Physics: Post your doubts here!

[Thought blocker]

Which formula is applied in this?!


Suchal Riaz Thought

Which formula is applied in this?!


Suchal Riaz Thought

C ?

 

[Thought blocker]

Electrons are negatively charged, and as such they will move from an area of lower potential to an area of higher potential. Also, they will move away from the negative terminal and towards the positive terminal (conventional current moves in the opposite direction, and in reality this flow of electrons is the current that actually transfers energy across the circuit).

Therefore, the current will go from the terminal on the right to the top-right corner of the circuit, move to the bottom right (point Y), move across the resistor to (point X) and then back to the positive terminal of the battery. Therefore, the current will be from Y to X (i.e. option C or D).

Furthermore, if the current is 4.8 Amperes, using the formula

Q = I * t

(Where Q is the charge that flows through a point in "t" seconds when a current of I Amperes is flowing)
we can say that

I = Q/t

So the current is equal to the rate of flow of charge past a point. Okay, so this has units Coulombs/Second, which is what we want (answer is also in same units).
So if the current is 4.8 Amperes, the rate of flow of charge is 4.8 Coulombs/Second.
How much is this? Let's see.

The charge on any 1 electron is 1.6 * 10⁻¹⁹ Coulombs. Therefore, to make up 1 Coulomb, we need 1/(1.6 * 10⁻¹⁹) = 6.25 * 10¹⁸ electrons.
But if 1 Coulomb is 6.25 * 10¹⁸ electrons per second, 4.8 Coulombs should be 4.8 * (6.25 * 10¹⁸) electrons per second, right?

Carrying out this calculation, we get 4.8 * (6.25 * 10¹⁸) = 30.0 * 10¹⁸ = 3.0 * 10¹⁹ electrons/second.

This flows in the direction of Y to X, therefore our answer must be A.

Hope this helped!
Good Luck for all your exams!

http://www.allaboutcircuits.com/vol_1/chpt_1/7.html
Electron flow is frm y to x so C

 

[Suchal Riaz]

Which formula is applied in this?!


Suchal Riaz Thought

there are a series of formulae to apply in this one. you must make sense first.
current = rate of flow of CHARGE
I = Q/t
charge of electron is e = 1.6E-19
(Q/t )/Q=1/t
if we divide I(total charge per time) by charge of one single electron we get number of electrons.
and the direction of current is from + to - but the direction of flow of current is from negative to positive.

 

[Suchal Riaz]

View attachment 44975

density = mass/volume
ρ=m/V
mass = ρV
----
both masses are same. the second liquid has twice density. so for mass to be same the volume must be half. total volume = 1.5 times initial volume.
final mass = twice the initial mass.
final ρ = 2m/1.5V = 4/3 ( m/V) = 4/3 ρ

 

[Suchal Riaz]

View attachment 44976

he is moving up at rate of 50cm/s means 0.5m/s
his mass is 80KG so his weight is almost 785N
power = work done per second= Force * distance/second = 785*0.5=392=0.39KW

 

[Suchal Riaz]

View attachment 44977 View attachment 44978

if he is at constant speed there is no resultant force so all forces cancel out so
air resistance = weight
kv=mg
v=mg/k
kinetic energy = 1/2 mv² = 1/2 m (mg/k)² = 1/2 m³g²/k² = m³g²/2k²

 

[Thought blocker]

he is moving up at rate of 50cm/s means 0.5m/s
his mass is 80KG so his weight is almost 785N
power = work done per second= Force * distance/second = 785*0.5=392=0.39KW

LOL I GOT 392 then I thought I might had made some mistake LOL

 

[Thought blocker]

if he is at constant speed there is no resultant force so all forces cancel out so
air resistance = weight
kv=mg
v=mg/k
kinetic energy = 1/2 mv² = 1/2 m (mg/k)² = 1/2 m³g²/k² = m³g²/2k²

Acha!!

 

[Suchal Riaz]

View attachment 44977 View attachment 44978

m1g is weight at one side. m2g is weight at other side. their difference is balanced by motor.
so the resultant force is m1g - m2g = g(m1-m2)
motor provide the same amount of force to keep the resultant = o
power = Fv = g(m1-m2)*v

 

[Thought blocker]

View attachment 44977 View attachment 44978

Ok..

 

[Asad Moosvi]

http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_w10_qp_12.pdf

Q 27 anyone?

 

[Thought blocker]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w10_qp_12.pdf

Q 27 anyone?

