Solved problems

Solved Problems

Q 1) Calculate the equivalent resistance across AB. Find the current draw from the battery. You may refer  figure 5.1.

  a)      Then find the voltage across 9 Ohms resistance.

  b)      Find the voltage between AD.

  c)       Find the current through 18 Ohms resistance.

Answer :

Resistance across AC = (6/2) = 3 Ohms-----------( as the resistance are equal, R = r/n )

Resistance across AD = (3+6) // 18 = {9*18/ (9+18)}  = 6 Ohms

Resistance across AB = 6+9 = 15 Ohms

Now we can find the current drag from the battery by using this equivalent resistance across AB.

Ohm’s law to R_ab,

V = IR

60V = I X 15

I = 4A

    a)      As there are no parallel paths between AB , current through 9 Ohms resistance is equal to 4A .  Ohm’s law  to 9 Ohms resistor,
V = IR

Vdb = 4A x 9 Ohms
Vdb = 36V

     

     b)      Since,
V ab = V ad + V db

V ad = Vab – V db

V ad = 60 – 36

V ad = 24 V

     c)       Current through 18 Ohms  can be calculate by Ohm’s law
Vad = I x 18
     I = (24/18) A
     I = (4/3) A

Q2)  Find the equivalent resistance across AB in every circuit.

i)                    Each resistance is 3 Ohms

Figure 5.2

Answer :

                  

Figure 5.2.1

Figure 5.2.1 shows the way to calculate the equivalent resistant

Rab  =  3 + 1.5 + 1 + 3 =  8.5 Ohms

ii)                   

Answer :

Then we can simplify this circuit as shown in figure 5.3.2

After therse steps the problem becomes a very simple one.

Rab = 0.5 Ohms

Exercise

Q3)  

i)                    Find the current draw from the circuit in figure 5.2 (Q2. i )  if  60 V voltage is given to AB .

ii)                  Find the voltage difference between every  resistance

iii)                Then find the current through every resistance

Q4)i)                    Find the current draw from the circuit in figure 5.3 (Q2. ii )  if  60 V voltage is given to AB .

ii)                  Find the voltage difference between every  resistance

iii)                Then find the current through every resistance

Q5)   i) Find the total current draw from the battery in Figure 6.1     Ans (3A)

         ii) Calculate the power supplied by battery in figure 6.2           Ans(72W)

         iii) Find the total resistance seen by the battery in figure 6.3 . find the current draw from it. 

         Ans (1.5 Ohms , 8A  )

NOTE : In figure 6.1 The resistance are parallel connected (12 Ohms & 6 Ohms ) .

              In figure 6.2 Again you may see that all three resistors are parallel connected.

               In figure 6.3 Again you may see that all four resistors are parallel connected.

to understand these things you need to solve more problems and gain experience.

               

Pabindu lakshitha

B.sc (Engineering undergraduate)