Physics, Chemistry and Biology: Post your doubts here!

[princess sofia]

cn smeone plz exlain me thx question

 

[Lavinge]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Physics (0625)/0625_s11_qp_33.pdf how do you do 3b?

 

[Xylferion]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Physics (0625)/0625_w13_qp_31.pdf
question 10b1 pleaseee

The amplitude of one wave is 1.5 V.

5 waves would be 1.5 * 5 which is 7.5 V.

 

[Xylferion]

cn smeone plz exlain me thx question View attachment 43124

If you had actually taken the time to read your syllabus, you'd have known by now that a diode aids in making current flow in only one direction.

So if you take alternating current, add a diode, you'll get direct current. This process is known as rectification. However you're only using 1 diode.

1 diode will give you half wave rectification, whereas 4 diodes will result in full wave rectification.

So in the diagram you only draw the top loops of each wave, leave the bottom parts dotted.

 

[DeadlYxDemon]

Can anyone post Defination for Pressure, Density? It came in May/June - 2013 paper!

 

[R_Ma7mooD]

If you had actually taken the time to read your syllabus, you'd have known by now that a diode aids in making current flow in only one direction.

So if you take alternating current, add a diode, you'll get direct current. This process is known as rectification. However you're only using 1 diode.

1 diode will give you half wave rectification, whereas 4 diodes will result in full wave rectification.

So in the diagram you only draw the top loops of each wave, leave the bottom parts dotted.

what if three diodes are used?

 

[princess sofia]

If you had actually taken the time to read your syllabus, you'd have known by now that a diode aids in making current flow in only one direction.

So if you take alternating current, add a diode, you'll get direct current. This process is known as rectification. However you're only using 1 diode.

1 diode will give you half wave rectification, whereas 4 diodes will result in full wave rectification.

So in the diagram you only draw the top loops of each wave, leave the bottom parts dotted.

thnx , jst wasnt sure abt it dats why asked

 

[R_Ma7mooD]

Can anyone post Defination for Pressure, Density? It came in May/June - 2013 paper!

Pressure is the amount of force acting per unit area at right angle of a surface.
Density is the ratio of mass to volume of a substance.

 

[princess sofia]

Can anyone post Defination for Pressure, Density? It came in May/June - 2013 paper!

pressure is defined as force acting per unit area [ write formula n S.I unit]
density is defined as mass per unit volume

 

[Xylferion]

http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Physics (0625)/0625_s11_qp_33.pdf how do you do 3b?

It weight of bar B acts directly below its centre of mass. So draw an arrow under the bar, where it says Iron bar B.

For the next part of the question it asks you to find the distance, d, to the centre of mass. The total length of the bar is 1.4 m. Half of this is 0.7 m.

The pivot is at 0.2 m of the bar. So the remaining distance from the the pivot to the centre of mass is 0.7 m - 0.2 m. You will get 0.5 m which is the distance, d.

Moment = Force * perpendicular distance

Force = 40 N
Perpendicular distance = 1.4 m - 0.2 m = 1.2 m. This is the distance from the pivot to the 40 N point.

40 * 1.2 = 48 Nm


Now for the next part, the total downward force applied by the slab.

Total clockwise moments = Total anti-clockwise moments ---> during equilibrium.

Force x 0.2 = 48 N
Force = 48 N / 0.2 = 240 N.

The force applied downwards by the slab is 240 N.

To reduce the force needed to lift the slab, simply move it closer to the slab. It's as simple as that. Try it your self. Place a scale on an eraser, and an object on top of the scale. Adjust the distance of the rubber from the object, and you'll see, the closer it is, the less force you need, to lift it.

 

[Xylferion]

what if three diodes are used?

That's not covered in the IGCSE syllabus, however if you really want to know, even though you need to, read up on it here: http://www.allaboutcircuits.com/vol_3/chpt_3/4.html

Edit:- CIE only wants you to be able to describe full wave and half wave rectification. All they want you to do is know how a diode can be used, and one of its uses is rectification of alternating current.

 

[Xylferion]

thnx , jst wasnt sure abt it dats why asked

If you have the time, I suggest quickly reading through the syllabus content!

