A combination of two thin lenses in contact behave as converging lens of focal length 80 cm if one of the lense is convrging lens of focal length 20 cm, the power of other lens will be
Explanation.
f= focul length of combination of two lenses
f1= focul length of ist lens
f2= focul length of 2nd lens
As 1/f =1/f1 + 1/f2
1/80 = 1/20 + 1/f2
1/f2 = 1/80 - 1/20
f2 = -26.66cm
= -0.266 m
As Power of lens P= 1/f (where f will be in meters)
So
P=1/-0.266
= -3.75D
Showing posts with label Physics. Show all posts
Showing posts with label Physics. Show all posts
Friday 29 August 2014
Some MCQs of Physics and Chemistry.
Q1)when the aircraft concorde is moving in horizontal plane at const speed 650 m/s its turning circle has radius of 80 km wat is ratio of centripetal force to the weight of air craft?
Ans.
Q2)when 0.24 gm of magnesium is reacted with excess HCl what volume of gas librated at RTP
Ans.
Q3)In mixture of NO and CO2 initialy containing 4 mol of NO and 0.9 mol of CO2 reaction ocur acording to NO+CO2>NO2+CO at eq 0.1 mol of CO2 was presnt what is Kc
Ans.
Q4)a box of mas m =6 kg slid with speed v=4 m/s acros frictionless flor it sudenly explodes into 2 pieces one piece with mass m1 =2kg moves in same direction with speed v1=8 m/s find velocity of 2nd piece
Ans. as momentum before collision= momentum after collision
for m2 ,m=m1+m2 6=2+m2 m2=4kg so 6(4)=2(8)+4(x) 8=4x x=2m/s
Q5)Q2) on groud the gravitational force on satelite is W wat is gravitational force on satelite when at height R/50 where R is radius of earth
Ans. On the ground, the distance (from the centre of the Earth) is R. In orbit, the distance is R+R/50 or (51/50)R. The force is (ETA: inversely) proportional to the square of the distance so the multiplier you want is (50/51)^2 ~=0.96W
Q6)equal weights of methane and hydrogen are mixed in an an empty container at 25 degre centegrad the fraction of total presure exerted by hydrogen is.
Ans. apply mole fraction formula by daltons law of partial pressure
as moles fraction=no of moles of components/no of total moles let no of moles H2= n/2 let no of moles of CH4=n/16 total moles = n/2 + n/16 =9n/16 so mole fraction of pressure exerted byH2= n/2 ÷ 9n/16 = n/2 × 16/9n =8/9 ans
Ans.
Q2)when 0.24 gm of magnesium is reacted with excess HCl what volume of gas librated at RTP
Ans.
Q3)In mixture of NO and CO2 initialy containing 4 mol of NO and 0.9 mol of CO2 reaction ocur acording to NO+CO2>NO2+CO at eq 0.1 mol of CO2 was presnt what is Kc
Ans.
Q4)a box of mas m =6 kg slid with speed v=4 m/s acros frictionless flor it sudenly explodes into 2 pieces one piece with mass m1 =2kg moves in same direction with speed v1=8 m/s find velocity of 2nd piece
Ans. as momentum before collision= momentum after collision
for m2 ,m=m1+m2 6=2+m2 m2=4kg so 6(4)=2(8)+4(x) 8=4x x=2m/s
Q5)Q2) on groud the gravitational force on satelite is W wat is gravitational force on satelite when at height R/50 where R is radius of earth
Ans. On the ground, the distance (from the centre of the Earth) is R. In orbit, the distance is R+R/50 or (51/50)R. The force is (ETA: inversely) proportional to the square of the distance so the multiplier you want is (50/51)^2 ~=0.96W
Q6)equal weights of methane and hydrogen are mixed in an an empty container at 25 degre centegrad the fraction of total presure exerted by hydrogen is.
