Physics As estimation questions

[mominzahid]

Hi guys i've done some paper practice and i've seen some mcq's on estimation of different stuff like time taken to complete a 100 meter race or like the diamter of uranium atom or frequencies or wavelengths of different waves or like the young modulous of some material.. these are just some examples there are some other estimation questions too.. can someone please address this issue? it would be really helpful if someone provided any notes if available on this topic as it comprises of 1-2 marks in each paper. if not then can you please explain how to solve questions like these where u have to estimate and have no idea what the estimated value would be. also please answer the above estimates that i have written also.. please try to write back as soon as possible as i have my physics exam tomorrow..
any help appreciated.
Thanks guys.

 

[A.ELWY 7]

go to page 4...ull find what u r looking for

 

[mominzahid]

go to page 4...ull find what u r looking for

Hey thanks for the notes but i already had these.. :/ they're in not too much detail only some of the estimates are given... many questions i've seen they require estimates which are not stated here..for example this question:

For which quantity is the magnitude a reasonable estimate?
A frequency of a radio wave 500pHz
B mass of an atom 500µg
C the Young modulus of a metal 500kPa
D wavelength of green light 500nm

now to solve it i need to know all of the stated estimates... and none of these are given in these notes. :/

 

[A.ELWY 7]

Hey thanks for the notes but i already had these.. :/ they're in not too much detail only some of the estimates are given... many questions i've seen they require estimates which are not stated here..for example this question:

For which quantity is the magnitude a reasonable estimate?
A frequency of a radio wave 500pHz
B mass of an atom 500µg
C the Young modulus of a metal 500kPa
D wavelength of green light 500nm

now to solve it i need to know all of the stated estimates... and none of these are given in these notes. :/

a young modulus of a material is always a number times 10^11....for the waves..any frequency between 20Hz and 20000 Hz is only heard not more or less..and u mustmemorize the frequency, the wavelength and the order of the waves..starting from gamma rays to radio waves..for the mass of an atom..u need to know the mass of an electron, proton and a neutron..which are always givn in the 2nd page of any exam paper

 

[xhizors]

whats its ans i guess its D,, as in B mass of elec is around 1.9x10^-19 so adding them wont make it around 10^-6, as A.elwy 7 says ym of a metal is around 10^11 so no chance,, green lights wavelength is around 10^-7 and nm = 10^-9 so it is a ans as value is 500nm so two more zeros make it a nano meter lol

 

[xhizors]

http://www.telecomabc.com/p/prefix.html

this could help also include centi 10^-2 and peta 10^15

 

[mominzahid]

a young modulus of a material is always a number times 10^11....for the waves..any frequency between 20Hz and 20000 Hz is only heard not more or less..and u mustmemorize the frequency, the wavelength and the order of the waves..starting from gamma rays to radio waves..for the mass of an atom..u need to know the mass of an electron, proton and a neutron..which are always givn in the 2nd page of any exam paper

http://www.telecomabc.com/p/prefix.html

this could help also include centi 10^-2 and peta 10^15

whats its ans i guess its D,, as in B mass of elec is around 1.9x10^-19 so adding them wont make it around 10^-6, as A.elwy 7 says ym of a metal is around 10^11 so no chance,, green lights wavelength is around 10^-7 and nm = 10^-9 so it is a ans as value is 500nm so two more zeros make it a nano meter lol

thankyou so much that certainly cleared it up..
one more doubt.. i absolutely no idea of how a potentiometer works. what is its purpose and how does it works.. also the effects of making the changes like increasing/decreasing the length, increasing decreasing the voltage of the either batteries.. please explain all this to me and in as simple language as possible cuz in my pacific physics textbook i couldnt understand properly the concept of potentiometer.. help would be greatly appreciated thank you in advance.

 

[xhizors]

Potentionmeter(pm)
-pm can also be used as voltmeter as there is no current changes/losses occurs
-pm consist of a wire and a driver cell to also findout the emf of an unknown source also have galvanometer
- when there is no deflection in galvanometer at length of AY it means that the pd across the AY is equal to the emf of an unknown source..
- voltages dec along the lenth of the wire.
-Emf of the unknown source= (Ay/Ab)*Emf of the known source
it is same as Ex/Eo = Ay/Ab

u have to read more about its application and other uses lke how it is used to find to unknown emfs and how to use it while compairing pds
u have to see the circuit of how to compare for pds

heres some point to remember when using potetiometer to compare for pds
-when boths balanced point are found, the ratio of the lengths are the ratio of pds
-both resistors have same current flowing, ratio of pds is also the ratio of their resistance

hope this helps,, more if u once again read topic from ur book..

Plz pray that i and you both score A grade in tommorows paper Ameen..

 

[mominzahid]

Potentionmeter(pm)
-pm can also be used as voltmeter as there is no current changes/losses occurs
-pm consist of a wire and a driver cell to also findout the emf of an unknown source also have galvanometer
- when there is no deflection in galvanometer at length of AY it means that the pd across the AY is equal to the emf of an unknown source..
- voltages dec along the lenth of the wire.
-Emf of the unknown source= (Ay/Ab)*Emf of the known source
it is same as Ex/Eo = Ay/Ab

u have to read more about its application and other uses lke how it is used to find to unknown emfs and how to use it while compairing pds
u have to see the circuit of how to compare for pds

heres some point to remember when using potetiometer to compare for pds
-when boths balanced point are found, the ratio of the lengths are the ratio of pds
-both resistors have same current flowing, ratio of pds is also the ratio of their resistance

hope this helps,, more if u once again read topic from ur book..

Plz pray that i and you both score A grade in tommorows paper Ameen..

thankyou so much for this.... made it alot clear.. and InshAllah we will..

 

[mariam001]

ca anyone please explain question 36 in paper 11 may june 2017