incandescent bulb

INCANDESCENT BULBPandav, Concollato, Johns,

Rahman

Aim Materials Method Results Discussion Conclusion

To (a) determine whether one 10 W light bulb shines better than two 5 W light bulbs, to (b) determine how a small change in supplied voltage affects light emission, and to (c) determine how a small change in supplied voltage affects a light bulb’s lifetime.

Aim


Controlled Independent Dependent

Distance between luxmeter and bulb

Types of bulbs used Light intensity (Lux)

Environment the bulb is in

Number of bulbs used

External lighting conditions

Voltage supplied to bulbs

Circuit used for each bulb

Variables involved


Materials and equipment


Materials and equipment

2 x 5 W incandescent lamp 1 x lux-meter

1 x 10 W incandescent lamp 1 x spectrometer

2 x 12 V power supply 1 x ruler

4 x voltmeter 1 x cylindrical cardboard tube

2 x ammeter Wires to connect the circuit

2 x variable resistor (rheostat) Access to a computer

4 x retort stand with clamp Access to a dark room


1. The following circuits were set up next to each other. For the first trial, only one 10 W light globe was set up, on one circuit. The other circuit remained open.

PART

A


2. A cylindrical tube was set up as follows, over the 10 W light bulb. The apparatus was held in place using a retort stand.

PART

A


This setup allowed us to keep the distance between the light bulb and the sensors constant.

PART

A


3. The luxmeter and spectrometer were both connected to a laptop, where SPARKvue was used to analyse data.

4. The brightness setting of the laptop was set to a minimum, and the screen was bent down and turned away from the apparatus so that it didn’t interfere with results.

5. The lights were turned off.6. The 10 W light bulb was turned on for one minute, and the

following data was recorded:• Light intensity over time• Light intensity of various wavelengths of the

electromagnetic spectrumPART

A


PART

A


7. For the second trial, two 5 W light globes were set up, one on the circuit on the left, and another on the right. The two circuits are identical.

PART

A


8. A cylindrical tube was set up as follows, over the two 5 W light bulbs, which were placed right next to each other.

PART

A


The same steps used for the single 10 W light bulb were repeated with the two 5 W light bulbs.

9. The luxmeter and spectrometer were both connected to a laptop, where SPARKvue was used to analyse data.

10.The brightness setting of the laptop was set to a minimum, and the screen was bent down and turned away from the apparatus so that it didn’t interfere with results.

11.The lights were turned off.12.The 5 W light bulbs were turned on for one minute, and the


electromagnetic spectrum

PART

A


PART

A

The following are the results obtained for the single 10 W light bulb.

NOTE: 70 is the standard deviation of the trial, which went for a minute.

Current (A) 0.751

Voltage across the power supply (V)

11.57

Voltage across the light bulb (V) 11.00

Mean light intensity (Lux) 1373 ± 70


PART

A

The following are the results obtained for the two 5 W light bulbs.

Left Right

Current (A) 0.372 0.366

Voltage across the power supply (V)

11.64 11.59

Voltage across the light bulb (V)

11.52 11.50



Part B continued on from Part A, using the same circuits.

For the single 10 W bulb:

1. After the single-bulb trial in Part A was finished, the resistance on the rheostat was increased in such a way that the voltage across the light bulb decreased by 0.5 V.

2. The lights were turned off.3. The 10 W light bulb was turned on for one minute, and the



PART

B


Part B continued on from Part A, using the same circuits.

For the two 5 W bulbs:

1. After the double-bulb trial in Part A was finished, the resistance on both rheostats was increased in such a way that the voltage across each light bulb was decreased by 0.5 V.

2. The lights were turned off.3. The 5 W light bulbs were turned on for one minute, and the



PART

B


PART

B


The following are the results obtained for the single 10 W light bulb after the voltage was decreased by 0.5 V.




PART

B


The following are the results obtained for the two 5 W light bulbs after the voltage was decreased by 0.5 V.




We performed some preliminary trials without the cylindrical tube first. The rest of the method was the same. The sensors were each held in place using retort stands and clamps.


Some preliminary trials were performed without the cylindrical tube first. The rest of the method was identical. The sensors were each held in place using retort stands and clamps.


There was a lot of variation in our results, because it was difficult to position the luxmeter at the same angle each time, using just the retort stands. This resulted in a large standard deviation.


The bulb(s) and the luxmeter were then fixed in place inside the tube, in order to eliminate this problem.


PART

A



Using these results, it can be seen that a single 10 W light bulb shines brighter than two 5 W light bulbs.




PART

A

The following are the results obtained for the single 10 W light bulb during the preliminary trials.

The following are the results obtained for the two 5 W light bulbs during the preliminary trials.

The results from the preliminary trials also indicate that a single 10 W light bulb shines brighter than two 5 W light bulbs.




PART

B


The following are the results obtained for the single 10 W light bulb after the voltage was decreased by 0.5 V.

This suggests that a decrease in voltage leads to a decrease in light intensity.




PART

B


The following are the results obtained for the two 5 W light bulbs after the voltage was decreased by 0.5 V.

This also suggests that a decrease in voltage results in a decrease in light intensity.




PART

C

The following is a suggested method for Part C.

1. Set up an external thermometer so that it is 1 cm away from a 5 W light bulb, and is pointing at the bulb’s filament. Use the same circuit outlined previously. The light bulb should be 5 W at 6 V.


PART

C

The following is a suggested method for Part C.

2. Gradually decrease the resistance of the rheostat, hence increasing the voltage supplied to the light bulb, until the fuse blows. Record the temperature at which the fuse blows.

3. Set up two identical 5 W bulbs, each with different voltages supplied to them. Leave these on continuously for 72 hours.

4. After the 72 hours have elapsed, measure the temperature of the filament of each globe to observe which globe is closest to the temperature at which the fuse blew in Step 2.

Steps 3 and 4 could be repeated to get a wide range of voltages, and hence see how each voltage affects the lifetime of the bulb.


A 10 W light bulb shines brighter than two 5 W light bulbs.

As the voltage supplied to a light bulb decreases, the intensity of the light it produces also decreases.


References

Woolf, L (n.d.). Seeing the Light: The Physics and Materials Science of the Incandescent Light Bulb. Retrieved on October 30, 2013 from , http://www.sci-ed-ga.org/modules/materialscience/light/index.html>

Cornell University (April 3, 2000). Light Source Spectra. Retrieved on November 2, 2013 from http://www.graphics.cornell.edu/online/measurements/source-spectra/index.html

Covington, E (n.d.). Early Incandescent Lamps. Retrieved on November 4, 2013 from <http://home.frognet.net/~ejcov/>

http://www.sci-ed-ga.org/modules/materialscience/light/index.html

http://www.graphics.cornell.edu/online/measurements/source-spectra/index.html




http://home.frognet.net/~ejcov/



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equipment2 x

spectrometer2 x

computer4 x retort

following data