Biology; Chemistry; Physics: Post your doubts here!

[TheStallion-Reborn]

I'd really appreciate some help in Bio regarding teeth ( mainly cross section and internal structure) and the nitrogen cycle...Ive always been confused cuz theres so many different bacteria involved....and how nitrates are being formed but CO2 is still being produced. Any help or even any notes would be rly appreciated guys!! Exams pretty closeee... Thanks.

I can guide u about nitrogen cycle, but m not so sure about teeth myself. so tag me in any post u find helpful abou teeth. Let's start from th air present in the soil. The plants need nitrate ions. And they get these from the nitrogen present in the air inside the soil. The leguminous (bean) plants have bacteria in their roots, known as nitrogen fixing bacteria which turn nitrogen in the air into nitrate ions. the plants make proteins from these nitrate ions. the herbivorous feed on these plants and take up nitrogen molecules or carnivorous feed on the herbivorous to attain these nitrogen molecules. When any of these organisms die, another kind of bacteria break down these nitrate ions into nitrogen gas during decomposition in a process known as denitrification. i hope that helps.

 

[TheStallion-Reborn]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s12_qp_22.pdf question 8 part a sub part 1, i am not really getting the marking schemehttp://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s12_ms_22.pdf. how many marks will I get?

 

[Saad Mughal]

View attachment 24216 http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s12_qp_22.pdf question 8 part a sub part 1, i am not really getting the marking schemehttp://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s12_ms_22.pdf. how many marks will I get?

1 mark for the symbols.
1 mark for ammeter in series.
But, no W is labelled, -0.5 mark.
Voltmeter is connected in series, it should be connected across the wire.
1.5/3 is what you would get.

 

[asma tareen]

YOU CAN CHECK FOR TEETH AND NITROGEN CYCLES HERE!!! AhsanS
http://www.e-socrates.org/course/view.php?id=127

 

[TheStallion-Reborn]

firstly nope. If it had been parallel, your answer is right


K now lets start from beginning. A lamp is supposed to be more bright when its resistance is high, this being because as the resistance of the lamp is high, the potential difference across it would be higher. this would mean that more energy would be required per charge when going through the lamp, and as a result more heat and thus light energy will be produced, resulting in a brighter lamp. NOW THIS IS WRONG

Why? because due to the high resistance of the bulb, the overall current in the circuit would decrease. As a result, the p.d across the lamp would decrease too. What really happens is that the lamp glows brighter when its resistance is low. You might question this as higher resistance means more heat, and i am saying the exact opposite.

Well this is because due to the low resistance, the overall current in the circuit increases. Now you might think that the p.d across the lamp might be lower too due to the lower resistance but this is not so. Because of the higher current, more electrons would be trying to go through the same narrow path of the wire through the lamp. This would result in a high p.d across the lamp, and overall a brighter lamp

Hskk asma tareen

applies to both series a nd parallel. right?

 

[TheStallion-Reborn]

Well this is because due to the low resistance, the overall current in the circuit increases. Now you might think that the p.d across the lamp might be lower too due to the lower resistance but this is not so. Because of the higher current, more electrons would be trying to go through the same narrow path of the wire through the lamp. This would result in a high p.d across the lamp, and overall a brighter lamp

dude, R=V/I so when resistance decreases, the pd is bound to decrease. aint it??

 

[fatima0000]

(f) recognise and use the conventions and symbols contained in ‘Signs, Symbols and Systematics’,
Association for Science Education, 2000.
this is point i read in physics syllabus . i wanna know that what does it mean??? help requiredd

 

[TheStallion-Reborn]

(f) recognise and use the conventions and symbols contained in ‘Signs, Symbols and Systematics’,
Association for Science Education, 2000.
this is point i read in physics syllabus . i wanna know that what does it mean??? help requiredd

i guess its about symbols of electrical components

 

[fatima0000]

i guess its about symbols of electrical components

but i dont think so because it is from the topic Physical Quantities, Units and Measurement

 

[TheStallion-Reborn]

alright so this is a parallel circuit and we al know that the pd is equal everywhere. now i have two question:
1) what if the resistors have different resistances, will the pd across them still be equal, if not what is it gona be?
2) if all the resistors have the same resistance, will al of them have the same pd or only resistor 2&3 will have the same pd?

 

[asma tareen]

Well for the first one p.d. Will remain same but the current in both the resistors would be different
Secondly if all the resistors are having the same resistance then we can se that the overall circuit is in series the pd of 1 would be different from 2 nd 3
That what I think

 

[fatima0000]

what is the effect of friction on motion of vehicle in context with road condition, tyre surface, braking force, braking distance, thinking distance and stopping distance.

 

[papajohn]

Please anyone know this, Your effort will be appreciated

 

[usama321]

dude, R=V/I so when resistance decreases, the pd is bound to decrease. aint it??

but the current would decrease too, resulting in the p.d across the lamp decreasing too.

 

[fatima0000]

Please anyone know this, Your effort will be appreciated

d) mr of AgI = 108 +127
= 235
mole = mss / mr
=4.7/235
=0.02 mol

(e) 1 : 1
0.02 : x
x = 0.02mol

 

[papajohn]

d) mr of AgI = 108 +127
= 235
mole = mss / mr
=4.7/235
=0.02 mol

(e) 1 : 1
0.02 : x
x = 0.02mol

These are absolutely correct. but i m stuck on "F". How do we calculate the concentration of Silver nitrate?

 

[usama321]

what is the effect of friction on motion of vehicle in context with road condition, tyre surface, braking force, braking distance, thinking distance and stopping distance.

Road condition: If the road is wet, friction would be less between the road and the tyres as the surface is slippery. If it is dry, there would be more friction.

Tyre surface: If the surface of the tyres is smooth, there would be less friction. this usually happens if the tyres are old. If there are treads or tracks in the tyres there would be more friction. Similarly to the road, if they are wet, there would be less frction.

Breaking force: If the breaking force is more, than there should be more friction in the tyres and brakes.

Braking distance: Braking distance is the distance covered by the car while the brakes are being applied. Don't know what to write in this one. maybe if the breaking distance is more, than the friction is lesser compared to a shorter braking distance?

Thinking distance: It is the distance covered by the body, during which the driver decides to apply the brake. Don't know what it has to do with friction

Stopping distance: ?

Well in all the above, where there is more friction the vehicle would of course stop faster, and if there is less friction, it would be the opposite. E-g a wet road could cause an accident, similarly old and worn out tyres can cause an accident too etc

 

[usama321]

These are absolutely correct. but i m stuck on "F". How do we calculate the concentration of Silver nitrate?

did you calculate the volume in part a? If so, concentration = number of moles *1000/volume (this equation is applicable only if the volume is in cm^3, if it is already dm^3, don;t multiply with 1000)

 

[papajohn]

did you calculate the volume in part a? If so, concentration = number of moles *1000/volume (this equation is applicable only if the volume is in cm^3, if it is already dm^3, don;t multiply with 1000)

Thanks dude now get it.The volume is given in part a..

 

[usama321]

Thanks dude now get it.The volume is given in part a..