Electronics - Series Circuits - Discussion

Consider a pratical condition in your life.

When you entering into a Cinema hall which way you prefer first?

1)Exit in which all crowd are coming out in opposite to you.
2)Entrance no crowd is coming opposite to you.

obivously 2nd one ryt.

Same here in the case of current it goes in the way which offers very less resistance.

Ammeter's internal resistance is very low so it acts as bypass circuit

path for current so R1 will be short circuited.

If insted of Ammeter there is Rheostat set for a high value more current will be flowing through R1.

V=120volts
I=0.116Amps

RT=R1+R2+RL+R3

RT=V/I (Since all circuit elements are in series)

RT=120/0.116 =1034.482ohms

2000+500+500+RL = 1034.482

RL= 1034.482 - 3000 (Resistance cannot be negative in linear circuit)

Here R1 is the value greater than RT by making RT short

RL=1034.482 -1000

RL = 34.482ohms

VRL = 34.482x.116 = 4V

You can see 4V across Lamp in circut given

So the circuit is correct when R1 2k is short circuited.

Wrong in the circuit for given condition is there is no R1 in circuit or R1 is short circuited.

Answer is B --> R1 is Shorted

Explanation : - Drop across R1 is v = 0.116*2000 = 232 Volts (In order to this be true the input voltage must be more than 232 Volts )

As the input is just 120 Volts in this case, the above drop is not possible. Hence R1 needs to be removed.

If we replace it with OPEN circuit then circuit will not function so R1 is replaced with a short circuit.

By KVL-

=> 120V - .116(R1+R2+R3)- 3.721V = 0
=> 120V - .116(0+500+500)- 3.721V = 0 (Say R1 = Short(0))
=> 120V - 116 - 3.721 = 0
=> 120V - 119.721V = 0
=> .179 = 0 is aprox 0 = 0

So the Ans. B is correct

If there's no R1 and it is shorted, then the values are all correct.

Because the Voltage of R1 is exceed 120V, which is not possible of other values.
VR1= 0.116*2000= 232V, that's wrong.

When the resistors are in a series manner so it doesn't open it, if the resistor R1 is opened the circuit doesn't work, So the Answer is "The resistor R1 is Shorted".

Simply apply KVL rule for circuit. Here 500 ohm is placed negative voltage side. So r1 is wrong for that place.

What if R2 is open? There is no circuit and no ammeter and voltmeter readings if R2 is open.

v = 120,
r = 2k.
i = v/r so,120/2000=0.06,
R1 = shorted.

See the figure correctly and you can identify easily.