Lower Secondary Science

[sparks]

Anyone has recommendations for good assessment books for biology? My dd will be doing her Os next year. Appreciate your recommendations pls. thanks.

[toofree]

sparks:

Anyone has recommendations for good assessment books for biology? My dd will be doing her Os next year. Appreciate your recommendations pls. thanks.

I dun take bio, but I saw some of my frens using marshall cavendish Perfect Guidebook for bio. But they didn't use the same title for Physics and Chemistry as they say the books failed as they are not very good and very repetitive.

[toofree]

Crester:

Can any 1 tell me how to find the Chemical Formula for Sulfuric Acid and ammonia?

Thanks.

The chemical formulas are:

1) Sulfuric Acid: H2SO4
2) Sulfurous Acid: H2SO3
3) Ammonia Gas: NH3
4) Aqueous Ammonia: NH3.H2O or NH4OH

Be careful what the question is asking for, my teacher always say.

To get the chemical formul for sulfurous acid, you need to noe that hydrogen ion is H+, and the sulfate ion is SO4^2-. Then you do the cross.

For ammonia gas, it's a covalent compound. Nitrogen needs to gain three electrons, but hydrogen can only share one electron. So we need three hydrogen atoms to one nitrogen atom, resulting in NH3.

[toofree]

jetstar:

Do you by chance also know of any way to remember the components of crude oil and the solubility table?

Thank you!

Hmm... My reference book has quite a lot of useful ways to remember things. I am using Smashing Exams - Sec 3 & 4 Chemistry and Physics.

For example, to remember the crude oil, it was written in the book:
Pink Panther Never Kisses Dirty Looking Boys (Petroleum gas, petrol, naptha, kerosene, diesel, lubricating oil, bitumen)

To remember solubility table, you can use:
SPA (Sodium, Potassium and Ammonium salts are all soluble)
Lower Secondary Basic Chinese Language (Lead(II) chloride, Silver chloride, Barium Sulfate, Calcium sulfate and lead(II) sulfate are insoluble)...

There are also other ways to remember things like mass = density x volume, using Monkey Drives Van.

I have been using the books since secondary 1. Been doing ok, without tuition too. haha.

[sparks]

toofree:

I dun take bio, but I saw some of my frens using marshall cavendish Perfect Guidebook for bio. But they didn't use the same title for Physics and Chemistry as they say the books failed as they are not very good and very repetitive.

:thankyou: toofree!

[Dr.033430Daniel]

jetstar:

Hi Dr Daniel,


Could you kindly help my son with the following question:

http://i42.tinypic.com/xn7sc7.jpg\">

Thank you!

Choice A.

Sorry for the delayed reply. It’s been crazy lately with lots of students joining up to prepare for exams.

When you put iron inside the solenoid, you make it stronger. Moving the iron toward the solenoid would have the effect of increasing the magnetic field inside the solenoid on the way in. The solenoid, acting as an inductor, would oppose the change in the magnetic field. It would set up a current in the opposite direction as the one from the battery which is causing it's original magnetic field. So the first part of the graph should show a dip in the current. For the iron inside the solenoid, the magnetic field would be constant inside. This would produce no reaction from the solenoid. The current is determined by the resistance of the wires since it is a DC current. So I would expect the current to remain the same while the iron is inside the solenoid. On the way out we would be decreasing the magnetic field and the solenoid will react by opposing that change or increasing the magnetic field. So we should see an increase in the current due to the effect of the solenoid on the way out.

The bottom line on induction is that the solenoid always sets up a current that opposes the change of the magnetic field inside it. So if you try to make it stronger by inserting a piece of iron – it produces a current that fights back. As you try to push the iron in you would feel a force pushing against you. Then on the way out if you try to make it weaker, the inductor reacts by making itself stronger (reinforcing the existing current from the battery). You would feel it pulling on the iron against your efforts to pull the iron away.

Induction, I think, is the hardest conceptual topic in O’Level physics. I have some electromagnets that I use with the class so they can literally get the feel of what happens.

[jetstar]

Thank you so much, Dr Daniel! You are totally awesome! My son understood your explanation perfectly

[notredame]

How many times are upper secondary pupils tested for the O level SPA? I heard that it is twice for some SPA components? Some schools send their Sec 3 pupils for the O level SPA this November while other schools do not. Does it mean that those which do not will have their pupils sit for the SPA twice next year? The average marks will be included in the respective subject of the O level exam?

Any information will be appreciated. Thank you.

[jewelbox]

Hi, appreciate help on the following sec 1 question. Thanks


A car is moving a constant velocity along a straight road. the engine provides a forward thrust of T. The opposition drag due to the wind is W and the frictional force from the ground is F.

a) What is the diffce betw speed and velocity?
b) Determine the resultant force on the car. Hence, explain why the car is moving at a constant velocity.
c) At the speed of 80km/h, the total opposing force on the car is 200N. what is the thrust of the engine?

d) To beat a traffic light, the driver decided to increase the thrust of the engine to 250N. The total opposing forces is then increased by 10N.
i) Give a possible reason for the increase in the total opposing forces when the thrust of the engine is increased.
ii) Calculate the resultant force on the car.
iii) The mass of the car is known to be 1,100kg. Using Newton's second law of Motion, calculate the acceleration of the car.

[Dr.033430Daniel]

jewelbox:

Hi, appreciate help on the following sec 1 question. Thanks

A car is moving a constant velocity along a straight road. the engine provides a forward thrust of T. The opposition drag due to the wind is W and the frictional force from the ground is F.

a) What is the difference between speed and velocity?

Speed is a scalar quantity and has only magnitude. Velocity is a vector quantity and has both magnitude and direction.

b) Determine the resultant force on the car. Hence, explain why the car is moving at a constant velocity.

The Resultant force = T-W-F = 0
If a car is moving at a constant velocity then there must be no resultant force. If there was any resultant force, there would be an acceleration.

c) At the speed of 80km/h, the total opposing force on the car is 200N. What is the thrust of the engine?

The thrust will also be 200N.

d) To beat a traffic light, the driver decided to increase the thrust of the engine to 250N. The total opposing forces is then increased by 10N.
i) Give a possible reason for the increase in the total opposing forces when the thrust of the engine is increased.

At a faster speed the force of air friction will be greater.

ii) Calculate the resultant force on the car.

250N – 210N = 40N

iii) The mass of the car is known to be 1,100kg. Using Newton's second law of Motion, calculate the acceleration of the car.

F = ma
40N = (1,100kg)a
a = 0.036 m/s2