Problem 1:Incandescent Lamp

By Igor K.Liam N.Alex T.

Aim 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.

Hypothesis 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.

Materials 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

Method (1st part)

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.

Method (1st part)

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:

Method (1st part)

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.

Method (2nd part)

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

Method (2nd part)

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 12V6. Record its brightness periodically.

Results (1st part)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

Results (2nd part)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)  

Conclusion According to results, the 10W light

bulb did shine brighter than two 5W (in parallel) ones at different voltages. The hypothesis was supported.

Conclusion 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:

Conclusion 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.

Conclusion 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)

Conclusion From these few data points, it is clear

that the higher the supplied voltage is, the shorter time light bulb will live for.

Theory 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.

Evaluation/ErrorsThere 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.

Evaluation/Errors 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.