Physics MCQ questions.
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Hi, I have some problems here. Please help me.
1. X and Y are lamps with filaments made from the same material.
The filament of lamp X is thicker and shorter than that of lamp of Y.
When connected to the mains and switched on, which is the brighter lamp and which lamp has larger resistance? (Q25 Nov/03)
My teacher's answer is both Y. However, the answer in SAP's Past Year Question is X and Y respectively.
Which one is correct? If my teacher is correct, then I really don't understand, according to P = V²/R (I assume the voltage is constant, since it is connected to mains), the lower the resistance the higher the power dissipate, thus brighter?
2. The diagram shows a strip of paper tape that has been pulled under a vibrating arm by an object moving at constant speed. The arm is vibrating regularly, making 50 dots per second. (Q5 Nov/06)
What was the speed of the object?
A. 2.0cm/s B. 5.0cm/s C. 100cm/s D. 200cm/s
I have no idea about this...
3. (A random question) If you place 100cm³ of liquid water into freezer, will you get a 100cm³ ice cube?
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Originally posted by ladingdong:
Hi, I have some problems here. Please help me.
1. X and Y are lamps with filaments made from the same material.
The filament of lamp X is thicker and shorter than that of lamp of Y.
When connected to the mains and switched on, which is the brighter lamp and which lamp has larger resistance? (Q25 Nov/03)
My teacher's answer is both Y. However, the answer in SAP's Past Year Question is X and Y respectively.
Which one is correct? If my teacher is correct, then I really don't understand, according to P = V²/R (I assume this is parallel circuit, since it is connected to mains), the lower the resistance the higher the power dissipate, thus brighter?
2. The diagram shows a strip of paer tape that has been pulled under a vibrating arm by an object moving at constant speed. The arm is vibrating regularly, making 50 dots per second. (Q5 Nov/06)
What was the speed of the object?
A. 2.0cm/s B. 5.0cm/s C. 100cm/s D. 200cm/s
I have no idea about this...
3. (A random question) If you place 100cm³ of liquid water into freezer, will you get a 100cm³ ice cube?
Firstly i like the way you post your qn.
1) i think it is theory that the light is caused by resistance. I may be wrong. btw, tungsten material is used as filament because it is hard to melt even with high temp.
2)it takes 1/50 sec from one dot to another. So 21 dots means 20 spaces and thus 2/5 sec.
speed = 0.2m/ (2/5)
3)no. For water it is special. The volume actually increases when it turns from liquid to solid, contrary to the particle theory. Pros: i am curious to know why.
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1. Resistance R = pl/A
Since lamp X has a shorter filament length, l is lower.
Lamp X also has a thicker filament, hence A is larger.
Hence, when l decreases, and A increases, R is smaller for X.
Hence Y has a larger resistance.
If according to P = V^2/R, then X should be brighter right.
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1. X and Y are lamps with filaments made from the same material.
The filament of lamp X is thicker and shorter than that of lamp of Y.
When connected to the mains and switched on, which is the brighter lamp and which lamp has larger resistance? (Q25 Nov/03)
My teacher's answer is both Y. However, the answer in SAP's Past Year Question is X and Y respectively.
Which one is correct? If my teacher is correct, then I really don't understand, according to P = V²/R (I assume the voltage is constant, since it is connected to mains), the lower the resistance the higher the power dissipate, thus brighter?
This has been asked quite a few times.
You are correct. It's time to sack the teacher.
2. The diagram shows a strip of paper tape that has been pulled under a vibrating arm by an object moving at constant speed. The arm is vibrating regularly, making 50 dots per second. (Q5 Nov/06)
What was the speed of the object?
A. 2.0cm/s B. 5.0cm/s C. 100cm/s D. 200cm/s
50 dots = 1 s
1 dot = 1/50 s
10 dots = 10/50 s
s=d/t = 20/ 10/50 = 20 x 50/10 = 100cm/s
david your concept is wrong, you don't count by the spaces, you start counting the first dot as 0.
