Name: ______________________________ Grade & Sec.:___________ Score:_________
Teacher:____________________________ Date:___________________ Rating:_________
Activity 1
Light sources: Langis kandila or lampara
Objectives
In this activity, you should be able to:
1. construct a simple photometer;
2. determine which chemical substance produce the brightest light; and
3. infer that brightness of light is dependent on the distance of the
source.
Materials Needed
an electric glow lamp (Small lamp is needed)
candle - weighing 75 grams
wedge with sloping surfaces (sharp angle about 60° to 70° that serve as
the photometer (made of white wood or paper)
langis kandila or lampara
variety of vegetable oil (about 5)
aluminum pie containers or small clay pots
cotton string for wick
set of books or tripod that will serve as platform for Diwali lights
Procedure
Part 1: Improvised Photometer
Arrange the electric glow lamp,
the candle and the wedge as
shown on the right. Make sure
that you do this activity in a
dark room for good results.
Illuminate the side “A” of the wedge by the lamp and side “B” by the
candle. In general the lamp side will look brighter than the other.
Move the wedge nearer to the candle to a spot at which you as an
observer, looking down on the two surfaces of the wedge (from “C”) cannot see
any difference between them in respect of brightness. (They are then equally
illuminated; that is to say the candle light falling on “B” is equal in intensity to
the electric light falling on “A.”)
Calculate the power of the lamp relative to the candle. (E.g. If both side of
the wedge showed equal illumination when it is about 200 cm from 1, and 50
cm from 2, the distances are as 4 to 1. But as light falls off according
to the square of the distance: (200)2 = 40 000 and (50)2= 2 500 or 16 to 1.).
Thus the candle-power of the lamp is 16.