Physics: Post your doubts here!

[biscuitbiscuit]

someone please explain ;

http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_w02_qp_2.pdf
'Q7 b (i)'

 

[BreakingBad]

someone please explain ;

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w02_qp_2.pdf
'Q7 b (i)'

E = Pt = V^2t/R Where V (pd) and (t) are constant in both the cases therefore:

E1/E2 = R2/R1
E1 = 1.1 * 10^5
R1 = 45
R2 = 15

Substitute the values into the equation. Answer is 3.67 * 10^4

 

[biscuitbiscuit]

E = Pt = V^2t/R Where V (pd) and (t) are constant in both the cases therefore:

E1/E2 = R2/R1
E1 = 1.1 * 10^5
R1 = 45
R2 = 15

Substitute the values into the equation. Answer is 3.67 * 10^4

Can u explain again, how did you get the formula 'E1/E2 = R2/R1'

 

[BreakingBad]

Can u explain again, how did you get the formula 'E1/E2 = R2/R1'

E = Pt = V^2t/R, since V and t are constant we can write this equation as:
E = k/R
So,
E is directly proportional to 1/R
So, can can conclude:
E1/E2 = R2/R1

 

[sara kamal]

Change in PE = GMm [1/(R+h1) - 1/(R+h2)]
Change in KE = 1/2m (v1^2 - v2^2)

Equate equations. m cancels. Substitute values of G, (R+h1), (R+h2), v1 and v2 and you'll get the correct answer.

i did this actually ,can u show me steps please..?

 

[BreakingBad]

i did this actually ,can u show me steps please..?

GMm [1/(R+h1) - 1/(R+h2)] = 1/2m (v1^2 - v2^2)
m cancels.
GM [1/(R+h1) - 1/(R+h2)] = 1/2 (v1^2 - v2^2)
Make M subject:
M = (v1^2 - v2^2)/2G[1/(R+h1) - 1/(R+h2)]
M = (5370^2 - 5090^2)/2*6.67*10^11 [1/(6.38+19.9)*10^6 - 1/(6.38+22.7)*10^6]
M = 2928800/13.34*10^-11 [3.66385*10^-9]
M = 2928800/4.88758*10^-19
M = 5.99*10^24 = 6*10^24

 

[sara kamal]

but

GMm [1/(R+h1) - 1/(R+h2)] = 1/2m (v1^2 - v2^2)
m cancels.
GM [1/(R+h1) - 1/(R+h2)] = 1/2 (v1^2 - v2^2)
Make M subject:
M = (v1^2 - v2^2)/2G[1/(R+h1) - 1/(R+h2)]
M = (5370^2 - 5090^2)/2*6.67*10^11 [1/(6.38+19.9)*10^6 - 1/(6.38+22.7)*10^6]
M = 2928800/13.34*10^-11 [3.66385*10^-9]
M = 2928800/4.88758*10^-19
M = 5.99*10^24 = 6*10^24

But why are we subtracting like 1/R,why not just directly R+h1 - R+h2?

sorry for trouble!

 

[BreakingBad]

but



But why are we subtracting like 1/R,why not just directly R+h1 - R+h2?

sorry for trouble!

The formula for P.E. = -GMm/r
r is the distance and it is in the denominator. In this case, r1 is R+h1 and r2 is R+h2.
Change in PE = final PE - Initial PE
= -GMm/r2 - (-GMm/r1)
= GMm/r1 - GMm/r2
Take GMm common:
GMm(1/r1 - 1/r2)

Oh and you cannot simply multiply the distances r1 and r2 on the right side during calculation without taking LCM as there is a - sign between them.

 

[sara kamal]

The formula for P.E. = -GMm/r
r is the distance and it is in the denominator. In this case, r1 is R+h1 and r2 is R+h2.
Change in PE = final PE - Initial PE
= -GMm/r2 - (-GMm/r1)
= GMm/r1 - GMm/r2
Take GMm common:
GMm(1/r1 - 1/r2)

Oh and you cannot simply multiply the distances r1 and r2 on the right side during calculation without taking LCM as there is a - sign between them.

Thank you sooo much !!

 

[hacker]

plz solve this !

 

[sara kamal]

http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_s09_qp_4.pdf

please explain Q11 b (3)

 

[BreakingBad]

plz solve this !

Intensity is directly proportional to Amplitude squared
Intensity is inversely proportional to distance squared.
Therefore:
A^2 = k/x^2
When x=r, A=8.
64 = k/r^2
k = 64r^2

When x = 2r, A=?
A^2 = 64r^2/(2r)^2
A^2 = 64/4
A = 4 um

 

[Galactic]

Why do magnets attract ferromagnetic materials only? Why not other materials as well?

 

[Hassan Ali Abid]

Why do magnets attract ferromagnetic materials only? Why not other materials as well?

Other materials dont have the proper alignment of north and south pole and the materials whose alignment cant be changed by the magnet are not attracted by the magnet.

 

[Galactic]

Other materials dont have the proper alignment of north and south pole and the materials whose alignment cant be changed by the magnet are not attracted by the magnet.

What exactly do you mean by "proper alignment" ? And why don't they have proper alignment? And why can a magnet change the alignment of iron but not of for example wood or paper?

 

[Hassan Ali Abid]

What exactly do you mean by "proper alignment" ? And why don't they have proper alignment? And why can a magnet change the alignment of iron but not of for example wood or paper?

thats what i meant with alignment ....when the magnetic substances are gets their proper alignment having proper direction of north and south pole then they are magnetized and thats the reason why they are attracted to the magnets..

 

[Nawal Mahmood]

Assalamualikum wr wb!
I'm stuck in this question and I was wondering if anyone could help me out a little bit.
Q: Monochromatic radiation of wavelength 546nm falls of a potassium surface of area 7.5cm ^2 in an evacuated chamber. intensity of surfave is 60Wm^2 and it may be assumed that 1% of the photons wmit electrons from the surface. what is the photoelectric current?
What I did is , found the intensity=power/area. power=energy/time. So, I found time this way and applied this time in the formula of , current=charge /time. I multilpied the charge with 19 bcuz that's the atomic no. of potassium.
I'm not getting the right answer which is 0.020 micro Amps. What am I doing wrong? Help?

 

[Nawal Mahmood]

Assalamualikum wr wb!
I'm stuck in this question and I was wondering if anyone could help me out a little bit.
Q: Monochromatic radiation of wavelength 546nm falls of a potassium surface of area 7.5cm ^2 in an evacuated chamber. intensity of surfave is 60Wm^2 and it may be assumed that 1% of the photons wmit electrons from the surface. what is the photoelectric current?
What I did is , found the intensity=power/area. power=energy/time. So, I found time this way and applied this time in the formula of , current=charge /time. I multilpied the charge with 19 bcuz that's the atomic no. of potassium.
I'm not getting the right answer which is 0.020 micro Amps. What am I doing wrong? Help?

 

[TheStallion-Reborn]

In AS physics, my teacher made me study projectile motion, but I cannot find it in the syllabus. Can anyone please clarify?

 

[sara kamal]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s11_qp_41.pdf

please explain Q9 and Q10c(2)