Physics: Post your doubts here!

[OakMoon!]

 

[arlery]

Why isn't the speed of a proton affected by the presence of a magnetic field if travels through one?

 

[OakMoon!]

Why isn't the speed of a proton affected by the presence of a magnetic field if travels through one?

The force acting on the proton due to the magnetic field is perpendicular to the direction of travel of the proton, hence, only the direction changes and there is no effect on the speed. This is why the circular motion is produced.

 

[rz123]

Hi ! Can anyone tell me that how is work done a scaler quantity I mean the dimensions involve are Force and displacement both involves direction so....is there some rule like vector multiplied by a vector = scaler quantity. same kind of confusion regarding kinetic energy..

 

[abcde]

Hi ! Can anyone tell me that how is work done a scaler quantity I mean the dimensions involve are Force and displacement both involves direction so....is there some rule like vector multiplied by a vector = scaler quantity. same kind of confusion regarding kinetic energy..

I think that is so because the dot product of two vectors is always a scalar (that's way it is also called the scalar product).
Energy and work done are always positive and always scalars because it is their magnitude that's important, not the direction.

 

[rz123]

hmmmm Thank you. confusion reduced that the end product quantity matters and its unit, like in work done its joules & energy also in joules. direction not taken into consideration when keeping in mind the definition of work done n energy here..

 

[OakMoon!]

hmmmm Thank you. confusion reduced that the end product quantity matters and its unit, like in work done its joules & energy also in joules. direction not taken into consideration when keeping in mind the definition of work done n energy here..

LOL! No. Moment also has the same unit but represented as Nm but it is a vector quantity. You understood the logic given by 'abcde' in a different way. Try reading that again by first searching the net for the definitions of scalar product and vector product.

 

[rz123]

hehe very funny
vector product? :| can't find that. i understood through the logic of scaler product thing, i was going further.. :%)

 

[OakMoon!]

You don't need to know about scalar product and vector product unless you do them in Maths. Just remember that vector multiplied/divided by a vector will give you a scalar. As for moment it is a vector quantity as it's calculated using one vector (force) and one scalar (perpendicular distance).

 

[rz123]

yeah i got that a long while back JK Thank You

Emergency!
http://www.xtremepapers.com/CIE/Interna ... 7_qp_1.pdf

13, 22, 23(how and why not B for this mcq? ) , 37 (how can be the resistance same i mean in resistor Q there are a lot of wires, how will it have the same cross sectional area as resistor P) and last but not the least 40 plz help in all. take ur time thanks.

 

[Dayyanah]

13. look for the horizontal component for the force which will be 8cos 30. that the force then find torque
T=2Fr F is the force you got, r is half the distance between the two forces because tourqe will result in turning effect about the center.

 

[Dayyanah]

37. the formula for resistance is resistivity*length/area. both the resistors are made of copper so the resistivity is the same. note the question specifically mentions that the second resistor is made of equal length. and at the beginning it says that the amounts were the same. it is not the surface are that matters but the 2-D area that has to be used, which is unchanged in both. if im wrong, pls correct me

 

[unique840]

22. option A.
intensity = constant * (amplitude^2)
intensity is directly proportional to the square of amplitude.
10^12 = a^2
a = square root of 10^12
a = 10^6

 

[unique840]

23. option D.
it isnt B because option B states that the displacement is always zero. it is untrue as the displacement is just "instantaneously" zero.. when the wave will move forward there will be non-zero displacement.
there is maximum acceleration and maximum force at maximum points.. so option D is correct

 

[rz123]

^ Thank-you so much unique and dayyanah! It really helped :beer:

 

[unique840]

ur welcum

 

[Dayyanah]

ure welcome, nytym

 

[smartangel]

hey. can someone please explain what do we have to cover up for these points mentioned in the syllabus.notes for these would be great

-infer from appropriate experiments on electromagnetic induction:
• that a changing magnetic flux can induce an e.m.f. in a circuit
• that the direction of the induced e.m.f. opposes the change
producing it
• the factors affecting the magnitude of the induced e.m.f.
-explain simple applications of electromagnetic induction.

-show an understanding of how the force on a current-carrying
conductor can be used to measure the flux density of a magnetic
field using a current balance.

 

[rz123]

hi dears have no fears. kindly help
http://www.xtremepapers.com/CIE/Interna ... 7_qp_2.pdf

Q.5 b i , 4 c plz figure out the relevant concept which is missing and make me clear. thanks

 

[Silent Hunter]

http://www.xtremepapers.com/CIE/Interna ... 3_qp_1.pdf

anybody explain Q11 please

Thank you