Q&A - PSLE Science

[Sun_2010]

Verysuperkiasu:

atutor2001:

[quote=\"Verysuperkiasu\"]
Oh, I see. So u mean even if the batteries are not connected properly, the current is still able to flow through? Just that the voltages is zero?....TIA

Your statement is not correct. The current can only flow if the voltage in one direction is higher than the other direction i.e. there is a net voltage in the circuit.

For example, if there are 5 batteries in one direction and 3 batteries in the opposite direction then there is a \"net voltage\" of 2 batteries (5 - 3 = 2). The brightness of the bulb is the same as a circuit with 2 batteries connected in series in the same direction.

If there are 5 batteries in one direction and 5 batteries in the opposite direction then there is a net voltage of 0 (5 - 5 = 0). The bulb will NOT light up because the net voltage is 0. The batteries are still conductors of electricity but NO current will flow because current can only flow if there is a \"net voltage\" from the batteries in the circuit.

sorry, I'm quite bad in understanding electricity. If batteries are conductors of electricity (then shouldn't electricity still flows) isn't flow of electricity = flow of current? that is, if batteries still can conduct electricity, shouldn't current flow as well?[/quote]Let me try to explain-

Current will flow only of there is a potential difference ie. voltage.

as atutor put it \"If there are 5 batteries in one direction and 5 batteries in the opposite direction then there is a net voltage of 0 (5 - 5 = 0). The bulb will NOT light up because the net voltage is 0. \"
In this case the net voltage is 0 so there is no current. Just like if you take a wire and connect both ends there will not be any current in it even though it is a conductor as there is no voltage.
For case 2 \"if there are 5 batteries in one direction and 3 batteries in the opposite direction then there is a \"net voltage\" of 2 batteries (5 - 3 = 2). \"
As there is a \"net voltage\" and the circuit is complete, there will be a flow of current .

[atutor2001]

Verysuperkiasu:

sorry, I'm quite bad in understanding electricity. If batteries are conductors of electricity (then shouldn't electricity still flows) isn't flow of electricity = flow of current? that is, if batteries still can conduct electricity, shouldn't current flow as well?

You may like to visualise it as that if there are 5 batteries in one direction and 5 batteries in the opposite direction then the end result is the same as if there is NO (0) battery in the circuit (5 - 5 = 0). NO current i.e. electricity will flow in a circuit that has NO battery connected. Hope it helps.

Thank you Sun_2010 for your help.

[Verysuperkiasu]

Thank you atutor and sun_2010 for your explanation. I understand now.

[Koky462]

I have an question on the method of reproduction from my son’s exercise.


x - Man, Frog, Polar bear\t\t
y - Yeast, Amoeba, Paramecium
\t
a)What is the main difference between the two methods of reproduction for X & Y?
b)Name the reproduction method under the sub-heading X.

[Selfan4ever.05005423]

Koky462:

I have an question on the method of reproduction from my son's exercise.


x - Man, Frog, Polar bear\t\t
y - Yeast, Amoeba, Paramecium
\t
a)What is the main difference between the two methods of reproduction for X & Y?
b)Name the reproduction method under the sub-heading X.

b) External

[Selfan4ever.05005423]

Koky462:

I have an question on the method of reproduction from my son's exercise.


x - Man, Frog, Polar bear\t\t
y - Yeast, Amoeba, Paramecium
\t
a)What is the main difference between the two methods of reproduction for X & Y?
b)Name the reproduction method under the sub-heading X.

b) External

[Selfan4ever.05005423]

Koky462:

I have an question on the method of reproduction from my son's exercise.


x - Man, Frog, Polar bear\t\t
y - Yeast, Amoeba, Paramecium
\t
a)What is the main difference between the two methods of reproduction for X & Y?
b)Name the reproduction method under the sub-heading X.

b) External

[bestwishes]

Selfan4ever♥23:

Koky462:

I have an question on the method of reproduction from my son's exercise.


x - Man, Frog, Polar bear\t\t
y - Yeast, Amoeba, Paramecium
\t
a)What is the main difference between the two methods of reproduction for X & Y?
b)Name the reproduction method under the sub-heading X.

b) External

a) X: Sexual reproduction (involves 2 parents of opposite sexes; involves fertilisation)
Y: Asexual reproduction (involves a single parent; not involve fertilisation)

Frogs in X -- external fertilisation
Mammals in X -- internal fertilisation
Yeast in Y -- budding (a kind of cell division)
Amoeba & Paramecium in Y -- binary fission (a kind of cell division)

[Koky462]

Thank you Selfan4ever23 & bestwishes for your replies!

[elkniwt]

Hi,


Need some advises on this qn :

Which of the following is/are the correct functions of the trunk of a rain tree?
A. It transports water and mineral salts to all parts of the plant.
B. It keeps the plant upright.
C. It twines round a support to help the plant reach for more sunlight.
D. It transports food from the leaves to all parts of the plant.

(1) A only
(2) A and B only
(3) C and D only
(4) A, B and D only

The answer in answer key is (4). My dd’s questions are "is it correct to say the trunk transports food, isn’t it the phloem that does that?" And she also asks, if a qn asks for the function of a trunk, can she actually write "it transports food to all parts of the plant"??

Many thanks.