Physics As question (Help)

YesterdaysDreams

Could someone answer these questions (In Steps) Please

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Reply 1

jaichandak

3) D
5) D
6) C

Are my answers correct?

Reply 2

Kyx

Original post by jaichandak

3) D
5) D
6) C

Are my answers correct?

D.
D.
A.

Reply 3

Onlineslayer

Original post by jaichandak

3) D
5) D
6) C

Are my answers correct?

Original post by Kyx

D.D.A.

Both are wrong.

It is

3.D
5.A
6.C

Reply 4

Kyx

Original post by Onlineslayer

Both are wrong.

It is

3.D
5.A
6.C

Maybe it is C...

Reply 5

jaichandak

omg I get it now. Rookie mistake :colondollar:

Reply 6

YesterdaysDreams

Original post by Onlineslayer

Both are wrong.

It is

3.D
5.A
6.C

Could you explain each one? please
as i don't get it

Reply 7

Username002

5) R=rho*a/l = rho*pi*r^2/l
d=2r
2d=4r
R=rho*pi*(4r)^2/l compared to R=rho*pi*(2r)^2/l

6)
1/R total = 1/r1 + 1/r2
r1= 4+4
r2= 4+4

Reply 8

Onlineslayer

Original post by Username002

5) R=rho*a/l = rho*pi*r^2/l
d=2r
2d=4r
R=rho*pi*(4r)^2/l compared to R=rho*pi*(2r)^2/l

6)
1/R total = 1/r1 + 1/r2
r1= 4+4
r2= 4+4

Pls correct your first equation.

Resistance is always proportional to length, not Area.

R = rho L/A

Reply 9

Jpw1097

Original post by YesterdaysDreams

Could someone answer these questions (In Steps) Please

3. Remember that a phase difference of 2π radians/360° is equal to a path difference of one wavelength, λ. Therefore a phase difference of 90° (π/2) radians is equal to a path difference of λ/4.

5. R = ρL/A

Therefore R α 1/A (that is, resistance is inversely proportional to the cross-sectional area) provided that the length and resistivity of the wire remain constant.

Area of a wire = πr² or A = πd²/4.

Therefore, if the diameter of the wire is doubled the area will increase by a factor of 4. Since R α 1/A, and area is 4 times greater, resistance must decrease by a factor of 4. Hence R_new = 0.25R. Therefore the answer is A.

6. You have to find the total resistance of the resistors in series first.

Remember, for resistors in series R_total = R₁ + R₂ + ... + R_n

So to find the resistance of the two 4Ω resistors in parallel you just simply add the individual resistance of each resistor.

R_total = 4Ω + 4Ω = 8Ω

Now, you can think of the circuit as two 8Ω resistors in parallel. Remember, for resistors in parallel 1/R_total = 1/R₁ + 1/R₂ + ... + 1/R_n

So to find the resistance of the two 8Ω resistors in parallel you have to use the formula

1/R_total = 1/8 + 1/8
1/R_total = 2/8 = 1/4

So to find R_total you just take the reciprocal of both sides, so R_total = 4Ω.

Reply 10

Absent Agent

Original post by Onlineslayer

Pls correct your first equation.

Resistance is always proportional to length, not Area.

R = rho L/A

You don't have the right to criticise when you didn't have the courage to help.

Reply 11

uberteknik

Original post by Onlineslayer

Pls correct your first equation.

Resistance is always proportional to length, not Area.

R = rho L/A

Rookie mistake.

Resistance is proportional to both length and area.

R=\rho\frac{L}{A}

If the length increases the resistance also increases.

If the area increases, the resistance falls.

Because the cross sectional area of the wire is a square function of the diameter, if the diameter doubles, the c.s.a. increases by a factor of 4.

Hence for the same length, the resistance must fall by a factor of 4.

(edited 8 years ago)

Reply 12

YesterdaysDreams

Thanks for the replies, I understand it now :smile:

Reply 13

Onlineslayer

Original post by uberteknik

Rookie mistake.

Resistance is proportional to both length and area.

R=\rho\frac{L}{A}

I don't understand your own definition of proportional. When the correlation is positive, we other say it is directly proportional, or we just say it is proportional. And when the correlation is negative, we categorically state that it is Inversely-proportional.

Be that as it may, the correct formulae speaks for itself and I'm sure the author of the incorrect formulae got my message square and clear.

And FYI, "rookie" mistakes are for a category of people.

Reply 14

Onlineslayer

Original post by Absent Agent

You don't have the right to criticise when you didn't have the courage to help.

and you are?

And when did correcting critical mistakes become "criticism"?

If you had the "courage" to scan through, you would have seen my earlier contribution. But of course, you decided to only attack as usual.

Reply 15

Absent Agent

Original post by Onlineslayer

and you are?

And when did correcting critical mistakes become "criticism"?

Since the time of making the impression of being knowledgeable but ignoring to explain the question and yet waiting for correcting other's answers.

If you had the "courage" to scan through, you would have seen my earlier contribution. But of course, you decided to only attack as usual.

Contribution? I'm sure what you did was nothing more than looking at a mark scheme to which the original poster can/had access. But yeah, you can call it an attack as a sophistical excuse to undermine my point.

Reply 16

uberteknik

Original post by Onlineslayer

Hello buddy. You were the one who stated proportional. I merely reflected your statement to make it easier for you to understand.

The message we get is you are up your own arse.

Good day.

Reply 17

lerjj

Original post by Onlineslayer

Just going to float by and state that your terminology is wrong - the word correlation is almost meaningless here. 'Proportional to' typically means is "Is equal to some constant times". This would probably include whatever you mean by a negative correlation (which I'm assuming you mean a negative slope).

Inversely proportional would usually mean

\propto \frac{1}{A}

. That's a hyperbola/reciprical relationship and is rarely what anyone means by "negative correlation".

As any good rookie knows, the more aloof your answer, the more likely it is to contain a mistkae

Reply 18

Onlineslayer

Original post by lerjj

\propto \frac{1}{A}

"A negative correlation means that there is an inverse relationship between two variables - when one variable decreases, the other increases. The vice versa is a negative correlation too, in which one variable increases and the other decreases. These correlations are studied in statistics as a means of determining the relationship between two variables."

Read more at http://examples.yourdictionary.com/negative-correlation-examples.html#hBfOGDgJL8bCDBA5.99

The dictionary is always there for us.

Y = -mx +c has a negative correlation relationship. Just as y = k/X does.
Just as in statistics, it's not about how straight the line is but the scattered plot of any points drawn.

Happy?

Reply 19

lerjj

Original post by Onlineslayer

Well I'm somewhat happy that you proved my point. Y = -mx would be described as proportional, yet has a 'negative correlation', whilst Y = 1/x is inversely proportional and does not fit the nice pattern.

Moreover, nobody uses the term correlation if you're talking about a simple theoretical relationship - correlations are for experimental (statistical) data. Proportionality is a different concept, and trying to explain one in terms of the other won't work very well.