ALL PHYSICS DOUBTS - POST HERE !!

[Malak]

if thats the case, then just keep in mind that

• if ray is going from denser to rarer, then angle of refraction will be greater than angle of incidence
• if ray is going from a rarer to a denser medium, then the angle of incidence is greater than the angle of refraction

Ohkey...Thx
And thx snake..

And Can anyone Explain me The motor effect...I cant seem to understand it :S
And wats the difference between An AC generator and a DC motor... :S
Thx

[Baladya]

An ac generator generates electricity by the electromagnetic induction. So basically u have only a magnet, wire, and an ammeter. Cut the field lines with the wire and u will see electricity being generated (the ammeter have a reading). On the other hand, a d.c motor works by electricity not make it. Again u have a magnet,coil around like a piece of wood or smth, split ring and brushes to allow it it to spin freely, and a POWER SUPPLY. This is the main diff, the power supply supllies the wire with electricity, when there is eletricity inside a wire, it creates a magnetic field. This magnetic fields interacts with the magnetic field of the magnet and causes the piece of wood to spin. The spinning motion cause other things to spin (for example wheals in toy cars). Also this is by d.c like the name say, while the a.c generator generates an a.c current Hope this helps

The motor effect i think is the thing i just told u about: when a wire has current in it, it creats a magnetic field. This magnetic field interacts with the magnet so it spins (just like u put to similar poles next to each other, they will repel and spin or smth) (this is why my dad keeps telling me not to leave electricity next to me while sleeping cuz its not healthy )[but m not sure of the health thing tho, cuz our teacher said that magnetic forces are okay to the body, but anyway this is just an extra thing ^^]

Now my turn
http://www.freeexampapers.us/IGCSE/Physics/CIE/2008%20Nov/0625_w08_qp_6.pdf

Question 2. I don't want answers, i just want to understand. First, what is the motion of the current? Second, if it comes from right to left, how come the table show that ciruit 3 has the least Voltage in the Voltmeter. To me it looks like it had a longer path through wire D>C>B and then S, so its supposed to lose more voltage and the voltage difference would be more...


http://www.freeexampapers.us/IGCSE/Physics/CIE/2008%20Nov/0625_w08_qp_03.pdf
http://www.freeexampapers.us/IGCSE/Physics/CIE/2008%20Nov/0625_w08_ms_3.pdf

Also this, Question 1) d) ii) I freakin don't understand why is 0.72 wrong!! I got the speed in (i) which is 0.6 and all i have to do is multiply by 1.2. This is what the mark scheme says but they say that the answer shouldnt be 0.72 HOWWWWW??!!!

[Baladya]

Hey is this right>>>>>?

The whole of a sealed, empty, dusty room is kept at a constant temperature of 15 °C. Light
shines into the room through a small outside window.
An observer points a TV camera with a magnifying lens into the room through a second
small window, set in an inside wall at right angles to the outside wall.
Dust particles in the room show up on the TV monitor screen as tiny specks of light.
(a) In the space below draw a diagram to show the motion of one of the specks of light over
a short period of time.

[Malak]

Thx alot....

Question:
What is the way of making sure that when u remove electrodes from a beaker the gap between the electrodes remain same?Or anyother way of measuring the gap between the electrodes while they are immersed :S

And can anyone clearly explain what is the Parallax error and how to avoid it?

Thx...

[Helium]

When calculating the gradient of a line in PAPER 6 a mark is given for drawing a triangle 'more than half the length of the line'.

The examiners report also  refers to the TRIANGLE METHOD alot. What is this method/how does it work.

The only way I know to calc. a gradient is using (y2-y1)/(x2-x1). 

Well there are 2 ways to calculate the gradient.

1. By taking 2 points on the line and using (y2-y1)/(x2-x1) like you said.

2. Is by using the triangle method you take the 2 points you connect them by a tringle ,  By forming a traingle you calculate the differece
in y and divide by difference in x. The direction of the line will tell if the value will be positive or negative.

hope u understsand,
use this link
http://www.mathsteacher.com.au/year10/ch03_linear_graphs/02_gradient/line.htm



Its quite simple if you get used to it, and its much quicker than using th formula.

