Physics: Post your doubts here!

[VelaneDeBeaute]

19) what does translation mean here?To move a molecule, lets say, from one place to the other, without altering its shape! The same translation you might have studied in O Level Maths.
18) Why didnt we solve the formula by W.d= F * D. Did we not know the component of the force because the angle was not given or what? You can figure out the angle if you're trying to do it this way. You have the hypotenuse, and the perpendicular so use the trigonometric(sin) ratio.
16) Why is D not correct. The potential energy does not increase uniformly because the height does not increase uniformly. The ball may travel 1 m in its first second, 0.5 m in its second sec and so on. And what is P.E. equal to? mgh, right? So when 'h' doesn't increase uniformly, how can the Potential energy do so?

 

[Era]

i have got some doubts! i hope someone would help me out!
i asked my teacher that why do we NEED ac current in transformers! She said AC is must because current in ac changes direction so thus it will change the magnetic fiield! but my question is that WHY do we need to change the magnetic field?
and why the coil should be insulated?

 

[Era]

what helps transformers change its voltage?

 

[hassankhan]

hey guys plz can anyone help me with how to study physics i m not getting it at all....

 

[MysteRyGiRl]

hey guys plz can anyone help me with how to study physics i m not getting it at all....

AS?

 

[raamish]

S08:http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_s08_qp_1.pdf
DOnt understand these questions 6,16,21,39

 

[hassankhan]

AS?

Yes

 

[speedy20]

Can somebody give me a link for the physics application booklet *notes* as this section of physics is quite hard

 

[alcoholic 111]

Oct/Nov 2010 P41
Question 1 anyone ?

 

[memorypriest]

S08:http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s08_qp_1.pdf
DOnt understand these questions 6,16,21,39

Q6) Uniform circular motion
The acceleration acts perpendicularly to the direction of travel

Q16) A
Potential energy decrease.
There is no work done from bringing the positive charge vertically.

Q21) A
Deviation of hydrostatic pressure
P = F/A

Where Force is the weight of the liquid = mass x gravity = mg

Multiply h ( height ) for nominator and denominator
P = mgh / ah

Since ah is Area x Height, ah will be = to Volume

P = mgh / v

Furthermore, mass/volume = density
P = ρgh

Q39) C
Uranium mass is 235u where u = 1.66 x 10-27

 

[Mattman]

i have got some doubts! i hope someone would help me out!
i asked my teacher that why do we NEED ac current in transformers! She said AC is must because current in ac changes direction so thus it will change the magnetic fiield! but my question is that WHY do we need to change the magnetic field?
and why the coil should be insulated?

change in current=change in flux linkage. you need this to induce voltage in the core, so that the secondary current recieves the voltage/current as well.

 

[geek101]

S08:http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s08_qp_1.pdf


DOnt understand these questions 6,16,21,39

6) the object here is acceleration perpendicular to its motion...this means that the motion is caused by another speed in a direction perpendicular to the acc. >> parabolic pathway is followed by the ball. And direction then, will be changing through out the motion. And the speed will be constant as usual when an object follows a parabolic pathway.

21) pressure = density x g x h

Pressure = force / area , and because volume = area x height >> area = v / h
therefore P = force / v/h = F h / v , make v the subect of the formula >> v = Fh / p
now substitute the formula you got for v, in density = m /v >> density = m P / F h = m P / m g h
the ms get cancelled and you get density = p / gh >> p = density x g x h

39) from the data given in the beginning of the paper...
rest mass of proton = 1.67 x 10^-27
rest mass of an electron = 9.11 x 10^-31
in uranium the number of protons is 92 so do, 92 x 1.67 x 10^-27 = 1.5 x 10^-25 x 2 (for electrons) = 3 x 10^-25
the number of neutrons can vary but lets say its 143 >> 143 x 1.67 x 10^-27 = 2.4 x 10^-25
see so the numbers are in the range 10^-25, though this only requires assumption...

 

[Taci12]

hey guys plz can anyone help me with how to study physics i m not getting it at all....

Are there any specific chapters you have problems with?

Revise all chapters thoroughly, and practice a lot of past papers. If you don't understand any concept, clear all doubts before you go for the exam. All the best!

 

[InnocentAngel]

Why is the mean voltage = 0 in a sinusoidal curve for alternating current ?

 

[A*(a*)]

Can someone please post the answers to topical MCQs posted in a thread of AS level (Compiled by shakya or whatever his name was). And please upload kinematics MCQs answers, if it takes alot of time to upload all of them.

 

[Mattman]

Why is the mean voltage = 0 in a sinusoidal curve for alternating current ?

peak voltages=+5 and -5

5+(-5) divide by 2 and its 0.

 

[InnocentAngel]

peak voltages=+5 and -5

5+(-5) divide by 2 and its 0.

Oh lol so easy ! Stupid me ! Thanks buddy .

 

[InnocentAngel]

Please friends help me with this tricky and confusing question :

A surface is eradiated with lights of wavelength 5.5 x 10^-7m and electrons are just able to escape from the surface. When light of wavelength 5.0 x 10^-7m is used , elctrons emerge with energies of upto 3.6 x 10^-20 J. Obtain a value for the Planck constant .
Thanks in advance.

 

[memorypriest]

Please friends help me with this tricky and confusing question :

A surface is eradiated with lights of wavelength 5.5 x 10^-7m and electrons are just able to escape from the surface. When light of wavelength 5.0 x 10^-7m is used , elctrons emerge with energies of upto 3.6 x 10^-20 J. Obtain a value for the Planck constant .
Thanks in advance.

Energy of photon = work function of a metal + Maximum kinetic energy of the electron
E = Φ + K.E
hc/λ = Φ + K.E

Where c is the speed of light ( 3 x 10^8 m/s)

---------------------------------------------------
A surface is eradiated with lights of wavelength 5.5 x 10^-7m and electrons are just able to escape from the surface.

We can deduce that, just able to escape means K.E = 0
hc/λ = Φ + K.E
hc/5.5 x 10^-7 = Φ + 0 ------- (1)

When light of wavelength 5.0 x 10^-7m is used , electrons emerge with energies of up to 3.6 x 10^-20 J.
hc/λ = Φ + K.E
hc/5.0 x 10^-7 = Φ + 3.6 x 10^-20 ---------- (2)

(1) - (2)
hc/5.5 x 10^-7 - hc/5.0 x 10^-7 = - 3.6 x 10^-20
.
.
.
Solving... h = 6.6 x 10-34

 

[Naomiyxwnaoko]

I am having some problems answering summer 2008 paper 2 question (4c) . How do I get the the error?