Let the distance between the double slit and the screen be 1m initially.
When the distance is increased BY 2m the NEW distance is 3m.
Using the formula:
Wavelength= (fringe seperation x distance between the double slits)/ distance between the screen and the slits.
Wavelenght=600nm=600x10^-9m.
Fringe seperation= 3mm= 3x10^-3m
Distance between screen and slits= 3m (1+2)
Distance between the double slit=?
Put these values in the formula, the final answer is 6x10^-4m =0.6mm
Hence the answer is B.

 

[Princess Raven]

Can someone explain q 17,29,30 of mj 12 v 12
And question 40,20,7,3 of mj 07
PLZZ

 

[Thought blocker]

Can someone explain q 17,29,30 of mj 12 v 12
And question 40,20,7,3 of mj 07
PLZZ

s12_s12
17)
At the bottom height is zero so mgh = zero
now going upwards..
2 block has height = 1 so mg1h
3 block = mg2h
4 block = mg3h
Sum up P.E ans is 6mgh

29)
c = f * λ
We know f = 1 / t
so c = 1 / t * λ
t = λ / c
now it took 3 wavefronts to reach XY to P
so t = 3λ / c

30)
Its a standing wave, so the 33cm is the distance between two nodes. The wavelength thus becomes .66m. F = 330/0.66 = 500. T = 1/500 = 0.002s = 2ms. B is the right answer

s07_1
Suchal Riaz
me gtg

 

[Asad Moosvi]

Let the distance between the double slit and the screen be 1m initially.
When the distance is increased BY 2m the NEW distance is 3m.
Using the formula:
Wavelength= (fringe seperation x distance between the double slits)/ distance between the screen and the slits.
Wavelenght=600nm=600x10^-9m.
Fringe seperation= 3mm= 3x10^-3m
Distance between screen and slits= 3m (1+2)
Distance between the double slit=?
Put these values in the formula, the final answer is 6x10^-4m =0.6mm
Hence the answer is B.

I know that, but why did you assume the initial distance between the double slits and the screen to be 1m? If we assume something else, we'll get a different answer.

 

[MYLORD]

http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_s10_qp_11.pdf q 5,16,20,27,

 

[Suchal Riaz]

Can someone explain q 17,29,30 of mj 12 v 12
And question 40,20,7,3 of mj 07
PLZZ

3:
simple. the speed must have units m/s
in (a) √(gλ)=(m²/s²)^½ = m/s
no need to check rest of them
7:
O level vectors: x=v-u
v-u = at
so x=at

20:
All i can do is visualise which parts are bending in what way. X and Y are being stretched but Z is being pressed/compressed.
X and Y experience tension while Z experiences compression. just visualise.
40:
the particle which completes acceleration with the lowest speed must have had lowest acceleration as the distance is same.
F is not the same. force directly proportional to charge. acceleration = F/m so acceleration will depends on charge and mass. A ∝charge/mass
so find charge to mass ratio. the one with smallest ratio has lowest acceleration therefore lowest speed at the end.
(a)1/1=1
(b)2/4=0.5
(c)3/7=0.428...
(d)4/9=0.44...
smallest is (c)

 

[Suchal Riaz]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w10_qp_12.pdf

Q 27 anyone?

x=dλ/a

in case 1,
1E-3=d600E-9 / a
so d=1667a
in case 2:
3E-3=(d+2)*600E-9 / a
a=(d+2)*600E-9 / 3E-3
a= (1667a + 2)2E-4
a-0.333a=4E-4
a=4E-4 / 0.667
=6E-4m=0.6mm
this was the only way it came in my mind. maybe ZaqZainab or someone else can tell a shorter way. if no shortway comes into your mind atleast do complete it through complete procedure.

 

[Asad Moosvi]

x=dλ/a

in case 1,
1E-3=d600E-9 / a
so d=1667a
in case 2:
3E-3=(d+2)*600E-9 / a
a=(d+2)*600E-9 / 3E-3
a= (1667a + 2)2E-4
a-0.333a=4E-4
a=4E-4 / 0.667
=6E-4m=0.6mm
this was the only way it came in my mind. maybe ZaqZainab or someone else can tell a shorter way. if no shortway comes into your mind atleast do complete it through complete procedure.

I solved it the same way now, but this takes too long

 

[..sacrifice4Revenge..]

x=dλ/a

in case 1,
1E-3=d600E-9 / a
so d=1667a
in case 2:
3E-3=(d+2)*600E-9 / a
a=(d+2)*600E-9 / 3E-3
a= (1667a + 2)2E-4
a-0.333a=4E-4
a=4E-4 / 0.667
=6E-4m=0.6mm
this was the only way it came in my mind. maybe ZaqZainab or someone else can tell a shorter way. if no shortway comes into your mind atleast do complete it through complete procedure.

E denotes?
i dnt get this :/