Biology; Chemistry; Physics: Post your doubts here!

[RAMEEZA]

answer plz..
Is it possible for an electric field to exist in a vacum and why?

 

[cool.fireboy24]

How to find out percentage purity of a substance

 

[Uzair umar]

we can jus

answer plz..
Is it possible for an electric field to exist in a vacum and why?

t simply say it as if electricity can flow through vaccum... so electron can flow too...
but in some cases u have to provide a potential difference too...

 

[Fari Inayat]

assume y as x
CxHx+33+24+33=132
12x+x+90=132
x=3.23=3
Cx=12x3=36
36+y+90=132
soy=6
check
HO2CCxHyCO2H
1+16x2+12+12x3+1x6+12+16x2+1=132

From where 132 came I did'nt get it?

 

[Rockytigress]

Can anybody give me past papers of physics (1990-2000).... ASAP..... its URGENT

 

[abdur_rafay]

Does anybody have a chemistry Olevel 2016 past papers???

 

[phanthuan108]

You can help me download this book?
Cambridge IGCSE Chemistry Coursebook
by Richard Harwood; Ian Lodge
(http://www.ebooks.com/1019240/cambridge-igcse-chemistry-coursebook/harwood-richard-lodge-ian/)

Let you send me link download or file, link to my Email: [email protected]
Thanks so so much!

 

[RAMEEZA]

do anyone have this book
Longman 1001 Physics MCQs for O Level
By Tan Peng Yeon
If so..... i want the mcqs for the topic current electricity

 

[AquaRoxas]

In endothermic reactions, is the enthalpy of bond breaking greater than the enthalpy of bond forming or vice versa? Thanks.

 

[RAMEEZA]

hey! Can anyone plz explain logic gates...i mean all that NOR...AND...NAND etc
kinda difficult i think so?

 

[A*****]

Can anybody plz help me with these questions...
1) Explain why widely different values of resistors are needed in different types of circuits.
2) Discuss the need to choose components with suitable power ratings.
3) Explain the use of thermistors and light dependent resistors as input sensors.

 

[Talha Jameel]

Can anybody plz help me with these questions...
1) Explain why widely different values of resistors are needed in different types of circuits.
2) Discuss the need to choose components with suitable power ratings.
3) Explain the use of thermistors and light dependent resistors as input sensors.

1. Resistors are used to control the flow of current. A circuit might require different values of current to pass through it, so in order to meet the circuit's requirement, different values of resistors are available.

2. While dealing with circuits one should take special care about the power rating of the components used.
Power rating means the amount of current and voltage a component can handle becasue is given by Power = voltage x times (unit of power is watts)
For example, if you are using a small bulb of 6 watts and plugging it with 220 v mains. What would happen? Obviously it would blow up.
Also the opposite example would be; if we connect a 45 watts energy saver with a cell of 1.5 v then the bulb won't work at all.
So we always need to be vigilant about the power rating of the components used in a particular circuit.
We also need to be vigilant about the fluctuations of current and voltage, therefore, a component must be chosen with some tolerance.

3. Resistance of thermistor decreases when temperature increases & vice versa.
It can be used in a fire alarm; When the surrounding gets too hot (Possibly due to fire), resistance of Thermistor will decrease and a large amount of current will pass through the circuit, activating the alarm.

While, resistance of LDR is dependent upon light i.e when light falls on the LDR its resistance decreases & vice versa.
LDR can be used in burglar alarm systems. Think of a shop which closes at night. When someone breaks into the shop and switches on the light or uses a flashlight (which will fall on the LDR) resistance will drop, allowing current to flow through the circuit and activating the alarm.

I hope it helped.

 

[A*****]

hey! Can anyone plz explain logic gates...i mean all that NOR...AND...NAND etc
kinda difficult i think so?

