Two coils each of 250 ohm. Resistance are connected in series across a...
Problem Statement
Two coils, each of 250 ohm resistance, are connected in series across a constant voltage. Calculate the value of resistance to be connected in parallel with one of the coils to reduce the potential difference across its terminal by 1%?
Solution
Let's start with some basic concepts of series and parallel resistors.
Series Resistors
When resistors are connected in series, the total resistance of the circuit is the sum of the individual resistances:
RS = R1 + R2 + R3 + ... + Rn
Parallel Resistors
When resistors are connected in parallel, the total resistance of the circuit is given by:
1/RP = 1/R1 + 1/R2 + 1/R3 + ... + 1/Rn
RP = (R1 * R2 * R3 * ... * Rn) / (R1 + R2 + R3 + ... + Rn)
Calculating the Total Resistance
In this problem, we have two coils each of 250 ohm resistance connected in series. Therefore, the total resistance of the circuit is:
RT = R1 + R2 = 250 + 250 = 500 ohm
Reducing the Potential Difference
To reduce the potential difference across one of the coils by 1%, we need to connect a resistor in parallel with it. Let's call this resistor RX.
The potential difference across the coil is given by:
V1 = I * R1
where I is the current flowing through the circuit.
If we want to reduce the potential difference across the coil by 1%, we need to have:
V1 - 0.01 * V1 = 0.99 * V1
Therefore, we need to have:
I * R1 = 0.99 * (I * R1 + I * RX)
After simplification, we get:
RX = R1 * (0.99 - 1) / 1 = -2.5 ohm
This means that