Lower Secondary Science

[BoboPanda]

Hi Pasta Greely,

You may want to check out this topic thread yourself \"Secondary School Science\": http://www.kiasuparents.com/kiasu/forum ... =29&t=7748
You can see Dr. Daniel's replies to a lot of questions on Science and/or Physics questions by parents.

I have been following this topic thread to help my children. When any one of my children wants to take Science or Physics tuition, I will definitely go to Dr. Daniel coz I find his explanation very clear and easy to understand.

[Michaelia0816]

I have no idea what to do... Should I use v=ir formulae but idk how http://i61.tinypic.com/k0sh3r.jpg

[Dr.033430Daniel]

Michaelia0816:

I have no idea what to do... Should I use v=ir formulae but idk how http://i61.tinypic.com/k0sh3r.jpg

The voltage across YZ is the same as the voltage across WX. Both resistors have the same amount of current going through them. Current is never destroyed in circuits with resistors. Both these resistors are in the main path, so if they have the same resistance and same current, then using V=IR, they have the same voltage.

Voltage across YZ is 3.6 V

Voltage across XY must be the remaining voltage 9V – 3.6 – 3.6 = 1.8V

Also if you look at the equivalent resistance of the three resistors in parallel – it is 0.5 Ohms. You get that by taking 1/Re = ½ + ½ +1/1. So the same current going through half the resistance gives you half the voltage or 1.8 V.

The voltage across each 2 Ohm resistor is the same = 1.8V. For circuit elements in parallel, they have the same voltage across them.

The current at X is 3.6A. The same current that goes into the first resistor comes out of the first resistor.

The current at point Z is the same also = 3.6A

For the current through each 2 Ohm resistor, use V=IR. The voltage across the 2 Ohm resistor is 1.8V.
1.8V = I (2 Ohms)
I = 0.9Amps.

[Mary Joy]

Can someone help me with this physics question.... :thankyou:


http://i57.tinypic.com/a4t0y0.jpg\">

[Mary Joy]

http://i62.tinypic.com/2yv2a34.jpg\">


http://i57.tinypic.com/i3xvo7.jpg\">

Please help me with this question...Thanks

[dioprem]

Mary Joy:

Can someone help me with this physics question.... :thankyou:


http://i57.tinypic.com/a4t0y0.jpg\">

Not too much information given here, so I'm going to make the assumption that the M113 has to be afloat in pure water. In order for a body to float in a liquid, it needs to have a lower density as compared to the liquid. In the case of pure water, its density is 1000 kg/m3.

Since density = mass / volume,

1000 = 1.115 X 10^4 / volume

Hence volume = 11.15 m3

So the M113 would need a volume greater than that to stay afloat.

Hope this helps!

P.S The print is a little small so the value I used for the mass of the M113 could be wrong, but the principle is still the same.

[Dr.033430Daniel]

Mary Joy:

http://i62.tinypic.com/2yv2a34.jpg\">


http://i57.tinypic.com/i3xvo7.jpg\">

Please help me with this question...Thanks

According to the graph, when the light intensity is zero then the number of oxygen bubbles is zero. Since oxygen is a byproduct of photosynthesis, this shows that light is essential for photosynthesis to occur.

What is not 100% clear from the question is whether there was actually a data point taken with 0 light intensity. It seems so since both graphs are extended down to 0 light intensity. To cover any uncertainty in this, you could add.....

The entire apparatus could be covered to ensure zero light intensity and then the volume of oxygen collected could be measured before and after to confirm that no oxygen is produced in the dark.

[Techmummy]

Can anyone help me with q 27

Thanks in Advance

[S_Mummy]

Please help. Why is b. incorrect.


Which of the following substances is made up of four elements?
a.\t C5H7COOC2H5
b.\tNH4NO3
c.\tK2Cr2O7
d.\tNaHCO3

[Dr.033430Daniel]

Wimpy Kid:

Please help. Why is b. incorrect.


Which of the following substances is made up of four elements?
a.\t C5H7COOC2H5
b.\tNH4NO3
c.\tK2Cr2O7
d.\tNaHCO3

For choice b There is Nitrogen, 4 Hydrogens, then Nitrogen again, then 3 Oxygens. Since Nitrogen is repeated it only counts as one element.

By the way an element symbol always has either one capital letter or a capital and a lower case letter. So an element will never have two capital letters in it's symbol. Sometimes chemists do write chemical formulas where an element is repeated more than once.

Choice d has Sodium, Hydrogen, Carbon and Oxygen - 4 elements.