What is the forward voltage of LED?

This question was previously asked in
RRB ALP CBT 2 Electronic Mechanic Previous Paper: Held on 23 Jan 2019 Shift 1
View all RRB ALP Papers >
  1. 0.6 Vdc
  2. 1.5 Vdc to 3 Vdc
  3. 0.3 Vdc
  4. 1.8 Vdc to 3.3 Vdc

Answer (Detailed Solution Below)

Option 4 : 1.8 Vdc to 3.3 Vdc
Free
General Science for All Railway Exams Mock Test
2.1 Lakh Users
20 Questions 20 Marks 15 Mins

Detailed Solution

Download Solution PDF
  • light-emitting diode (LED) is a semiconductor light source that emits light when current flows through it.
  • The forward voltage of an LED, VF, is the voltage that must be applied across the leads of the LED, from anode to cathode, in order for the LED to turn on.
  • Typically, the forward voltage of an LED is between 1.8 and 3.3 volts.
  • It varies by the color of the LED.
  • A red LED typically drops around 1.7 to 2.0 volts.
  • Since both voltage drop and light frequency increase with band-gap. 
  • A blue LED drops around 3 to 3.3 volts.

F2 Neha Madhu 29.10.20 D3

Latest RRB ALP Updates

Last updated on Jun 26, 2025

-> RRB ALP Exam Date OUT. Railway Recruitment Board has scheduled the RRB ALP Computer-based exam for 15th July 2025. Candidates can check out the Exam schedule PDF in the article. 

-> Railway Recruitment Board activated the RRB ALP application form 2025 correction link, candidates can make the correction in the application form till 31st May 2025. 

-> The Railway Recruitment Board (RRB) has released the official RRB ALP Notification 2025 to fill 9,970 Assistant Loco Pilot posts.

-> The Railway Recruitment Board (RRB) has released the official RRB ALP Notification 2025 to fill 9,970 Assistant Loco Pilot posts.

-> The official RRB ALP Recruitment 2025 provides an overview of the vacancy, exam date, selection process, eligibility criteria and many more.

->The candidates must have passed 10th with ITI or Diploma to be eligible for this post. 

->The RRB Assistant Loco Pilot selection process comprises CBT I, CBT II, Computer Based Aptitude Test (CBAT), Document Verification, and Medical Examination.

-> This year, lakhs of aspiring candidates will take part in the recruitment process for this opportunity in Indian Railways. 

-> Serious aspirants should prepare for the exam with RRB ALP Previous Year Papers.

-> Attempt RRB ALP GK & Reasoning Free Mock Tests and RRB ALP Current Affairs Free Mock Tests here

More Optical Sources and Detector Questions

Get Free Access Now
Hot Links: teen patti royal teen patti gold download teen patti lucky lucky teen patti