# VU HELP

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# Assignment 1(Fall 2015)

Circuit Theory (PHY301)

Marks: 30

Due Date: November 12, 2015

DON’T miss these important instructions:

• To solve this assignment, you should have good command over first 6 lectures.
• Upload assignments properly through LMS, (No Assignment will be accepted through email).
• All students are directed to use the font and style of text as is used in this document.
• Don’t use colorful back grounds in your solution files.
• Use Math Type or Equation Editor etc for mathematical symbols.
• This is not a group assignment, it is an individual assignment so be careful and avoid copying others’ work. If some assignment is found to be copy of some other, both will be awarded zero marks. It also suggests you to keep your assignment safe from others. No excuse will be accepted by anyone if found to be copying or letting others copy.
• You can draw circuit diagrams in “Paint” in “Corel Draw” or in circuit maker. The simple and easy way is to copy the given image in Paint and do the required changes in it.

Q 1:

Find the equivalent resistance RT of given circuit. Write each step of the calculation to get maximum marks. Draw the circuit diagram of each step otherwise you will lose marks.

The total resistance of circuit is=

4+2 of two series resistances = 6 ohm for above mentioned circuit.

Then total of above circuit = 6*6/6+6= 3 ohm

The total resistance for this part is= 4*4*4/4+4+4= 1.34 ohm

Resistance of this part is 1+1.34+5 = 7.34

Resistance of this part is 3+1+3= 7

Resistance of this part is 7*7.34/7+7.34= 3.58

Thus after redesigning whole circuit it will be

The total resistance of whole circuit is= 5+3.58+1= 9.58 ohms

Q 2:

Find the current through each resistor and power dissipation across 20kΩ Resistance. Write each step of the calculation to get maximum marks and also mention the units of each derived value.

(a)    Is it right to say that every short circuit is a close circuit while every close circuit is not short circuit. Justify your answer

Answer: The circuit where both terminals are connected in a loop is called a close circuit. The circuit having a load/resistance also a close circuit but due to resistance we can’t transmit maximum amount of current from one terminal to other. On the other hand where both terminals connected in loop but resistance between both terminals is approximately zero then we can say this is a short circuit.

As we saw the loop with a load also is a close circuit and short circuit is also closed by keeping this in mind we can say every short circuit is closed and every closed circuit is not a short circuit because the close circuit may have a load b/w both terminals.

(b)   What is the use of circuit breaker and Fuse in electric panel/wiring?

Answer: We use circuit breakers and fuses in electric panel/wiring to save appliances from over amount of current to pass from them. As every electrical equipment bear a certain amount of current in case when over current moves in the circuit of equipment it may damage the equipment. To avoid such condition we use fuses and breakers the fuse melt down when over current try to pass from it by this the circuit break down and turn the supply off to save electric appliances. The same purpose of breaker it switch off when current or exceed a certain value.

(c)    Write the names of different instruments/devices used to measure the voltage and current across a circuit element & way to connect them.

Volt Meter: We use volt meter to measure amount of voltages in a circuit. We connect volt meter in parallel to measures voltages as the voltages remain same in a parallel circuit.

Ampere meter:

Ampere meter is used to measure the amount of current in circuit as we know that current remain same in series so we connect ampere meter in series to check amount of current in a circuit.

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