Physics: Post your doubts here!

[Lyfroker]

According to lenz's law, emf tends to oppose the change causing it, so here, sketch will just have opposite peaks, and when current is constant, no emf on sketch, since no emf is induced when there is no change

Thanks

 

[Lyfroker]

http://freeexampapers.com/A-Level/Physics/CIE/2002-Nov/9702_w02_qp_4.pdf

Q#2(b) & Q#5

 

[nehaoscar]

http://maxpapers.com/wp-content/uploads/2012/11/9702_w14_qp_11.pdf
question 9 please.
Idk how to do these momentum questions. I'll be indebted to you if someone could explain how to tackle questions of this sort please.

the formula for momentum is
m1u1 + m2u2 = m1v1 + m2v2
Now since the direction of the velocity is different for the two trucks initally, we will substract

m1u1 - m2u2 = m1v1 - m2v2
3mv - 2mv = 3mv1 + mv1 -- velocity after collision for both trucks is same as they have stuck together and so velocity is also in the same direction, therefore you add
Simplify this to give
mv = 4mv1
Rearrange to get
v1 = mv/4m -- the m's cancel therefore
v1 = v/4
which is option A

 

[nehaoscar]

http://maxpapers.com/wp-content/uploads/2012/11/9702_w14_qp_11.pdf
And question 10 also please.

The question says that the plane descends at constant velocity , so it's in equilibrium
Just join the arrows shown on the diagram end to end with all the arrows facing in the same direction and it will give you the answer
as option D

 

[nehaoscar]

w14question paper 11 question 28 please explain

The charge is held in equilibrium by it's weight and electric field
The direction of the electric field is always from positive to negative

So the direction of the forces are:
electric field = downwards
gravitational acceleration = downwards
Since both these forces are acting downwards, yet the charge is held in equilibrium, it means that it is attracted to the positive charge (so the direction of this force will be upwards to balance the downwards forces), hence the drop itself id negatively charged.

This means it's either option A or B

Now charge/mass column
E = F/Q so
Q = F/E

and
F = mg so
m = F/g

Charge / mass = F/E divided by F/g
= g/E

Therefore the answer is option B

 

[anasaziz18]

Assalamualaikum,
I have 2 doubts which are from phy p4. Please help me with them.
Here are the questions.

Please solve them asap.

 

[imahnoor]

i need help with p2 o/n 14 q1 c, q2 iii

 

[princess Anu]

can somebody plz do this..
ans is the 60 degree & 3/4

 

[MYLORD]

can somebody help me with this bullet point

 

[nehaoscar]

can somebody help me with this bullet point
View attachment 52791

Homogeneous means that the units on both sides cancel out
In the first example, the units cancel
s = 2ut + at^2
m = (m/s x s) + (m/s^2 x s^2) -- x represents multiplication
m = m + m
m = 2m
And so the m's cancel and no units are left on either side
Although the equation therefore is homogeneous, the equation itself is incorrect:
The actual formula for the equation is:
s = ut + 0.5at^2
and NOT
s = 2ut + at^2

But if you take the correct equation, you can see that it definitely is homogeneous.

 

[MYLORD]

Homogeneous means that the units on both sides cancel out
In the first example, the units cancel
s = 2ut + at^2
m = (m/s x s) + (m/s^2 x s^2) -- x represents multiplication
m = m + m
m = 2m
And so the m's cancel and no units are left on either side
Although the equation therefore is homogeneous, the equation itself is incorrect:
The actual formula for the equation is:
s = ut + 0.5at^2
and NOT
s = 2ut + at^2

But if you take the correct equation, you can see that it definitely is homogeneous.

thnx

 

[anasaziz18]

 

[anasaziz18]

can somebody plz do this..
ans is the 60 degree & 3/4

for the first part of the ques, sin90=1 right? and sin30 is 0.5.
So, think of the polarised wave as a sine curve where max amplitude is at 90 degrees. Now, if at 30 degrees we get half the max amplitude then the polariser should be rotated by 60 degrees since (90-30=60).

Next part...

 

[princess Anu]

but where did sin90 come from

for the first part of the ques, sin90=1 right? and sin30 is 0.5.
So, think of the polarised wave as a sine curve where max amplitude is at 90 degrees. Now, if at 30 degrees we get half the max amplitude then the polariser should be rotated by 60 degrees since (90-30=60).

Next part...View attachment 52799

 

[anasaziz18]

but where did sin90 come from

First the wave is polarised by polariser P. Then the wave vibrates in only one plane ryt? So we can consider it as a sine wave which has its max at 90 degrees. Or if you consider it to be a cosine function then, at 0 degree it is max and at 60 degree, its half since (cos60=0.5) so from 0 to 60 degrees, the Q has to be rotated.

 

[princess Anu]

First the wave is polarised by polariser P. Then the wave vibrates in only one plane ryt? So we can consider it as a sine wave which has its max at 90 degrees. Or if you consider it to be a cosine function then, at 0 degree it is max and at 60 degree, its half since (cos60=0.5) so from 0 to 60 degrees, the Q has to be rotated.

ohkayy but i don't get it when do we have to relate waves to such graphs :/

 

[princess Anu]

can somebody ans this ques
describe how u would demonstrate that a sound wave of wavelength 0.1m emotted from a loudspeaker can be diffracted.(4)
what diagram needs to be made?

 

[ali_jaliawala]

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[ali_jaliawala]

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[The Sarcastic Retard]

can somebody ans this ques
describe how u would demonstrate that a sound wave of wavelength 0.1m emotted from a loudspeaker can be diffracted.(4)
what diagram needs to be made?

http://www.thestudentroom.co.uk/showthread.php?t=2580146&page=46