Physics: Post your doubts here!

[Heisenberg]

You cannot use the actual capacitance of X for the first part because you don't know the don't know the potential difference across X. So it is easier to use the effective capacitance and the total potential difference. Otherwise you can also do it by the longer method if you want to use the actual capacitance.
First calculate the potential difference cross X.
Total resistance in series is 12 micro farad and 24 micro farad from the parallel combination. So, potential across X=
(capacitance of X/ total capacitance in series) * 9
(1/12)/(1/12+1/24) * 9 = 6v
Now use Q =CV for X
Q = 12 micro farad * 6 =7.2* 10^-5 =72 micro C
You get the same answer, just a longer calculation.

For Y you can use the actual capacitance because you already know the potential difference cross Y from your previous calculations.

Sorry, but farad is resistance? I thought it was the capacitance. So you can use it to calculate p.d. just like actual resistance?

 

[snowbrood]

The Answer will be B that i think so,PLEASE do tell me if i am right?
A: In A weight is acting downward and the normal reaction force at the end of ladder is upward and the force P is the normal reaction force by the wall in straight direction.Which means the ladder is not sliding and on the equilibrium postion
B: In B weight is acting downward and the normal reaction force at the end of ladder is upward and the force P force P is acting slightly upward because the ladder is sliding .
C: In C weight is acting downward again and the normal reaction force at the end of ladder is now not acting against the direction of weight it is slighlt inward.
D : In D weight is acting downward again and the normal reaction force at the end of ladder is again not acting against the direction of weight it is slightly Outward
Thus the Answer will be B

look buddy this question need some focus the wall is rough but the floor is not
because of contact of ladder with both wall and floor there would be component of force perpendicular to the wall and the floor.
now since there is the floor has no friction so there would be no horizantal component and the result would be only vertical because of the contact force.
now the wall has both the frictional force and contact force. the resultant to vertical and horizantal force would be a hypotenuse

 

[Light Yagami]

Why is the answer D:-

 

[littlecloud11]

Sorry, but farad is resistance? I thought it was the capacitance. So you can use it to calculate p.d. just like actual resistance?

I am so sorry, i wrote resistance instead of capacitance.
I meant the capacitance in series is 12 and 24 micro farad.
And you can use capacitance to calculate potential difference by using the ratio of capacitance * total potential.

 

[Light Yagami]

Why is the answer C:-

 

[Dug]

Why is the answer C:-
View attachment 22151

Q = ne
Q = It

ne = It
n(1.6*10^-19) = (10)(1)
n = 6.3*10^19

 

[Ahmedraza73]

Can any solve my question?
A taut wire is clamped at two points 1.0m apart.It is plucked near one end.which are three longest wavelengths on the vibrating wire?
A: 1.0m, 0.50m, 0.25m
B: 1.0m, 0.67m, 0.50m
C; 2.0m, 0.67m, 0.40m
D: 2.0m, 1.0m, 0 .50m
E: 2.0m, 1.0m, 0.67m

 

[Light Yagami]

Q = ne
Q = It

ne = It
n(1.6*10^-19) = (10)(1)
n = 6.3*10^19

Why did they give the cross section of the wire then?

 

[Ahmedraza73]

Why is the answer D:-
View attachment 22149

d sin theta= n lambda
d=1.0*10^-3/500=2*10^-6
sin 90=1
making n a subject of formula: n=d sin theta/lamda
n=2*10^-6*sin 90/600*10^-9=3.3
since n is an integar n=3
now observer is looking at three positons X Y Z
X=2 ORDER
Z=2 ORDER
Y=0 ORDER
SO n=2+2+3=7

 

[Arjun Dhanak]

Hi. I have a doubt in Photoelectric effect. I don't understand how the photoelectric current reduces when we reduce the wavelength.
Qs. 7C http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_s11_qp_41.pdf

 

[Omar99]

can u tell me how to study telecomunication in application

 

[Yousuf Ykr]

Can any solve my question?
A taut wire is clamped at two points 1.0m apart.It is plucked near one end.which are three longest wavelengths on the vibrating wire?
A: 1.0m, 0.50m, 0.25m
B: 1.0m, 0.67m, 0.50m
C; 2.0m, 0.67m, 0.40m
D: 2.0m, 1.0m, 0 .50m
E: 2.0m, 1.0m, 0.67m

Can u tell, which year it is from? and the answer?

 

[Ahmedraza73]

Can u tell, which year it is from? and the answer?

june 83

 

[snowbrood]

Can any solve my question?
A taut wire is clamped at two points 1.0m apart.It is plucked near one end.which are three longest wavelengths on the vibrating wire?
A: 1.0m, 0.50m, 0.25m
B: 1.0m, 0.67m, 0.50m
C; 2.0m, 0.67m, 0.40m
D: 2.0m, 1.0m, 0 .50m
E: 2.0m, 1.0m, 0.67m

FUNDAMENTAL SECOND HARMONIC AND THIRD HARMONIC ARE
WAVELENGTH=2L WAVELENGTH=L WAVELEGNTH 2/3L RESPECTIVELY NOW PLUG IN IN L AND U WILL GET UR ANS WHICH IS E

​

 

[snowbrood]

Hi. I have a doubt in Photoelectric effect. I don't understand how the photoelectric current reduces when we reduce the wavelength.
Qs. 7C http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s11_qp_41.pdf

Forget the photoelectric effect for a moment. Think about what is meant by the intensity of the radiation of the target surface.

Intensity = power / [target area]
Rearranges to:
power = intensity * area

If you are keeping the intensity constant, and the area of the photo-target is constant, then the power of the incident radiation must also be constant.

Each photon brings with it a certain amount of energy. If you reduce the wavelength, you increase the amount of energy carried by each photon.

The energy delivered = (energy of a photon) * (number of photons)

power = energy / time

So:
power = (energy of a photon) * (number of photons) / time

If the power is constant, and the energy of a photon is increased, then (number of photons / time) must decrease.

Now we are back to the photoelectric effect.
Fewer photons/s = fewer electrons/s = smaller current.

EDIT:

Nope!

The charge on an electron is fixed.
The total charge delivered to the photo-anode = (charge on electron ) * (number of electrons)

Electric current = [charge] / [time]

Current = (charge on electron ) * (number of electrons)/(time)

If you have fewer electrons/second emitted by the photo-surface, you have a smaller current.

How quickly the electrons travel does not change that. (this is what my friend said i got no idea about this)

 

[Light Yagami]

Why is the answer A:-

 

[Dug]

Why is the answer A:-
View attachment 22199

If the forces 3N and 4N are applied at right angles, their R = 5N. The remaining 5N can be applied in the opposite direction to R, the resultant of 3N and 4N, which will give the minimum resultant force 0.

 

[salvatore]

http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_w11_qp_22.pdf
Please help me with no. 1 (b). I do not understand how to interpret and draw the graph.
An explanation and drawing will really be appreciated.
Thanks!

 

[Light Yagami]

Why is the answer D:-

 

[Hassan Ali Abid]

spring constant = force/extention

when force is 2N ext is 90mm and when force is 0N ext is 100mm ....

change in ext is 10mm =.01m

find its gradient :-
2/-.01 = -200 N .... ignore - sign because we have to find its magnitute which is 200 N so and is D (200 N)