Sec 2 Science (Electricity)
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Got 1 qn 2 ask:
The tungsten filament of an incandescent light bulb is coiled so as to
(a) increase the amount of current flowing through the filament so that the bulb is brighter
(b) increase the total surface area of the filament so that more light can be emitted
(c) increase the resistance of the filament so that more heat can be generated
(d) decrease the resistance of the filament to allow a larger current
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My answer is C i guess but my physics sucks
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(a) Nonsense, current have nothing to do with coils, use a stronger dc or ac source or increase resistance of wire, plus see part (c), V = IR, when R increase, V constant, I decrease
(b) Hmm....okays....but this is not scientific saying
(c) According to resistivity formulae:
Resistance = (Resistivity in a object -- constant in this qnsX Length ) / surface area
When length is increase by coil, resistance increases, more resistance means less electrons can move so easily, therefore, causing more heat to be generated, become brighter...
C seems okay and the best answer but it still lack the brightness part----
(d) no....see part (c)
So best ans is (c) but still 4 option seem not fully right..
eagle or other people pls help....
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below
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Originally posted by Darkness_hacker99:
The approach is:
1) What is the purpose of the light bulb? Provide light.
2) Difference between coiled and uncoiled? Light scattered differently.The assumption made in this question such that
i. votage, current, resistence, other paramenters unchange.
iii. only difference comparision is coiled and uncoiled. as shown in my diagram (look out for it)Using elimination method, option (d) will be out. Increase in length, increases the resistence. - as mentioned by SBS n SMRT.
The answer is not option (c), as the main purpose of a light bulb is to produce light. Incandescent light bulb, to me, is not an energy-saving light bulb. Hugh amount of energy is lost as heat.
Option (a) is not true too. As mentioned by SBS n SMRT, "current have nothing gotta do with coils". Actually it has, but it's dependant on the source of the electricity.
Option (b) seems to be the correct on after analyzing and reasoning.
a - coiled
b - uncoiled.
Summary:
Coiled filament tends to be emits more light due to the surface area to length dimension compacted in the coiled as compared to filament stretch straigth.Hypothesis generated: No matter how long you extend figure b, the light given off in terms of brightness (comparison with coiled vs uncoiled) will never exceed figure a.
Option (b) seems to be the more 'right' answer.
Gees.. this sec 2 physics question is general.... I didn't see any quantitatives in this questions...
comments and opinion appreciated. Thank you.
Regards,
Chin Seng. -
Answer is C
Such a light bulb can be seen in chicken rice stalls to provide heat to the cooked chicken so that it can be served warm to you. It is also use in incubators to provide heat to incubate the eggs.
Not necessary used for light only ;)
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O.o" I learned something...
Yea! Parsa Malam stall also uses such lights! no wonder.... their food still warm after so long...
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Originally posted by Dixon999:
Got 1 qn 2 ask:
The tungsten filament of an incandescent light bulb is coiled so as to
(a) increase the amount of current flowing through the filament so that the bulb is brighter
(b) increase the total surface area of the filament so that more light can be emitted
(c) increase the resistance of the filament so that more heat can be generated
(d) decrease the resistance of the filament to allow a larger current
filament is "coiled" to pack more tungsten in light bulb. B. to increase total surface area for photon emission.
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Originally posted by Darkness_hacker99:
O.o" I learned something...
Yea! Parsa Malam stall also uses such lights! no wonder.... their food still warm after so long...
pasar malam used these light more on to attract customers, not quite in physical manner