---
title: 'Switched RL Series Circuit: Time Constant'
topic: Circuits
author: Joseph Wandinger
source: 2.14.57
template_version: 1.3
attribution: openstax-physics-vol2
partialCredit: true
singleVariant: false
showCorrectAnswer: false
outcomes:
- 21.14.3.0
- 21.14.3.1
difficulty:
- undefined
randomization:
- undefined
taxonomy:
- undefined
span:
- undefined
length:
- undefined
tags:
- OSUP
- volume 2
- chapter 14
- problem 57
- circuits
- inductance
- RL circuits
- multi-part
- JW
assets:
- fig_OSUPv2p14_57.png
part1:
type: number-input
pl-customizations:
label: $\tau_L = $
allow-blank: false
show-correct-answer: false
comparison: relabs
rtol: 0.03
atol: 0
show-help-text: true
suffix: $\rm\ s$
weight: 1
custom-format: .3g
part2:
type: number-input
pl-customizations:
label: $R = $
allow-blank: false
show-correct-answer: false
comparison: relabs
rtol: 0.03
atol: 0
show-help-text: true
suffix: $\rm\ \Omega$
weight: 1
custom-format: .3g
myst:
substitutions:
params_vars_title: 'Switched RL Series Circuit: Time Constant'
params_t: '1.95'
params_L: '270.0'
---
# {{ params_vars_title }}
Consider the $RL$ circuit shown below.
The current in the circuit reaches half of its maximum value in ${{ params_t }}\rm\ ms$ after switch $\rm S$ is thrown.
## Part 1
Determine the time constant $\tau_L$ of the circuit.
### Answer Section
Please enter in a numeric value in $\rm\ s$.
## Part 2
Given $L = {{ params_L }}\rm\ mH$, determine the resistance $R$ of the circuit.
### Answer Section
Please enter in a numeric value in $\rm\ \Omega$.
### pl-submission-panel
{{ feedback.part1_ans }}
{{ feedback.part2_ans }}
### pl-answer-panel
$\tau_L =$ {{ correct_answers.part1_ans_str }} $\rm\ s$
$R =$ {{ correct_answers.part2_ans_str }} $\rm\ \Omega$
## Attribution
Problem is from the [OpenStax University Physics Volume 2](https://openstax.org/details/books/university-physics-volume-2) textbook, licensed under the [CC-BY 4.0 license](https://creativecommons.org/licenses/by/4.0/).
![Image representing the Creative Commons 4.0 BY license.](https://raw.githubusercontent.com/firasm/bits/master/by.png)