Experiment 1
Title: - Study the characteristics of LED, the relationship between LED voltage and
the wavelength of Light Emitted
Objective:
 Study the characteristics of LED
 Find the wavelength of Light Emitted
Apparatus:
 LED (Red, Green, Yellow)
 Power Supply (10V Variable)
 Resisters (1kΩ, 2.2kΩ,5kΩ,20kΩ)
Theory:
Like a common diode, the LED (Light Emitting Diode) consists of a P-N contact. When a PN
Junction is forward biased, current flows within it. This current flow will cause electrons and holes
to move is a manner that an electron will move to fill a hole. When this happens, the electron will
fall to a lower energy level and this will release an amount of energy in the form of photons. In a
larger scale, those photons will produce light.
LEDs are diodes and to light an LED, it must be forward connected. This means that the anode of
the LED must be connected to the positive pole of a battery, and the cathode must be connected to
the negative pole. This is how to determine the anode and the cathode lead of an LED. Determining
the anode and the cathode of a new LED is not very hard. The first way is from the length of its
leads. The anode lead is longer than the cathode lead of the led.
The energy radiated is proportional to the energy gap. The higher the energy gap, the greater the
frequency of emitted light.
Figure 1-1 Light Emitting Diode
Precautions:The following careful handling tips can definitely save you a lot of time and trouble while
operating with this useful equipment.
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The outer body of your breadboard is made up of plastic, so avoid exposing it to extreme
heat.
While bread boarding a circuit, the component distributions may not be that critical, but
their positioning will definitely require serious attention.
Avoid cramming the components and jumpers into particular compact areas; use the whole
breadboard space uniformly so that tweaking and troubleshooting the circuit becomes
easier.
If your circuit design is critical involving highly sensitive parameters, then using a
breadboard assembly probably won’t be a good idea, because the close proximity of their
tracks and the jumpers may induce stray capacitance producing spurious results.
Do not apply mains voltages directly to the breadboard circuitry because again the closely
situated connections may possibly create arcing or even dangerous short circuits and a fire.
Band Gap
𝐸𝑔 = ℎ𝑓
Since
𝐸𝑔 = ℎ𝑐/λ
λ = Wavelength
c = velocity of light = 3x108 m/s
h = Plank’s Constant = 6.636x10-34 J.sec
Vknee = Vth = Eg = VLED
λ = wavelength = 1.24 / Eg
Circuit Diagram:
Observation (in Forward Bias)
VCC
R(Ω)
VR
VLED =EG
LEDCOLOUR
OBSERVATION
VCC
R(Ω)
VR
VLED=EG
LEDCOLOUR
OBSERVATION
VCC
R(Ω)
VR
VLED=EG
LEDCOLOUR
OBSERVATION
Graphs
Conclusion
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Rubrics
Psychomotor Domain
Criteria
Poor
Average
Good
Very Good
Excellent
1
2
3
4
5
More than 15 minutes late
More than 10 minutes but less than
15 minutes late
More than 5 but less than 10
minutes late
Less than 5 minutes late
Right on time
Demonstrate either no,
incomplete or incorrect
operational skills and is unable to
identity parameters and
uncertainties
Has basic idea but in need of
extreme supervision and steering in
right direction
Establishes above average
apparatus operational skills to
utilize the apparatus effectively,
with no amount of damages to the
apparatus
Establishes good apparatus
operational skills to utilize the
apparatus effectively, with no
amount of damages to the
apparatus
Establishes excellent
apparatus operational skills
to utilize the apparatus
effectively, with no amount
of damages to the
apparatus
Software Usage
Demonstrate either no,
incomplete or incorrect
operational skills and is unable to
identity parameters and
uncertainties
Has basic idea but in need of
extreme supervision and steering in
right direction
Establishes above average
connections, operational skills to
utilize the software effectively but
requires supervision
Establishes good connections,
operational skills to utilize the
software effectively with
minimum supervision
Establishes excellent
connections, operational
skills to utilize the software
effectively with no no
supervision
Timely Completion
Could not perform the experiment
at all
Partially completed with little
meaning-fullness
Completed with little extra time
Completed the task within the
specified period
Completed the task before
specified period
Data Acquisition
Data is incorrect or missing
entirely. Relevant units or labels
are missing
Data is incomplete or does not
include sufficient details. Relevant
units or labels are incorrect
Data is complete but does not
comprehensive details. Relevant
units or labels are partially correct
Data is complete and correct.
Sufficient details are provided
Data is complete and
correct. Student provided
details.
Data Analysis and
Interpretation
Did not analyze any data
Analyzed some data but did not
answer any questions
Analyzed some data and
answered some questions
Analyzed most of the data and
answered most of the
questions
Analyzed all of the data and
answered all the questions
Punctuality
Equipment Usage
Score
Psychomotor Total
Affective Domain
Criteria
Poor
Average
Good
Very Good
Excellent
1
2
3
4
5
Responsiveness to
queries / questions
Could not comprehend
questions at all
the
Needed extra tips to comprehend the
questions
Took more than average time to
comprehend the questions
Took average or less than
average time to comprehend
the questions
Immediately comprehended
the questions
Lab Work (manual)
presentation
No or very little write up. Missing
almost all the parts in the manual.
Directed to rewrite
Write up of all the parts but with major
mistakes. Directed to correct the
mistakes
Write up of all the parts but with
minor mistakes. Directed to correct
the mistakes
Write up of all the parts with no
mistakes. Few cleanliness
issues in write up. No
corrections required
Write up of all the parts with
no mistakes. No cleanliness
issues in write up. No
corrections required
Affective Total
Signature_______________
Score