10. Illumination of the surface varies directly as
the cosine of the angle between the normal to
the surface and direction of incident light.
Normal surface Inclined surface
Lambert’s Cosine Law
19. Depending upon the wattage and voltage, the
diameter of a tungsten lamp filament may be as
small as 10 microns. This may be compared with
diameter of human hair which is about 60
microns.
The light spectrum of an incandescent lamp is
continous it contains all the colours but contains
relatively excess of red and yellow radiations and
less of blue and violet radiation.
The light output of an incandescent lamp various
from about 10 lumens per watt in the small
wattage lamps to 18 lumens per watt in the high
wattage lamps
Incandescent Lamp
20. High wattage lamps are filled with a mixture of
nitrogen and argon to retard the evaporation of
the tungsten filament. In low wattage lamps air is
evacuated to prevent heat loss by convection and
conduction and to prevent oxidation of the
filament
It causes increase in life of filament
Blackening of the lamp shell is due to the
depositsof tungsten vapour
The light output decreases gradually with use.
The total depreciation of light output is about
15% over the useful life.
Incandescent Lamp
21. It consists of a tungsten filament T placed in
a glass cover G . The filament is supported on
wire hooks fixed on a glass stem (S) and is
normally in the helical or coiled form.
This reduces the surface area of the filament
exposed to gas and thereby reduces the heat
loss and also it reduces space requirement
for large length of filament
Incandescent Lamp
23. Advantages
Simple in construction, easy to install and
maintain
Initial cost is less and it starts
instantaneously
Low efficiency and a short life
Vibrations very much shortens the life of
lamp
Care is needed in mounting
Frequents starts and stops has no effect on
the life of the lamp
Incandescent Lamp
24. Calculate the total flux from the lamp having
mean spherical candle power of 35.
Mscp =35
Mscp = Total flux/4π
35 = Total flux/4π
Total flux =440 lumens
Incandescent Lamp
25. A 250 Volt lamp has a total flux of
3000lumens and takes a current of 0.8 amp.
Calculate i) Lumens/watt ii) Mscp/watt
Wattage of lamp = 250 * 0.8 = 200 watts
Lumens/watt = φ /w = 3000/200 = 15
Mscp/watt =240/200 = 1.2
Incandescent Lamp
32. 1. Catridge Fuses are used to protect electrical aplliances
such as motor air conditions, pumps, refrigerator where
high V & I ratings are required. They are available upto
600A & 600V ac & widely used in industries, commercial &
home distribution panels.
2. Blade Type Fuses comes in plastic body and two metal
caps to fit in the socket. They are used in automobiles for
wiring & short circuit rupture capacity
3. High Rupturing Capacity(HRC) fuses is the
maximum current that can safely be interrupted by the
fuse.
HV HRC Fuses used as cable feeders, distribution T/f’s
and are also used for short circuit protection in high
voltage switch gear for 50 Hz to 60Hz frequency range.
Applications of fuses
34. 1. Wire or Strip Earthing
2. Rod Earthing
3. Pipe Earthing
4. Plate Earthing
1. Wire or Strip Earthing is applied at the
places (rocky soil) where it is difficult to dig
pits of desired depth. Usually a copper wire of
5SWG of enough length is buried in horizon
trenches of depth.
Different Methods of
Earthing
35. 2. Rod Earthing is used at sandy soil. Since
excavation is not required it is cheaper. A solid rod of
galvanised iron of diameter 1.9 cm is laid vertically
into the earth upto a depth of 200cm to 300cm. The
conductor is tied to the rod with small clamps.
3. Pipe Earthing is the common method of earthing
done using G.I of diameter 3.8cm. A pit of about 40
cm square area and 4 to 5 mt depth is dug in the soil.
To increase the dampness and moisture, charcoal and
salt are filled in the pit in alternate layers upto about
two metres from bottom. Earth pipe can be protected
from mechanical damage by covering it with cement
concrete work. A funnel with mesh can also be
provided to pour water.
Different Methods of Earthing
37. Neutral Wire:
Current is given through a wire called live
wire and given back through the neutral wire
To carry unbalanced load current
Neutral is a current carrying conductor
Collector for current
To return the current from appliance back to
the load centre
It will help to complete the circuit back to the
source of power.
Difference between neutral
wire and earth wire
38. A safety wire to stop the appliance becoming live.
Earthing acts as a sink for unwanted voltages and
currents
Earth wire is connected locally to ground
Earthing provide safety and protection for use
Earth in a mains electrical wiring system is a
conductor that provides a low impedance path to
the earth to prevent lazardous voltages from
appearing on an equipment
Earthing is to connect a point of the circuit to
ground literally to ensure zero potential in it
Difference between neutral
wire and earth wire
