Lower Secondary Science

[Mr Oh Ming Yeo]

Dear Physics Students,


Check out fuchunphysics.wordpress.com

This blog contains teaching videos for Physics O’ Level syllabus.
Chapters uploaded include:
1) Measurements
2) Kinematics
3) Dynamics
4) Mass, Weight and Density
5) Turning Effect of Force
6) Energy, Work and Power
7) Pressure
Kinetic model of matter

The teaching videos for the remaining chapters will be posted soon.

[happyluckymom]

This thread has been very informative. Thanks all!

[Verysuperkiasu]

Which of the following statements is true?


A)Bacteria cannot form spores
B) Fungi can only reproduce sexually.
C) All viruses have the same capsid symmetry.
D) Protocists like Amoeba and Paramecium are motile.

Answer : D. Why?

2) Object X has a melting point of 150 deg C and a boiling point of 350 deg C. In which of the following conditions does object X have the lowest density?
A) Object X at 0 deg C C) Object X at 350 deg C
B) Object X at 349 deg C D) Object X at 351 deg C

Ans : D. Why?

3)Why do telephone wires in some countries snap on very cold nights?
A) The telephone wires expand when temp is low.
B) The wires were not given enough slack when they were first installed?
C) The wires were given too much slack when they were first installed?
D) The wires reached their melting point on cold nights.

Ans: B. I can understand B if they mention wires snap on hot days, but on cold nights, shouldn’t wires contract? If so, why should they snap on cold nights?

[kurosaki]

Hi, can anyone explain how to answer this question? Many thanks!


State the colour of the objects when they are placed in different colours of light.
Colour in white light\tColour in cyan light\tColour in red light
a) Green\t\t
b) Yellow\t\t
c) Magenta\t\t
d) White \t\t
e) Blue

[Dr.033430Daniel]

Colour in White light/\tColour in cyan light/\tColour in red light

a)Green\t / Green / Black
b)Yellow\t / Green / \tRed
c)Magenta\t / Blue / \tRed
d)White\t / Cyan / \tRed
e)Blue\t
\t


There are 3 primary colors: Red, Green and Blue. The secondary colors contain two of the three primaries:

Yellow contains Red and Green
Cyan contains Green and Blue
Magenta contains Red and Blue.

White light contains all 3 primary colors.

a)So if something is green in white light then it reflects only one of the primary colors. Cyan contains green and blue – the green is reflected and the blue is not. Under red light the green object will look black, since no light is reflected. There is no green within red.

b)If something is yellow in white light, that means it reflects red and green but not blue. Cyan contains green and blue. So it will reflect only the green. Under red light it looks red since yellow reflects red. There is no green for it to reflect under red light, so it does not look yellow anymore.

c)If something is Magenta in white light that means it reflects red and blue but not green. Under Cyan light it will reflect only the blue and under red light it will reflect the red.

d)If something is white under white light it reflects everything, so whatever comes in, gets reflected.

I’ll let you do the last one……

I have a nice animation that I do in class to show all the colors on a big screen. The funny part about this subject is that many of the assessment books are printed in black and white – it’s much clearer when you can actually see the colors.

I just posted a color image at my website. You can see it here…. http://www.physicsandcalculus.com/2012/1666

If you have a color printer, just print out that picture and then use it as a reference for answering these questions and it should make things a lot easier.

[Dr.033430Daniel]

Answers in italics.....

Verysuperkiasu:

Which of the following statements is true?

A)Bacteria cannot form spores
B) Fungi can only reproduce sexually.
C) All viruses have the same capsid symmetry.
D) Protocists like Amoeba and Paramecium are motile.

Answer : D. Why?

Saying they are motile is just a fancy way of saying they can move around. Both Amoeba and paramecium live in water and swim around.

2) Object X has a melting point of 150 deg C and a boiling point of 350 deg C. In which of the following conditions does object X have the lowest density?
A) Object X at 0 deg C C) Object X at 350 deg C
B) Object X at 349 deg C D) Object X at 351 deg C

Ans : D. Why?

D would be a gas and the gas state has lower density than liquid or solid. Just as steam is less dense than liquid water.

3)Why do telephone wires in some countries snap on very cold nights?
A) The telephone wires expand when temp is low.
B) The wires were not given enough slack when they were first installed?
C) The wires were given too much slack when they were first installed?
D) The wires reached their melting point on cold nights.

Ans: B. I can understand B if they mention wires snap on hot days, but on cold nights, shouldn't wires contract? If so, why should they snap on cold nights?

B seems OK - by slack they mean extra length. If the wire contracts and there is no extra length it snaps. There are gaps in the MRT tracks so that when it is hot and the tracks expand they have room to expand. So heat a metal and it needs room to expand, cool a metal and it needs some slack.

[Verysuperkiasu]

Dr.Daniel:

Answers in italics.....


2) Object X has a melting point of 150 deg C and a boiling point of 350 deg C. In which of the following conditions does object X have the lowest density?
A) Object X at 0 deg C C) Object X at 350 deg C
B) Object X at 349 deg C D) Object X at 351 deg C

Ans : D. Why?

D would be a gas and the gas state has lower density than liquid or solid. Just as steam is less dense than liquid water.

.[/i]

[/quote]

Thank you....Dr Daniels...

But with regards to qn 2, just wondering if C is possible. Obj X at 350 deg C is still gaseous state? Or partially liquid partially gaseous?

[Dr.033430Daniel]

Sounds like they mean to imply that 350 would be liquid boiling, like water at 100C. One could argue also that the hotter the gas the lower the density (the principle behind hot air balloons).

[Verysuperkiasu]

Dr.Daniel:

Sounds like they mean to imply that 350 would be liquid boiling, like water at 100C. One could argue also that the hotter the gas the lower the density (the principle behind hot air balloons).

thanks

[Verysuperkiasu]

Hi I'm using my mom's account to ask a question: Are algae considered plants or protoctista? I know that blue-green algae are considered monera but what about the other types of algae? Thanks in advance