lecture in electrical power

7/30/2019 Lecture in electrical power

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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

lecture in electrical power

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