[Ghost Of Highbury]

An ac generator generates electricity by the electromagnetic induction. So basically u have only a magnet, wire, and an ammeter. Cut the field lines with the wire and u will see electricity being generated (the ammeter have a reading). On the other hand, a d.c motor works by electricity not make it. Again u have a magnet,coil around like a piece of wood or smth, split ring and brushes to allow it it to spin freely, and a POWER SUPPLY. This is the main diff, the power supply supllies the wire with electricity, when there is eletricity inside a wire, it creates a magnetic field. This magnetic fields interacts with the magnetic field of the magnet and causes the piece of wood to spin. The spinning motion cause other things to spin (for example wheals in toy cars). Also this is by d.c like the name say, while the a.c generator generates an a.c current Hope this helps

The motor effect i think is the thing i just told u about: when a wire has current in it, it creats a magnetic field. This magnetic field interacts with the magnet so it spins (just like u put to similar poles next to each other, they will repel and spin or smth) (this is why my dad keeps telling me not to leave electricity next to me while sleeping cuz its not healthy )[but m not sure of the health thing tho, cuz our teacher said that magnetic forces are okay to the body, but anyway this is just an extra thing ^^]

Now my turn
http://www.freeexampapers.us/IGCSE/Physics/CIE/2008%20Nov/0625_w08_qp_6.pdf

Question 2. I don't want answers, i just want to understand. First, what is the motion of the current? Second, if it comes from right to left, how come the table show that ciruit 3 has the least Voltage in the Voltmeter. To me it looks like it had a longer path through wire D>C>B and then S, so its supposed to lose more voltage and the voltage difference would be more...


http://www.freeexampapers.us/IGCSE/Physics/CIE/2008%20Nov/0625_w08_qp_03.pdf
http://www.freeexampapers.us/IGCSE/Physics/CIE/2008%20Nov/0625_w08_ms_3.pdf

Also this, Question 1) d) ii) I freakin don't understand why is 0.72 wrong!! I got the speed in (i) which is 0.6 and all i have to do is multiply by 1.2. This is what the mark scheme says but they say that the answer shouldnt be 0.72 HOWWWWW??!!!

Im myself confused about the circuit thing, sry can't help in that.

However the other one.

U cannot use the formula speed - distance/time for an object which is accelerating

Use the formula s = 0.5at²

s = 0.5*0.5*1.2² = 0.25 * 1.2 * 1.2 = 0.36m

and about the dust particle, yes its correct, but just make a dot for a particle. Something like the attached one.

[Ghost Of Highbury]

Thx alot....

Question:
What is the way of making sure that when u remove electrodes from a beaker the gap between the electrodes remain same?Or anyother way of measuring the gap between the electrodes while they are immersed :S

And can anyone clearly explain what is the Parallax error and how to avoid it?

Thx...

No clue about the electrodes thing. it was left unanswered here too : https://studentforums.biz/index.php/topic,1057.msg8998.html#msg8998

Parallax Error : Error in reading an instrument employing a scale and pointer because the observer's eye and pointer are not in a line perpendicular to the plane of the scale.

Avoid parallax error : Placing the eye perpendicular to the marking on the scale to be read. If you are measuring the volume of liquid in a measuring cylinder , make sure you positioned your eye to take readings at the bottom of menicus for water and top of menicus for mercury.

[Baladya]

Im myself confused about the circuit thing, sry can't help in that.

However the other one.

U cannot use the formula speed - distance/time for an object which is accelerating

Use the formula s = 0.5at²

s = 0.5*0.5*1.2² = 0.25 * 1.2 * 1.2 = 0.36m

and about the dust particle, yes its correct, but just make a dot for a particle. Something like the attached one.

WOW. 5 days for the exam and i still don't know this rule... Thanks school  And Thanks Aodi  

[Ghost Of Highbury]

WOW. 5 days for the exam and i still don't know this rule... Thanks school  And Thanks Aodi  

Your Welcome.

[Snake]

I thought the formula to find acceleration was A=V-U/T
With V being Final speed and U initial speed and T time

[Saladin]

I thought the formula to find acceleration was A=V-U/T
With V being Final speed and U initial speed and T time

That is correct.

[Malak]

No clue about the electrodes thing. it was left unanswered here too : https://studentforums.biz/index.php/topic,1057.msg8998.html#msg8998

Parallax Error : Error in reading an instrument employing a scale and pointer because the observer's eye and pointer are not in a line perpendicular to the plane of the scale.

Avoid parallax error : Placing the eye perpendicular to the marking on the scale to be read. If you are measuring the volume of liquid in a measuring cylinder , make sure you positioned your eye to take readings at the bottom of menicus for water and top of menicus for mercury.

Thx alot

Another question :

When u wrap the string aroung something and measure that length...How do u find the circumference...
Do you multiply the length by the number of times the string is wrapped or u divide it by that number?

[Hesham Mhd]

Can any1 plz explain the thermal expansion? And What expands more.. solids, liquids or gases and why? Thanks in advance

[Hesham Mhd]

Another One :
If a ray diagram is given, what should be done? i mean, when should we magnify and when should we simply draw the upside-down image? Thanks

[Ghost Of Highbury]

@ang3l - if u wrap the string 5 times around the object. the circumfrence = string length/5