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1. X and Y are lamps with filaments made from the same material.
The filament of lamp X is thicker and shorter than that of lamp of Y.
When connected to the mains and switched on, which is the brighter lamp and which lamp has larger resistance? (Q25 Nov/03)
My teacher's answer is both Y. However, the answer in SAP's Past Year Question is X and Y respectively.
Which one is correct? If my teacher is correct, then I really don't understand, according to P = V²/R (I assume the voltage is constant, since it is connected to mains), the lower the resistance the higher the power dissipate, thus brighter?
Wait a minute... If you use P=I²R, you get Y as the brighter lamp.
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First question has been asked and discussed here (together with Garrick)
http://www.sgforums.com/forums/2297/topics/336112
The rest of the questions I look later.
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Originally posted by Peoplethinkimsarcastic:
Wait a minute... If you use P=I²R, you get Y as the brighter lamp.
It's connected to an a.c. mains switch. Thus constant voltage. So V^2/R applies.
For qn 2, there's 10dots for 20cm, so applying (cm/dots) * (dots/s) = (cm/s),
50 dots/s * (20 cm/10 dots) = 100 cm/s -
Originally posted by Garrick_3658:
david your concept is wrong, you don't count by the spaces, you start counting the first dot as 0.
actually it's the same if you count the spaces in between and counting the first dot as zero
Think about it
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Originally posted by ladingdong:
Hi, I have some problems here. Please help me.
1. X and Y are lamps with filaments made from the same material.
The filament of lamp X is thicker and shorter than that of lamp of Y.
When connected to the mains and switched on, which is the brighter lamp and which lamp has larger resistance? (Q25 Nov/03)
My teacher's answer is both Y. However, the answer in SAP's Past Year Question is X and Y respectively.
Which one is correct? If my teacher is correct, then I really don't understand, according to P = V²/R (I assume the voltage is constant, since it is connected to mains), the lower the resistance the higher the power dissipate, thus brighter?
2. The diagram shows a strip of paper tape that has been pulled under a vibrating arm by an object moving at constant speed. The arm is vibrating regularly, making 50 dots per second. (Q5 Nov/06)
What was the speed of the object?
A. 2.0cm/s B. 5.0cm/s C. 100cm/s D. 200cm/s
I have no idea about this...
3. (A random question) If you place 100cm³ of liquid water into freezer, will you get a 100cm³ ice cube?
Question 1 and 2 have been answered. I shall answer question 3
3. (A random question) If you place 100cm³ of liquid water into freezer, will you get a 100cm³ ice cube?
No. It will be larger.
Simple proof: Think about density of ice. The number of molecules of the water that freezes should remain the same, hence the mass of the ice cube is the same as the mass of the water being frozen.
Since ice has a lower density, hence it's volume must be higher.
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Originally posted by ladingdong:
Hi, I have some problems here. Please help me.
1. X and Y are lamps with filaments made from the same material.
The filament of lamp X is thicker and shorter than that of lamp of Y.
When connected to the mains and switched on, which is the brighter lamp and which lamp has larger resistance? (Q25 Nov/03)
My teacher's answer is both Y. However, the answer in SAP's Past Year Question is X and Y respectively.
Which one is correct? If my teacher is correct, then I really don't understand, according to P = V²/R (I assume the voltage is constant, since it is connected to mains), the lower the resistance the higher the power dissipate, thus brighter?
2. The diagram shows a strip of paper tape that has been pulled under a vibrating arm by an object moving at constant speed. The arm is vibrating regularly, making 50 dots per second. (Q5 Nov/06)
What was the speed of the object?
A. 2.0cm/s B. 5.0cm/s C. 100cm/s D. 200cm/s
I have no idea about this...
3. (A random question) If you place 100cm³ of liquid water into freezer, will you get a 100cm³ ice cube?
fact: water that is frozen into ice has bigger volume.
proof: observe when you take ice cube from your ice tray next time.
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Suggested reasons are that the hydrogen bondings in the water form dunno what structures resulting in expansion. Go read wiki or google.