lost is the
power
From Ohms Law, alternate forms of powerare
QV I V
t
= =
2
2 VI R
R
= =
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Electrical Energy and Power,final
The SI unit of power is Watt (W)
I must be in Amperes, R in ohms and V inVolts
The unit of energy used by electric
companies is the kilowatt-hour This is defined in terms of the unit of power
and the amount of time it is supplied
1 kWh = 3.60 x 106 J
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Electrical Activity in the Heart Every action involving the bodys muscles
is initiated by electrical activity Voltage pulses cause the heart to beat
These voltage pulses are large enough tobe detected by equipment attached to theskin
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Operation of the Heart
The sinoatrial (SA) node initiatesthe heartbeat
The electrical impulses cause theright and left artial muscles tocontract
When the impulse reaches theatrioventricular (AV) node, themuscles of the atria begin to relax
The ventricles relax and the cyclerepeats
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Electrocardiogram (EKG)
A normal EKG P occurs just before the
atria begin to contract
The QRS pulse occurs
in the ventricles justbefore they contract
The T pulse occurswhen the cells in the
ventricles begin torecover
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Abnormal EKG, 1
The QRS portion iswider than normal
This indicates the
possibility of anenlarged heart
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Abnormal EKG, 2
There is no constant relationship between P and QRS
pulse This suggests a blockage in the electrical conductionpath between the SA and the AV nodes
This leads to inefficient heart pumping
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Abnormal EKG, 3
No P pulse and an irregular spacing between the QRSpulses
Symptomatic of irregular atrial contraction, calledfibrillation
The atrial and ventricular contraction are irregular
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Implanted CardioverterDefibrillator (ICD)
Devices that canmonitor, record andlogically process heartsignals
Then supply differentcorrective signals tohearts that are not
beating correctly