A2 Physics | Post your doubts here

[miss irfan]

bt cnt it be like that they have different k.e

the questions remains. why dividing it by 2 at all?

 

[SkyPilotage]

Question June 2002
6 a) I am having problems with the first part of the graph!
Please upload a picture of it, and I will reply whether I agree or not!

 

[hassam]

WELL I DONT UNDERSTAND THE PURPOSE OF DIODE 2......EVEN IF THERE IS A BACK EMF CAN DIODE D1 PROTECT OPAMP cos it will be in reverse biased

 

[angelicsuccubus]

Okay I got it. the answer in the marking scheme is the half-life of the source is very long or decay constant is very small. I think they mean that the half life is so huge that there will be a constant emission throughout the period before reaching half life.

oh and I noticed .. >>>>>>

3.5x10^6 40
______ = ____
s days

 

[hassam]

Question June 2002
6 a) I am having problems with the first part of the graph!
Please upload a picture of it, and I will reply whether I agree or not!

i have not got the paper........cn u post pic here.....and by the way i want to discuss rectification graphs

 

[hassam]

well if i have to do graph of p.d across diode hw will it look like

 

[SkyPilotage]

WELL I DONT UNDERSTAND THE PURPOSE OF DIODE 2......EVEN IF THERE IS A BACK EMF CAN DIODE D1 PROTECT OPAMP cos it will be in reverse biased

D1 is there to avoid any output current from the op amp when the op amp output is at a negative voltage. If the op amp has no negative voltage power supply, then there will be no need for D1.

D2 is there to prevent a high voltage, generated by the coil when power is removed, from damaging the op amp.

When the op amp applies a positive current going down into the coil, a current is flowing in the coil. This current generates a magnetic field around the coil and core. If the op amp output suddenly switches off (i.e. goes to zero volts, or goes negative), then the magnetic field will start to collapse at a high rate. As the magnetic lines of flux fall back through the coil windings as the field collapses, a voltage is developed across the coil. The voltage is such that the top end of the coil (at the op amp) will go to a positive voltage. Without D2, this voltage can go high enough so that the op amp can be damaged. Diode D2 shunts the current to ground so that the voltage can't go higher than about 1 volt. This also allows some current to continue to flow in the coil as the magnetic field decays, which also allows the voltage that would be developed by the coil to be reduced. This also makes it take a few more milliseconds for the relay to finish its mechanical movement.

Source:- http://en.allexperts.com/q/Electrical-Engineering-1356/2011/4/Protection-Diode-Relay.htm

 

[hassam]

The ms is wrong for this question.

hmmmm whats the problem in ms?

 

[SkyPilotage]

i have not got the paper........cn u post pic here.....and by the way i want to discuss rectification graphs

For the rectification graphs, which year was it?
And the question asked for the voltage across diodes right?
Please refer back where "user" [ thoroughly interpreted the problem with lots of diagrams ]

 

[miss irfan]

please solve my confusion too

 

[surajsingh143]

http://www.xtremepapers.com/communi...notes-of-physics-according-to-syllabus.14888/ go to this thread for your complete A2 notes....

 

[namename]

When do you use electric potential/x graph and electric field strength/x graph?
S08 4 (unlike charges) and w11 42 4 (like charges) even if the graph looks the same...

 

[Idris]

Hmm im not sure I agree, cz electrons have a particele nature.
It is the electrons which have the wave-particle dualty.

As well as the light, this experiments was specifically designed to demonstrate the particulate nature of light not electrons. The particulate nature of electrons is shown by milikian's oil drop experiment.

 

[SkyPilotage]

When do you use electric potential/x graph and electric field strength/x graph?
S08 4 (unlike charges) and w11 42 4 (like charges) even if the graph looks the same...

June 2002 Question 6 a) did you find the answer? Please post a pic of it, and I will reply if I agree.

 

[SkyPilotage]

As well as the light, this experiments was specifically designed to demonstrate the particulate nature of light not electrons. The particulate nature of electrons is shown by milikian's oil drop experiment.

I thought milikan's showed the quanitsation of electrons?

 

[SkyPilotage]

As well as the light, this experiments was specifically designed to demonstrate the particulate nature of light not electrons. The particulate nature of electrons is shown by milikian's oil drop experiment.

you are absolutely right that it provides evidence for particulate nature of light.
but are you sure it doesnt show the particulate nature of electrons too?
For example if there is a question that asks to design an experiment to prove particulate nature of electrons, What experiment do we draw?

Wikipedia :- "The photoelectric effect requires photons with energies from a few electronvolts to over 1 MeV in high atomic number elements. Study of the photoelectric effect led to important steps in understanding the quantum nature of light and electrons and influenced the formation of the concept of wave–particle duality"

Are you sure electrons are not proven as particles from the photoelectric effect?

 

[user]

But, like how do you know?

E is the rate of change of magnetic flux density. from T1 to T2 variation in B is constant i.e the gradient is constant . so a horizontal line is sketched . same goes for t2 to t3 but in opposite direction ..
you simply have to sketch the gradient per unit time for the above graph .. get it ?

aoa! isn't E supposed to be 'negative' d((phi)/dt

 

[SkyPilotage]

As well as the light, this experiments was specifically designed to demonstrate the particulate nature of light not electrons. The particulate nature of electrons is shown by milikian's oil drop experiment.

Btw thank you for the correction, much appreciated !

 

[mybch]

Guys, do we have to know about the nuclear fission reactor?

 

[OakMoon!]

hmmmm whats the problem in ms?

The question clearly asks for mean power so the Irms current should be used in the calculations and not the peak current as they have done in ms.