Ans. apply mole fraction formula by daltons law of partial pressure
as moles fraction=no of moles of components/no of total moles let no of moles H2= n/2 let no of moles of CH4=n/16 total moles = n/2 + n/16 =9n/16 so mole fraction of pressure exerted byH2= n/2 ÷ 9n/16 = n/2 × 16/9n =8/9 ans
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Tuesday 6 May 2014
How to solve Physics problems:
1- Numerical problems of physics are not the same as the problems in
the mathematics. So do not try to memorise only the formulas and
equations without understanding the concepts of the topic related to the
problems.
2- Try to picture that have been said in the numerical problems. So read the problem carefully and don’t try to read like you are running out of time.
3- You must start to solve numerical problems with very easy, formula based, and “very short type” or “short type answer” questions. It will help you to learn the formula and basic concepts used in the problem and it will make you more enthusiastic towards problem-solving and strategy-making person for all physics problems.
4- You should never underestimate the Very Short Answer or Short Answer type questions because these questions are like learning key-board before you start to play piano.
5- For bigger problems try to draw a diagram with what have been given in the question.
6- Write down what you know and what you are trying to find out. In simple problems you may just do it in your mind but for more difficult problems it is very useful wherever you have to find out two, three or more results.
2- Try to picture that have been said in the numerical problems. So read the problem carefully and don’t try to read like you are running out of time.
3- You must start to solve numerical problems with very easy, formula based, and “very short type” or “short type answer” questions. It will help you to learn the formula and basic concepts used in the problem and it will make you more enthusiastic towards problem-solving and strategy-making person for all physics problems.
4- You should never underestimate the Very Short Answer or Short Answer type questions because these questions are like learning key-board before you start to play piano.
5- For bigger problems try to draw a diagram with what have been given in the question.
6- Write down what you know and what you are trying to find out. In simple problems you may just do it in your mind but for more difficult problems it is very useful wherever you have to find out two, three or more results.
A way to Memorizing Maths and Physics Formulas
Memorizing Math and Physics Formulas
1)..Math and Physics problems are not meant to be studied under stress. Relax your mind. By doing this, you will be able to focus more on your task.
2)..Many people think that once they take a glance at a formula, it is in their mind, but when they wake up the next day, they are shocked to realize that the formula leaked out during the night. This is why it is a good idea to practice solving a problem with the formula without looking it up. You must do this as many times as you can. Repetition leads to Memorization.
3).. Put the raw units of each variable into the formula and see if you can get the units of the answer.
4)..Understand How the Formula is structured. You already have a decent gut feeling about the concept. Make sense of the formula. For instance, a = F / m. F is on the top of the fraction. That makes sense, since if you exert more force on an object, it will speed up more quickly. Mass is on the bottom of the fraction, since more mass means more inertia, making the object more difficult to accelerate. The opposite formula (a = m / F) does not make sense. Using this incorrect formula, a strong force (large number on the bottom of the fraction) would cause a smaller acceleration, which does not make sense.
5).. Find a small book and put down all those formulas. Keep the book at your back pocket and try to review them anytime you feel like you are missing something. This will bring back the memories of what you have learned, making those jaw-breaking formulas stick into your mind forever.
1)..Math and Physics problems are not meant to be studied under stress. Relax your mind. By doing this, you will be able to focus more on your task.
2)..Many people think that once they take a glance at a formula, it is in their mind, but when they wake up the next day, they are shocked to realize that the formula leaked out during the night. This is why it is a good idea to practice solving a problem with the formula without looking it up. You must do this as many times as you can. Repetition leads to Memorization.
3).. Put the raw units of each variable into the formula and see if you can get the units of the answer.
4)..Understand How the Formula is structured. You already have a decent gut feeling about the concept. Make sense of the formula. For instance, a = F / m. F is on the top of the fraction. That makes sense, since if you exert more force on an object, it will speed up more quickly. Mass is on the bottom of the fraction, since more mass means more inertia, making the object more difficult to accelerate. The opposite formula (a = m / F) does not make sense. Using this incorrect formula, a strong force (large number on the bottom of the fraction) would cause a smaller acceleration, which does not make sense.
5).. Find a small book and put down all those formulas. Keep the book at your back pocket and try to review them anytime you feel like you are missing something. This will bring back the memories of what you have learned, making those jaw-breaking formulas stick into your mind forever.
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