THINGS TO BE WRITTEN ON RIGHT HAND SIDE
ACTIVITY I
AIM
To measure resistance, voltage (AC/DC), current (AC) and check continuity of a
given circuit using multimeter.
APPARATUS AND MATERIAL
Three carbon resistors, one standard resistance coil, a battery eliminator with
tapping (2 V, 4 V and 6 V), a step-down transformer (6- 0-6 V) with two tapping
(2 V and 4 V), a resistor of 100 ohm, a plug key and multimeter.
THEORY
Multimeter.
It is a single measuring device acting as an Ammeter, a Voltmeter and an
Ohmmeter. For this reason, it is also called AVO meter.
It can measure alternating as well as direct current and alternating as well as
direct voltage in addition to resistance. For this purpose its panel is divided
into five different sections. There are many ranges in each section so that it
can measure from micro (10-6) to mega (106) units.
Carbon resistors:
1. Carbon resistors are frequently used in electrical and electronic circuits
and their values vary over a very wide range. A colour code is used to
indicate the value of the resistance.
2. A carbon resistance has four different concentric coloured bands on its
surface. The first three bands a, b and c determine the value of the
resistance and the fourth band d gives the percentage of accuracy called
tolerance. The resistance of carbon resistor R = (ab x 10c ± T %) Ω.
3. The table on left side provides the colour code for the carbon resistors :
PROCEDURE
1. Mark the given carbon resistors as R1,R2, R3.
2. Note the colour of first, second, third and fourth ring for each resistor.
3. Plug in the probes of the multimeter in appropriate terminals. Select the
appropriate range, short the other ends of probes and adjust zero. Turn
the terminal marked ‘Adjust’ such that the needle of the meter shows full
scale deflection and reads zero ohm.
4. Separate the metallic ends of the probes. Insert the resistor R 1 to be
measured in between the metallic ends of the two probes and read the
deflection of the pointer on the range selected.
5. Repeat the step 4 for other resistors R2and R3 each time selecting the
appropriate range and testing the zero.
6. Now convert using the colour code table, the values of resistors in ohms
and write their values with tolerance.
(b) D.C. Voltage
1. Select a D.C. source of potential difference, 6 V battery eliminator or a
battery.
2. Plug the probes black in com and red in +.
3. Select D.C. volt, by turning the selector switch to range 10 V D.C. volts,
4. Touch and press other ends of probes such that red is on battery terminal
marked + and black on and not the reading.
5. Insert red probe in terminals marked 4 V, 2 V in succession and note
readings.
(c) A.C. Volts
1. Turn the selector A.C. (200 Volt).
2. Touch and press the probes other ends to two terminals of A.C. source of
potential drop and note the reading.
3. Use red probe in terminals 4 V and 2 V in succession and record the
reading.
(d) Continuity of given circuit
1. Set the selector switch to ohm, range MΩ.
2. Touch and press the ends of probes at A and B, full scale deflection
indicates continuity.
3. Similarly check in succession the continuity between terminals B and C
and terminals C and D.
INFERENCE
1. The measured values by multimeter match with decoded values of
resistors.
2. A.C. and D.C. voltages marked on voltage sources match with voltage
measured by multimeter.
PRECAUTIONS
1. Instructions for handling the multimeter should be gone through
thoroughly as it is a very handy instrument and is likely to get damaged if
carelessly or ignorantly used.
2. Select the appropriate parameter current, voltage or resistance to the
measured and set it on appropriate range.
3. If range of the parameter measured is not known, start with maximum.
For measuring V, never connect more than maximum 600
THINGS TO BE WRITTEN ON LEFT HAND SIDE
OBSERVATION
TABLE FOR MEASURING RESISTANCE
Sl Resistanc Colour of rings R in Ω R Differ
no e used 1 2 3 4 measured ence
In Ω
1 R1 Yellow Violet Red Gold 4700 4670 30
2 R2 Brown Black Brow Gold 100 100 0
n
3 R3 Red Red Oran silver 22000 22200 200
ge
TABLE FOR MEASURING AC/DC VOLTAGE
Name of Sl no Voltage between Voltage Difference
source of emf terminals V0 measured by V-V0
(volts) multimeter
(volts)
‘V’(volts)
DC source 1 6 5.8 0.2
2 12 12 0
AC source 1 6 5.8 0.2
2 220 230 10
TABLE FOR CONTINUITY TEST
Sl no Device Resistance shown Conclusion
by multimeter
1 Cartridge fuse infinity There is a
discontinuity
2 Slide wire bridge 5Ω Continuous
3 Copper wire 5Ω Continuous