No they aren't that much difficult to understand...
See, we are concerned with 5 of them, namely NOT, AND, NAND, OR, NOR.
1) NOT: Its simply an inverter...means that it reverses the input..
So, its truth table is:
A Output
0 1
1 0
2)AND: In this logic gate, the output will only be positive if both input A 'AND' B are positive...otherwise it would be zero. Therefore its truth table will be:
A B Output
0 0 0
0 1 0
1 0 0
1 1 1
3)NAND: It is the reverse of AND gate...in other words it is basically a NOT AND gate. So, the output will be positive if both input A 'AND' B are 'NOT' positive. Its truth table is:
A B Output
0 0 1
0 1 1
1 0 1
1 1 0
4)OR: In this logic gate, the output will be positive if either input A 'OR' B is positive, so its truth table will be:
A B Output
0 0 0
0 1 1
1 0 1
1 1 1
5)NOR: Just like the NAND gate was the reverse of the AND gate, the NOR gate is the reverse of the OR gate. Its output will be positive if neither input A 'NOR' B is positive. Consequently its truth table will be:
A B Output
0 0 1
0 1 0
1 0 0
1 1 0
Hope it was helpful...

 

[A*****]

1. Resistors are used to control the flow of current. A circuit might require different values of current to pass through it, so in order to meet the circuit's requirement, different values of resistors are available.

2. While dealing with circuits one should take special care about the power rating of the components used.
Power rating means the amount of current and voltage a component can handle becasue is given by Power = voltage x times (unit of power is watts)
For example, if you are using a small bulb of 6 watts and plugging it with 220 v mains. What would happen? Obviously it would blow up.
Also the opposite example would be; if we connect a 45 watts energy saver with a cell of 1.5 v then the bulb won't work at all.
So we always need to be vigilant about the power rating of the components used in a particular circuit.
We also need to be vigilant about the fluctuations of current and voltage, therefore, a component must be chosen with some tolerance.

3. Resistance of thermistor decreases when temperature increases & vice versa.
It can be used in a fire alarm; When the surrounding gets too hot (Possibly due to fire), resistance of Thermistor will decrease and a large amount of current will pass through the circuit, activating the alarm.

While, resistance of LDR is dependent upon light i.e when light falls on the LDR its resistance decreases & vice versa.
LDR can be used in burglar alarm systems. Think of a shop which closes at night. When someone breaks into the shop and switches on the light or uses a flashlight (which will fall on the LDR) resistance will drop, allowing current to flow through the circuit and activating the alarm.

I hope it helped.

Thanx alottt...

 

[taughtware]

2. While dealing with circuits one should take special care about the power rating of the components used.
Power rating means the amount of current and voltage a component can handle becasue is given by Power = voltage x times (unit of power is watts)
For example, if you are using a small bulb of 6 watts and plugging it with 220 v mains. What would happen? Obviously it would blow up.
Also the opposite example would be; if we connect a 45 watts energy saver with a cell of 1.5 v then the bulb won't work at all.
So we always need to be vigilant about the power rating of the components used in a particular circuit.
We also need to be vigilant about the fluctuations of current and voltage, therefore, a component must be chosen with some tolerance.

I think you meant P = I V instead of "Power = voltage x times".

Simply put, power rating of a resistor is the maximum amount of electrical energy per second (J/s or W) that the resistor can convert into heat without getting damaged.

Usually power rating depends on the size of the resistor.

While discussing power ratings of resistors, it may be useful to say that using resistors with large power ratings means that they will occupy more space on the circuit board and using resistors with lower (just enough) power ratings means that they may become damaged easily due to small fluctuations (That is why a margin is kept when choosing a resistor with a suitable power rating).

 

[Talha Jameel]

I think you meant P = I V instead of "Power = voltage x times".

Simply put, power rating of a resistor is the maximum amount of electrical energy per second (J/s or W) that the resistor can convert into heat without getting damaged.

Usually power rating depends on the size of the resistor.

While discussing power ratings of resistors, it may be useful to say that using resistors with large power ratings means that they will occupy more space on the circuit board and using resistors with lower (just enough) power ratings means that they may become damaged easily due to small fluctuations (That is why a margin is kept when choosing a resistor with a suitable power rating).

Yeah, My bad.

