Question

A coil of 10 H inductance and 5Ω resistance is connected in parallel with a 20 Ωresistor across a

100-V d.c. supply which is suddenly disconnected. Find (i) the initial current after switching (ii)

the voltage across the 20 Ωresistor after 0.3 sec.​

Answer 1

Answer:

find the area of a triangle with base 44 cm and whose height is equal to the of breadth rectangle with length 18 cm and area 126cm square. the area of the

red triangle in terms

of X, if the black

quadrilateral is a

rectangle.

2x

2x

12 cm

9cmfind the area of a triangle with base 44 cm and whose height is equal to the of breadth rectangle with length 18 cm and area 126cm square.

Answer 2

Concept:

We need to utilize the ohms law as, V = IR and another equation represented as, t = L/R

Given:

The inductance of  Coil = 10H

Resistance of coil = 5ohm

Resistor = 20ohm

D.C. supply = 100 V

Find:

We need to determine the initial current after switching and the voltage across the 20ohm resistor after 0.3seconds.

Solution:

At t > t < 0

100 V will be turned on inductor will be shorted circuit.

Req = 20ohm ║ 5 ohm = 20 × 5/ 25

R = 100/25 = 4ohm

Initial current, i(0⁻) = V/R = 100/4 = 25A

At t > 0 i(0⁻) = i(0) = i(0⁺) = 25A

Req = 20 + 5 = 25 ohm

Time = L/R where L is the inductance and R is the resistance

0.3 = 10/25

i(t) = i(0)e⁻t/0.3

= 25e⁻t/0.3

= 25.e⁻3.3t A

Voltage, v(t) = i(t)R

v(t) = 25.e⁻3.3t × 20 V

Thus, the initial current after switching is 25A and the voltage across the 20 Ω resistor after 0.3 sec is 25.e⁻3.3t × 20 V.

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