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# Assignment 1(Fall 2013)

Circuit Theory (Phy301)

Marks: 25

Due Date: November 18, 2013

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Q 1:

Find the equivalent resistance RT of given circuit and current flowing through equivalent circuit. Write each step of the calculation to get maximum marks. Draw the circuit diagram of each step otherwise you will loose marks.

Q 2:

Determine the voltage and current across 2kΩ resistor for the given circuit. Mention the units of calculated value. Q 3:

1.              I.      Write the differences between alternating current (AC) and direct current (DC).

1.           II.       A 12V battery is connected across two series resistances of value 2kΩ and 6kΩ. Determine the voltage drop across 6kΩ resistor.

1.        III.      What does the term “Conventional current” and “Electron current” mean?

……………………………………………

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Write the differences between alternating current (AC) and direct current (DC)

DIRECT, CONTINUOS OR GALVANIC CURRENT:
Appears with the abbreviations DC (direct current in English).
It is the current that flows just in one direction: from the positive to the negative pole, if we consider the conventional sense of the current, or from the negative pole to the positive pole considering the direction of current flow of electrons. Direct current can be found in devices that having two poles: one negative and one positive. Cells and car batteries are the best examples where we can find this type of current.

ALTERNATING or ALTERNATE CURRENT
Appears with the abbreviations CA or AC (Alternating Current from English).
As the name suggests, is the type of power that constantly switches direction. In alternating current poles dont exists, but phases, because the electrons vary continuously of polarity. These variations take place at a given frequency, in the case of European countries is 50 times a second (50 Hertz) and in the U.S. is 60 times a second (60 Hz). We find alternating current in our houses, in power stations, alternators in cars, etc.

Write the differences between alternating current (AC) and direct current (DC)

The difference between alternating current (AC) and direct current (DC) is that in direct current (DC), the electrons travel in one direction while in alternating current (AC), the electrons travel in alternate directions. Alternating current (AC) is used to transport electricity over long distances due to minimal loss. Direct current (DC) was discovered before alternating current.

Electron Current vs. Conventional Current
In 1752, prior to electricity being identiﬁed with the electron, Ben Franklin chose a convention
regarding the direction of current ﬂow. Franklin assumed that electrons (being assumed positive)
ﬂow from positive to negative terminals. We now know this is incorrect. The charge on an electron
is negative by deﬁnition (note negative sign): (-1.6x10-19 C)
The ﬂow of electrons is termed electron current. Electrons ﬂow from the negative terminal to the
positive.Conventional current or simply current, behaves as if positive charge carriers cause current
ﬂow. Conventional current ﬂows from the positive terminal to the negative.
Perhaps the clearest way to think about this is to pretend as if movement of positive charge carriers
constituted current ﬂow.
It is important to realize that the difference between conventional current ﬂow and electron ﬂow in
no way effects any real-world behavior or computational results. In general, analyzing an electrical
circuit yields results that are independent of the assumed direction of current ﬂow. Conventional
current ﬂow is the standard that most all of the world follows.
electron ﬂow
electron ﬂow
current ﬂow
current ﬂow
Conventional current ﬂow is opposite to electron ﬂow
+
-
1.5V
zap-o-matic

For equivalent Resistance

R(eq)= R1+R2+R3.............Rn

For Voltage

V=IR

R=11

I=2

V=22

Please correct me if i'm wrong

# Write the differences between alternating current (AC) and direct current (DC).

There are no doubt many differences that could be mentioned, but I think the most important ones are adequately covered below:

Alternating current periodically changes the polarity of voltage and consequently the direction of flow also periodically changes. A full set of changes from zero (volts or amps) through all of the positive values, zero, then all the negative values and back to zero again is called "one cycle". The number of cycles occurring every second is called its "frequency" and the unit of measurement is "Hertz" (Hz) with one cycle per second being equivalent to one Hertz. AC power is commonly supplied at a substantially constant value of 50Hz or 60Hz dependent upon the National specification. AC power is most commonly generated by an electro-mechanical machine usually called an "alternator", which is usually designed to deliver either a "single phase" or a "three phase" output with approximately "sinusoidal" waveform.

Direct current is delivered from a supply whose polarity of output voltage is constant, thus it causes current to flow in a single direction. The value of the dc output voltage is substantially constant, and in such circumstances, it is meaningless to talk about its "frequency", though it is sometimes said to be zero Hertz. Note that if a dc supply is periodically "interrupted" (turned on and off or "chopped") it will become a unipolar square wave and effectively acquire "a.c. components" whose frequencies can be specified.
DC supplies are commonly obtained from electrochemical "cells" or "batteries"; photoelectric cells; and thermocouples; as well as electromechanical devices sometimes called "dynamos".

Current flow in a pure dc circuit is determined by the value of the voltage, and the resistance(s) of the component(s) in the circuit, according to "Ohm's Law" which may be expressed by the formula
I = V/R
where I is the current in Amps; V is the voltage in Volts and R is the resistance in Ohms.

In an ac circuit the current is determined by the voltage (which is usually expressed as an r.m.s. value or less often as an "amplitude" a.k.a. "peak value") and the so called "impedance" (Z) where Z is determined by both Resistance (which is largely independent of frequency) and the frequency dependant "Reactance" (X) , the latter having two forms referred to as "Capacitive Reactance" and "Inductive Reactance".

Reactance has no real meaning in a pure d.c. circuit, but is of fundamental importance in a.c. circuits.

Difference between DC and Ac?

In Direct Current (DC), the current flows IN THE SAME DIRECTION. That is, if you have a wire through which DC is flowing, then one end will be permanently positive terminal, and the other, the negative terminal.

In Alternating Current (AC), the current CHANGES ITS DIRECTION OF FLOW periodically. That is, the same end once becomes the positive terminal for one cycle, and then becomes the negative terminal in the 2nd cycle. So the current once flows in forward direction, and again in reverse direction.
The number of changes of direction in one second is called the frequency of the AC.
Most of the time it is 50 Hz. That means, the current changes its direction for 50 times in one second.

DC current comes from dry cells, batteries etc.
AC comes from most of the power supply stations

Q no 3

2parts  my ans is 9 volts ..by using the formula in Handouts

Qno3  part 3

What does the term Conventional current and Electrical current means ?

Electric current is the rate of charge flow past a given point in an electric circuit, measured in Coulombs/second which is named Amperes. In most DC electric circuits, it can be assumed that the resistance to current flow is a constant so that the current in the circuit is related to voltage and resistance by Ohm's law. The standard abbreviations for the units are 1 A = 1C/s.

The ﬂow of electrons is termed electron current. Electrons ﬂow from the negative terminal to the
positive.Conventional current or simply current, behaves as if positive charge carriers cause current
ﬂow. Conventional current ﬂows from the positive terminal to the negative.
Perhaps the clearest way to think about this is to pretend as if movement of positive charge carriers
constituted current ﬂow.

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A 12V battery is connected across two series resistances of value 2kΩ and 6kΩ. Determine the voltage drop across 6kΩ resistor.

first find the total resistance 2k + 6K = 8K

so the current through them is I = V / R = 12 / 8000 = 0.0015 amps

so across the 6k resistor with 0.0015 amps flowing through it, is V = I x R = 6000 x 0.0015 = 9 volts

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