 

[Ayesha Asif333]

No they aren't that much difficult to understand...
See, we are concerned with 5 of them, namely NOT, AND, NAND, OR, NOR.
1) NOT: Its simply an inverter...means that it reverses the input..
So, its truth table is:
A Output
0 1 UI
1 0
2)AND: In this logic gate, the output will only be positive if both input A 'AND' B are positive...otherwise it would be zero. Therefore its truth table will be:
A B Output
0 0 0
0 1 0
1 0 0
1 1 1
3)NAND: It is the reverse of AND gate...in other words it is basically a NOT AND gate. So, the output will be positive if both input A 'AND' B are 'NOT' positive. Its truth table is:
A B Output
0 0 1
0 1 1
1 0 1
1 1 0
4)OR: In this logic gate, the output will be positive if either input A 'OR' B is positive, so its truth table will be:
A B Output
0 0 0
0 1 1
1 0 1
1 1 1
5)NOR: Just like the NAND gate was the reverse of the AND gate, the NOR gate is the reverse of the OR gate. Its output will be positive if neither input A 'NOR' B is positive. Consequently its truth table will be:
A B Output
0 0 1
0 1 0
1 0 0
1 1 0
Hope it was helpful...

1. Resistors are used to control the flow of current. A circuit might require different values of current to pass through it, so in order to meet the circuit's requirement, different values of resistors are available.

2. While dealing with circuits one should take special care about the power rating of the components used.
Power rating means the amount of current and voltage a component can handle becasue is given by Power = voltage x times (unit of power is watts)
For example, if you are using a small bulb of 6 watts and plugging it with 220 v mains. What would happen? Obviously it would blow up.
Also the opposite example would be; if we connect a 45 watts energy saver with a cell of 1.5 v then the bulb won't work at all.
So we always need to be vigilant about the power rating of the components used in a particular circuit.
We also need to be vigilant about the fluctuations of current and voltage, therefore, a component must be chosen with some tolerance.

3. Resistance of thermistor decreases when temperature increases & vice versa.
It can be used in a fire alarm; When the surrounding gets too hot (Possibly due to fire), resistance of Thermistor will decrease and a large amount of current will pass through the circuit, activating the alarm.

While, resistance of LDR is dependent upon light i.e when light falls on the LDR its resistance decreases & vice versa.
LDR can be used in burglar alarm systems. Think of a shop which closes at night. When someone breaks into the shop and switches on the light or uses a flashlight (which will fall on the LDR) resistance will drop, allowing current to flow through the circuit and activating the alarm.

I hope it helped.

I think you meant P = I V instead of "Power = voltage x times".

Simply put, power rating of a resistor is the maximum amount of electrical energy per second (J/s or W) that the resistor can convert into heat without getting damaged.

Usually power rating depends on the size of the resistor.

While discussing power ratings of resistors, it may be useful to say that using resistors with large power ratings means that they will occupy more space on the circuit board and using resistors with lower (just enough) power ratings means that they may become damaged easily due to small fluctuations (That is why a margin is kept when choosing a resistor with a suitable power rating).

MA! Such intelligent people y'all , may Allah increase your knowledge and you keep sharing it. Best of luck

 

[A*****]

MA! Such intelligent people y'all , may Allah increase your knowledge and you keep sharing it. Best of luck

Ohh Thanx

 

[XxbeliebersrockXx]

Hey there!
it's a good idea to create a thread like this as it's gonna help some students like me ... btw i have some problems while doing physics ATP paper...
can u give me some specific tips on how to ace this ATP as i'm to appear for CIEs this year... this is really urgent... any notes or important questions will be of great help for me ....
i will be waiting for useful tips and notes

 

[Talha Jameel]

Hey there!
it's a good idea to create a thread like this as it's gonna help some students like me ... btw i have some problems while doing physics ATP paper...
can u give me some specific tips on how to ace this ATP as i'm to appear for CIEs this year... this is really urgent... any notes or important questions will be of great help for me ....
i will be waiting for useful tips and notes

The key to A* is solve as many past papers as possible from REDSPOT. Once you've done 7-8 papers, you'll be able to solve the paper within 20-30 mins.
I'm sending you the notes in Personal Message. Hope you find them of good use.