physics help

last SG · 2008-11-05T20:50:41+00:00

i see, so what has that got to do with the question? is noting the brightness of the circuit a hard thing to do, and something that needs to be assumed? can'...

ZedNg SG

anyone pls?

http://img353.imageshack.us/my.php?image=ccf1105200800000rw0.jpg

http://img353.imageshack.us/my.php?image=ccf1105200800001ht7.jpg

Edit: Help display images

skythewood SG

thick means less resistance.

long mean more resistance.

ZedNg SG

i know but

half the diameter is 4 times the resistance rite?

skythewood SG

yah

eagle SG

i know but

half the diameter is 4 times the resistance rite?

Because resistance is indirectly proportional to area

and area is proportional to the square of the diameter

You should know the formula

R = pl/A

ZedNg SG

oh i saw it now

that question is area not diameter

but then the light bulb one leh?

eagle SG

Larger resistance will have brighter light because power used is more.

From here, you should be able to find that ans is either A or D.

Filament X is thicker (lesser resistance) and shorter (also lesser resistance), hence Y has higher resistance

Thus, answer is D.

ZedNg SG

but ur case is only if the bulb are connected in series,which is not stated(only say connected to mains)

but the bulbs are connected separately i.e diff circuit since they say connect to mains

Garrick_3658 SG

oh i saw it now

that question is area not diameter

but then the light bulb one leh?

Obvious A and C are out.

Connected to mains, means same voltage. So it's easier to use P=V^2/R to determine brightness.

So the one with the smaller R is brighter.

Answer: B

EDIT: I assume different circuit. I went through this question in Victoria School Prelim Paper before.

If it's same circuit, then V will be different. But current in a series circuit is same throughout. So use P=I^2xR

Answer: D (if same circuit in series)

If parallel, then it's B. Can figure?

ZedNg SG

my teacher say the ans is b but my teacher tend to give diff answer from the answer key. he like almost never agree with the tys ans key

EDIT: my teacher have the same explaination as garrick but my question is u should assume that is the circuit is separated?

Garrick_3658 SG

Ambiguous question. Pity we can't shade both.

ZedNg SG

this question also appear on last yrs paper

in the exact same way

so i dunno man

i am ****ing confused

skythewood SG

If everything else is the same,

smaller resistance ==> brighter bulb, since E = I^2Rt

solve accordingly

ZedNg SG

btw thx eagle for helping me with the pic

not too sure how to operate the functions

eagle SG

Garrick is right in his explanations

ZedNg SG

so assume or not assume?

that is the question

skythewood SG

here's what i think.

set up a series connection. insert bulb 1. note the brightness.

remove bulb 1. insert bulb 2. note the brightness.

Garrick_3658 SG

here's what i think.

set up a series connection. insert bulb 1. note the brightness.

remove bulb 1. insert bulb 2. note the brightness.

In physics, we don't do qualitative reading. It is too debatable. We do quantitative reading.

By the way the only way to measure light intensity is data logger, so bo bian do qualitative reading lor...

skythewood SG

In physics, we don't do qualitative reading. It is too debatable. We do quantitative reading.

By the way the only way to measure light intensity is data logger, so bo bian do qualitative reading lor...

what the hell is qualitative reading, and what has it got to do with the question?

is what i described wrong or fundamentally flawed? so the correct setup is to connect both bulbs at the same time?

Garrick_3658 SG

what the hell is qualitative reading, and what has it got to do with the question?

is what i described wrong or fundamentally flawed? so the correct setup is to connect both bulbs at the same time?

Qualitative reading is just to use your senses and ASSUME a result.

For example: Which is heavier, a stone or a feather?

If you say feather STRAIGHT AWAY, then it's qualitative reading. Prove? Hold and see which one heavier.

If you use an electronic balance and weigh them, THEN say it's feather, that's quantitative reading. Prove? The stone is 100g while the feather is 0.1g.

Back to question: Assume they are connected in DIFFERENT circuits, separately. For me, that is. Ask eagle to confirm maybe. He's the senior around here.