Everything that CIE bases its questions of, is included there

 

[Gamedos]

Help how to do i and ii

 

[R_Ma7mooD]

That's not covered in the IGCSE syllabus, however if you really want to know, even though you need to, read up on it here: http://www.allaboutcircuits.com/vol_3/chpt_3/4.html

Edit:- CIE only wants you to be able to describe full wave and half wave rectification. All they want you to do is know how a diode can be used, and one of its uses is rectification of alternating current.

Oh okay. Thanx bro

I didn't understand question 9: can u help me with it?
http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Physics (0625)/0625_s11_qp_33.pdf

 

[princess sofia]

If you have the time, I suggest quickly reading through the syllabus content!

Everything that CIE bases its questions of, is included there

they have nt asked for such details of diodes , n none of igcse books have it in such detail , btw thnks 4 ur suggestion

 

[Faiza Anwar]

(ii) The gardener is told that, by painting the drum white, he can reduce the quantity of
radiation absorbed and so reduce the rate of evaporation.
Describe an experiment to show that black surfaces are better absorbers of
radiation than white surfaces. You may include a diagram.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
............................................................................................................................. [4]
[Total: 6]
cn we use crookes radiometer experiment in thx ? cze its nt mentioned in markscheme

make to drums,(label one white nd the other black) fill them with water, place a heater b/w them, then write "measure initial temp in both, switch on heater, after some time switch off heater measure temp of water, calculate temp change. water in black drum will show greater temp change.."

 

[princess sofia]

Oh okay. Thanx bro

I didn't understand question 9: can u help me with it?
http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Physics (0625)/0625_s11_qp_33.pdf

here they r askng concept of felmings left hand rule
for a (i) using flemings rule we find direction of force is downwards
(ii) force acts cze magnetic field around current carring wire and dat of magnet concide
(iii) as both are reversed so direction remains same , if we reverse one so thn the direction would change
for (b) again we ll be using flemings left hand rule bt remember for negative charge , the direction of current ll be takn opposite
(ii) the path ll be parabolic
cn any1 explain , why its parabolic ?

 

[princess sofia]

make to drums,(label one white nd the other black) fill them with water, place a heater b/w them, then write "measure initial temp in both, switch on heater, after some time switch off heater measure temp of water, calculate temp change. water in black drum will show greater temp change.."

i knw dat bt cn we use the crookes ratemeter exp for thx
Xylferion cn u ans ?

 

[R_Ma7mooD]

here they r askng concept of felmings left hand rule
for a (i) using flemings rule we find direction of force is downwards
(ii) force acts cze magnetic field around current carring wire and dat of magnet concide
(iii) as both are reversed so direction remains same , if we reverse one so thn the direction would change
for (b) again we ll be using flemings left hand rule bt remember for negative charge , the direction of current ll be takn opposite
(ii) the path ll be parabolic
cn any1 explain , why its parabolic ?

Thanks that clears up my conflicts.

 

[Xylferion]

Oh okay. Thanx bro

I didn't understand question 9: can u help me with it?
http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Physics (0625)/0625_s11_qp_33.pdf

First their asking you for the direction of the force, you have a current carrying conductor which is the wire. You automatically decide that this questions requires the use of Flemings left hand rule. Now the current is pointing towards you, so you point your central finger towards you, you will observe that your thumb finger points down.

Since your thumb finger is pointing down, we immediately know that the force is pointing downwards due to the fact that your thu"M"b = Motion(Force).

For the next part, you're asked to write why this force exists in the first place. The current carrying conductor ( wire ), contains charges. These charges are in the form of electrons. When charges enter a magnetic field, they will always experience a force. So your best answer for this would be, The charges in the wire experience a force as they pass through the magnetic field lines.

Flip your hand upside down because the current direction is reversed, you will see that your thumb now points up. So the direction of the force is acting upwards.

For b) i) the magnetic field is acting into the paper. So use the right hand rule, and you'll see that the magnetic field points downwards. Drawn an arrow at P pointing down.

ii) As the magnetic field is a curved path going downwards, the particle will also follow a curved path, because it is now in the magnetic field.