SECTION B:ACTIVITIES

ACTI VITY B1
AIM
To identify a diode, an LED, a resistor and a capacitor from a mixed collection of such
items.

APPARATUS AND MATERIAL REQUIRED

A multimeter, a mixed collection of diode, LED, resistor and capacitor.

THEORY

Diode. A two terminal device which conducts current when forward biased and not when reverse
biased. It does not emit light during its conduction.
LED. A light emitting diode is a two terminal device which conducts current when forward biased and
not when reverse biased. It emits a characteristic light during its conduction.
Resistor. A two terminal device which conducts equally in both directions.
Capacitor. A two terminal device which offers infinite resistance to dec but has a finite reactance for ac.
When connected across a dc source, a multimeter shows a large current initially (for C >uF) which
decreases to zero quickly. This is because the capacitor initially draws a charge.

DIAGRAMS
Violet -
Orange
Red- Silver

Carbon resistor Diodes

1000 u LED
6 V
(0.47 F
P'aper
Electrolytic
Mica
CAPACITORS

Fig. 1 Diagrams of carbon resistor, diodes, LED and capacitors.

PROCEDURE
.Look for the colour bands on the given components. If a component has a set of three colour bands
followed by a silver or gold band, then the component is a resistor.
2. Insert the black and red leads (or probes) into common and positive terminals of the multimeter.
Turn its selector switch to resistance mode- highest range (0-MD).
. Touch the two probes to the two ends of each component one by one. Note the direction of
deflection in the multimeter. Interchange the positions of two probes tor each component and again
note the direction of deflection.
4. If the multimeter shows an equal deflection in both directions, then the component is a resistor.

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5. If a multimeter shows deflection in one direction without any emission light

and no deflection in the opposite direction, then the component is a diode,
of from the
the ccomponen
.lf the multimeter shows deflection in one direction alongwith the emission of light
component and no deflection in the opposite direction, then the component is an LED from the
t the multimeter does not show any deflection on connecting its probes either way to a comn.
then the component is a capacitor, But if the capacitance of the capacitor is large, the m
will show a large deflection initially which gradually decreases to zero.
8. Kecord all your observations in a tabular form.

OBSERVATIONS
Table B1 State of conduction of each component

Item code State of conduction of a component Identified component

A
Conducts equally in both directions
B Conducts in one direction without emission of light
C Conducts in one direction with emission of light
D Does not conduct, gives an initial deflection which
decays to zero

RESULT
From the mixed
grouping of components, the components marked A, B, Cand Dhave been identified
resistor, diode, LED and capacitor respectively.
as

PRECAUTIONS
1. While
checking the conduction state of any component, clean its leads properly.
2. Use the selector switch of the
multimeter in resistance mode with
3. While testing
highest range option.
any component, avoid touching the metal end of either of
multimeter probe. Body
resistance in parallel with the component resistance
may create confusion about the conduction
state of the component.

VVA VOCE
1. What is a resistor ?
5. How do the conduction states of
Any material that has some resistance is called a and an LED differ?
an ordinary diode

resistor.
An
2. What is a linear resistor ?
ordinary diode conducts in torward biasing
without any emission of light while an LED conducts
A linear resistor is one which obeys Ohm's law in forward direction with
or for emission of light. Both do
which V-I graph is a straight line passing not conduct in reverse
through the biasing.
origin. 6. How does a
capacitor behave towards dc?
3. What is a non-ohmic device ? A capacitor does not conduct dc. But a capacitor or

A device which does not obey Ohm's law is called a large capacitance shows an initial deflection in the
non-ohmic device. Semiconductor diodes, LEDs, etc; ammeter which decays to zero quickly. This is due to
are non-ohmic devices. charging of the capacitor.
4. Does an ohmic resistor conduct equally for both 7. How does capacitor behave towards ac?
a

forward and reverse biasing? A

capacitor conducts ac because its capacithve
Yes, an ohmic resistor conducts equally when current is
passed in one direction and then in opposite direction. reactance|X% is finite against ac.
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