This document provides instructions for an experiment on connecting lamps in series. It explains that when lamps of different wattages (e.g. 60W and 40W) are connected in series, the lower wattage lamp will glow brighter. This is because the resistance of the 40W lamp filament is higher, so it receives a higher voltage from the 240V power source. The document outlines the theory, apparatus needed, procedures for connecting same and different wattage lamps, and has students observe and draw their own conclusions.

1. Maharashtra Institute of Technology,
Aurangabad
LABORATORY MANUAL
Practical Experiment Instruction Sheet
EXPERIMENT TITLE : Concept of series lamp.
EXPERIMENT NO.6: MIT(T)/ETC/Basic Electrical Engineering /Manual No.1
FY(All) DEPARTMENT: Electronics & Telecommunication Engineering
LABORATORY : Basic Electrical Engineering Location Part I Page 33
Aim: Concept of series lamp.
Apparatus: 1. Wires 2. Switches 3. Plugs and Sockets 4. Fuses 5.Lamps 6. Multimeter
Theory:
While connecting two lamps in series there are two possibilities. Both lamp can have same wattage or
different wattage. The lamp having less wattage has more resistance and vice-versa. If the two lamps
of 60 watt and 40 watt are connected in series, 40 watt bulb will glow brighter. This is because the
resistance of the bulb filament will be in the ratio of 2:3. that means if the resistance of 60 W lamp is
2R then that of 40 W lamp will be 3R. When voltage of 240 volt is applied. The voltage across 40 W
bulb will be Current x 3R. If I is the current passing through both the bulbs the voltage across 40 W
will be I x 3R and across 60 W bulb would be I x 2R. Thus voltage across 40 watt bulb would be 144
volts and across 60 W bulb it would be 96 volts.
Voltage = 240 volts
Watts = 40 watt and 60 watts
R60 = 240×240/60= 960 ohms R40 = 240×240/40= 1440 ohms
Total of R60 + R40 = 960 + 1440 = 2400 ohms for series circuit
Amps = 240/2400 = 0.10 amps flowing through both 40w and 60w
watts = I²x R
watts for 60 watt = I²x R = 0.10² x 960 = 0.01×960 = 9.6 watts
watts for 40 watt = I²x R = 0.10² x 1440 = 14.4 watts
Therefore 40 watt is brighter. Another fact that helps to understand what you see is that the visible
light that comes out depends very strongly on how hot the filament gets.
Prepared By: Mr. S.S. Chate Approved By: Dr. G.S. Sable

2. Maharashtra Institute of Technology,
Aurangabad
LABORATORY MANUAL
Practical Experiment Instruction Sheet
EXPERIMENT TITLE : Concept of series lamp.
EXPERIMENT NO.6: MIT(T)/ETC/Basic Electrical Engineering /Manual No.1
FY(All) DEPARTMENT: Electronics & Telecommunication Engineering
LABORATORY : Basic Electrical Engineering Location Part I Page 34
The light that comes out will mostly be invisible infrared. The barely visible 60 W bulb looks pretty
reddish, not white, because the filament isn't hot enough to give the visible spectrum.
Wiring Diagram
Procedure :
1. Collect the required apparatus.
2. Connect the lamps(of same wattage) and the switch as shown in the circuit diagram.
3. Check the connections with the help of multimeter.
4. Operate the lamps using the switch.
5. Now replace one of the lamps with that of different wattage.
6. Operate the lamps using the switch. Observe status of lamps.
Conclusion: Write your own conclusion.
Prepared By: Mr. S.S. Chate Approved By: Dr. G.S. Sable