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PHY301 Circuit Theory Assignment No 1 Solution Fall 2013

Q 1:   Find the equivalent resistance RTof 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.

Solution: 

Rt=4KΩ

It=5mA

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

Solution: V= 3.27KV

Q 3:      Answer the following questions.

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

Solution: 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.

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

Answer is 9 volt using formula from handouts.

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

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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