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Physics: Post your doubts here!

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sagar65265

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ShreeyaBeatz said:
T

Look at the line which you said:
Putting these in the equation, we get

ρ = R * 1 m^2/1 m = R
So ρ = R
wont ρ =Rm?
Click to expand...

Yes, ρ = (R Ω) m, but those are a matter of units - the units for the final answer will be in Ωm, which are the units of resistivity (and it should be no other way, to be honest) but that's where the question becomes very specific - it states:

".....resistivity of a material is numerically equal to the resistance in ohms...."

so the units don't matter - the number you get in the end is what matters, i.e. the number you get as a result for the resistance will be the same number for the value of the resistivity. Only the number itself matters, so while the units are important in all situations, the question isn't concerned with the units. So fair play!

Hope this helped!
Good Luck for all your exams!
(and again, credit to Thought blocker for the symbols!)
 
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sagar65265 said:
Yes, ρ = (R Ω) m, but those are a matter of units - the units for the final answer will be in Ωm, which are the units of resistivity (and it should be no other way, to be honest) but that's where the question becomes very specific - it states:

".....resistivity of a material is numerically equal to the resistance in ohms...."

so the units don't matter - the number you get in the end is what matters, i.e. the number you get as a result for the resistance will be the same number for the value of the resistivity. Only the number itself matters, so while the units are important in all situations, the question isn't concerned with the units. So fair play!

Hope this helped!
Good Luck for all your exams!
(and again, credit to Thought blocker for the symbols!)
Click to expand...
Fair Play, dude. (y) Bas now no thanking. :)
 
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Ahmed H. Al-Neel said:
can anyone help me with question 15,21,23,35 ?
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s13_qp_11.pdf
Click to expand...
15)IDK

21)
pressure in liquids=hxdensityxg
pressure due to oil=Xx830x9.81
pressure due to water=(2000-x)x10000x9.81
since pressure et bottom =17.5MPa
[Xx830x9.81]+[(2000-x)x10000x9.81]=17.5MPa
solve x to give 1270 as the final answer

23)
F = kx so x = F/k
For A : x = 4/k
For B : x = 3/k
For C : x = 3k
For D : x = 8/3k
So here constant k is either being multiplied or divide, hence we take k as 1 if we would have addition or subtraction included, we take k as zero
Now put 1 instead k .. A = 4, B = 3, C = 3, D = 2.5 so A is the answer :)

35)IDK
 
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Anonymous981 said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s11_qp_11.pdf
Question number 15
Click to expand...
untitled-png.44397
 
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Ahmed H. Al-Neel said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w10_qp_12.pdf
questions 7,9,22,26,27,34 please!
Click to expand...
7)
Acceleration upwards is always -9.81 and downwards 9.81. As upward motion is positive, + multiplied ny - gives you -9.81. Vice versa with downward motion. - multiplied with +9.81. The magnitude stays the same as long as air resistance is neglected, and the sign depends on which direction you take as positive.

9)
initial momentum of the ball is 2mv before collision... if collision was perfectly elastic one, all the momentum would have been gained by the ball... and this would have made the change in the momentum equal to 4mv.. 2mv-(-2mv)... now it is given that collision is inelastic, it will lose some of its momentum to the wall.. so now change in momentum will be less than 4mv but cant be less than the initial momentum... so the answer is C.

22)
because since k is low for the first spring, the box will prevent it from breaking by over extending. Hence A

26)
We know that distance between two minima is given by λ/2 (example, distance b/w T and S is λ/2)
We also know that Microwave travels with the speed of light c i.e is 3 * 10^8 m/s
Given distance b/w each minima is 15 mm so total distance from T to P would be 15 * 4 = 60 mm

Now distance b/w:
T and S = λ/2,
S and R = λ/2
R and Q = λ/2
Q and P = λ/2
and them you get 2λ
so 2λ = 60*10^-3
hence λ = 0.03 m

We know that c = f * λ
So f = c / λ
f = ( 3 * 10^8 ) / ( 0.03 )
f=10GHz

27)
Let the distance between the double slit and the screen be 1m initally.
When the distance is increasd BY 2m the NEW distance is 3m.
Using the formula:
Wavelength= (fringe seperationx 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.

34)
voltage decreases linearly so its supposed to be B : as rho increases, there would be more steepness in graph
 
Ahmed H. Al-Neel

Ahmed H. Al-Neel

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Thought blocker said:
7)
Acceleration upwards is always -9.81 and downwards 9.81. As upward motion is positive, + multiplied ny - gives you -9.81. Vice versa with downward motion. - multiplied with +9.81. The magnitude stays the same as long as air resistance is neglected, and the sign depends on which direction you take as positive.

9)
initial momentum of the ball is 2mv before collision... if collision was perfectly elastic one, all the momentum would have been gained by the ball... and this would have made the change in the momentum equal to 4mv.. 2mv-(-2mv)... now it is given that collision is inelastic, it will lose some of its momentum to the wall.. so now change in momentum will be less than 4mv but cant be less than the initial momentum... so the answer is C.

22)
because since k is low for the first spring, the box will prevent it from breaking by over extending. Hence A

26)
We know that distance between two minima is given by λ/2 (example, distance b/w T and S is λ/2)
We also know that Microwave travels with the speed of light c i.e is 3 * 10^8 m/s
Given distance b/w each minima is 15 mm so total distance from T to P would be 15 * 4 = 60 mm

Now distance b/w:
T and S = λ/2,
S and R = λ/2
R and Q = λ/2
Q and P = λ/2
and them you get 2λ
so 2λ = 60*10^-3
hence λ = 0.03 m

We know that c = f * λ
So f = c / λ
f = ( 3 * 10^8 ) / ( 0.03 )
f=10GHz

27)
Let the distance between the double slit and the screen be 1m initally.
When the distance is increasd BY 2m the NEW distance is 3m.
Using the formula:
Wavelength= (fringe seperationx 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.

34)
voltage decreases linearly so its supposed to be B : as rho increases, there would be more steepness in graph
Click to expand...
thanks alooot i just forgot to ask u earlier, can u also do q.)25 ?
http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_w10_qp_12.pdf
 
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