Transcript Problem 1: Incandescent Lamp

By Igor K.
Liam N.
Alex T.
 To
investigate whether one 10W light
bulb shines better than two 5W bulbs.
 Explore how a small change in voltage
will affect light emission and a light
bulb’s lifetime.
 1st
part:
The difference would be so tiny it won’t
be noticeable to a human eye, but it
would be present.
 2nd part:
If the voltage is higher, then the life of the
light bulb would decrease.
 10W
light bulb (3x)
 5W light bulb (6x)
 Ammeter
 Voltmeter
 Photometer (lightmeter)
 Alligator clips
 Power supply (+26V)
 Timer
 Camera
 Box that can isolate the external light
1. Get all the equipment ready.
2. Make the following circuit:
3. Place the photometer 5cm away from the
light bulb.
4. Turn the power supply on at 6V.
5. Write down the brightness.
6. Switch the power supply to 8V and
measure the brightness.
7. Switch the power supply to 10V and
measure the brightness.
8. Write down all results from part 4-7 in a
suitable table.
9. Now, make another circuit, which
diagram looks like the following:
10. Place the photometer next to light
bulbs so that it is 5cm away from each.
11. Do steps 4-8 with a newly made circuit.
7. Wait for the light bulb to blow.
8. Record the time taken on a suitable
table.
9. Replace the light bulb and turn the
power supply to 20V.
10. Wait for the light bulb to blow and write
down the suitable results
1. Get all the equipment ready.
2. Make the following circuit:
3. Place the photometer 5cm away from the
light bulb (optional).
4. Make sure the camera is ready.
5. Turn the power supply to 12V
6. Record its brightness periodically.
Wattage
Voltage (V)
Brightness (lx)
10W
6
70
10W
8
1,046
10W
10
4,329
10W
12
10,913
5W+5W
Parallel
6
48
5W+5W
Parallel
8
98
5W+5W
Parallel
10
150
5W+5W
Parallel
12
1,323
Voltage (V)
Time (min)
Brightness (lx)
20
0
14,273
20
1:00
8,866
20
2:00
8,076
20
3:00
7,867
20
4:00
7,212
20
5:00
6,420
20
6:00
4,417
20
7:00
1,195
20
8:00
1,079
20
8:41
922
21 -> 24 -> 25
8:42
20
15:36
18
15+
12
120,000:00 (2,000 hours)
 According
to results, the 10W light bulb
did shine brighter than two 5W (in
parallel) ones at different voltages. The
hypothesis was supported.
 This
means is that more light would be
‘focused’ at one point with the 10W bulb,
and only at a particular point with two 5W
bulbs, just as this diagram shows:
 As
a real life example, we can imagine a
room lit with a single central lamp of
120W, and then imagine the same room
lit by two 60W bulbs separated by a few
meters.
The illumination of the room will be more
even with the 60W bulbs but the single
120W bulb will include an area of higher
brightness than exists in the room when it
is lit by the 60W bulbs.
 The
original lifespan of a 5W light bulb at
12V was originally 120,000 minutes
(2,000 hours). A small increase in
supplied voltage to 20V has resulted the
lifetime to reduce to 15:36 minutes (7,692
times shorter). An increase to 24V has
resulted the lifetime to go down to 8:42
minutes (14,252 times shorter)
 From
these few data points, it is clear that
the higher the supplied voltage is, the
shorter time light bulb will live for.
 Why
does the light bulb blow?
The incandescent light bulb contains a thin
coil of tungsten called a filament. When
electric current flows through it, it
produces heat. When any metal becomes
this hot it combines with the oxygen in the
atmosphere and burns up.
There have been a lot of factors that affected
the results of this experiment. Some of them
were kept constant whilst it was impossible
for others to do so.
For example:
 Exact distance between a light bulbs at
different stages of the experiment.
 Positioning two 5W light bulbs so that they
are working ‘on the same level’.
 Original temperature of the bulb and how
used it is in the 1st place.
 Placing
the photometer on an exact angle
for different parts of the experiment.
 Readings off the timer/photometer
Next time, to make sure these things do not
happen, each of the parts will be repeated for
more than 3 times to get more accurate
results. Some new appropriate technology
might be used to ensure everything is kept
constant.