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Comments (4)
johnlittlephysics said
at 9:59 pm on Apr 8, 2014
Yi Xuan: If the question asks "Why is tungsten commonly used in light bulbs?", how should I answer with respect to tungsten's high resistance and the conversion of electrical energy to light energy?
johnlittlephysics said
at 10:00 pm on Apr 8, 2014
The key reason is tungsten has a very high melting point 3422 deg C, so it does not melt when the filament is very hot and bright.
References:
http://home.howstuffworks.com/light-bulb2.htm
http://scienceline.ucsb.edu/getkey.php?key=2548
johnlittlephysics said
at 8:17 pm on May 8, 2014
405 Celeste: Could I make a clarification on Current of Electricity? With reference to a circuit with two resistors in series with a battery,
1. is the amount of current flowing through the two resistors the same as they are in series, regardless of whether the resistance they possess is different or not?
2. Also, in a series circuit, how is emf split amongst resistors? Is it according to proportion? If so, does a resistor of greater resistance have great pd across its ends?
johnlittlephysics said
at 8:22 pm on May 8, 2014
1. When resistors are in series, the same current will flow through them. This is shown by ammeters placed at different points along the circuit showing the same current reading.
2. V = IR, where I is the same but R is different, V is directly proportional to R
The p.d. V across each resistor would be different depending on its resistance R, the greater its R, the greater its p.d. V.
If two resistors R1 and R2 are in series with a battery with e.m.f., and their p.d.s are V1 and V2, e.m.f. = V1 + V2
Also e.m.f. = IR1 + IR2 (same current I) = I (R1 + R2) = I R(effective)
so current I = e.m.f. / R(effective)
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