Time to go through the sequence of questions you will be expecting. Get ready for next paper.
1. Mechanics - Errors,Vectors, kinematics, forces , circular motion, G-field (maybe),resonance and damping
2. Waves- Stationary, interference (p.d = ...) ,young double slit formula , diffraction grating formula.
3. Electricity and Magnetism - Current electricity, power in circuits, DC circuits, EM , Rectifiers
4. Modern Physics- Photoelectric effect, de broy wavelength, Energy levels, quantum tunnelling, semiconductors (energy band + depletion region ) ,activity and decay constant.
Showing posts with label Fundamentals series. Show all posts
Showing posts with label Fundamentals series. Show all posts
Wednesday, November 5, 2008
Saturday, November 1, 2008
Wavelength of electron
What is the wavelength of a 100 eV electron?
KE = 100 x 1.6 x10^-19 J
v = 5.93x 10^6 ms^-1
wavelength = h/p = 1.23 x10^-10 m
KE = 100 x 1.6 x10^-19 J
v = 5.93x 10^6 ms^-1
wavelength = h/p = 1.23 x10^-10 m
Gravitational potential
A satellite of mass 50 kg moves from a point where the potential is -20MJ kg^-1 to another point where the potential is -60 MJkg^-1 . In which direction does the satellite move and what is its change in potential energy?
Answer: It is moving closer to Earth and the loss in potential energy is 2000 MJ
Answer: It is moving closer to Earth and the loss in potential energy is 2000 MJ
Friday, October 31, 2008
Count rate vs activity
The detector of surface S, placed a distance r from the source receives a reading of 100 s^-1. What is the activity of the source?
This is similar to light source (intensity problems)
Activity = 100/S x (surface of sphere of radius r)
This is similar to light source (intensity problems)
Activity = 100/S x (surface of sphere of radius r)
Decay rate and mass
32P is a beta emitter with a decay constant of 5.6 x 10^-7 s^-1.For a particular application the initial rate of disintegration must yield 4.0 x 10^7 beta particles every second. What is the mass of pure 32P will give this decay rate?
32P means the mass of Na atoms (i mole) = 32 g.
Use formula A = (decay const) N, N = 7.14 x10^13.
mass = 7.14 x 10^13 x 32 x 1.66 x10^-27=3.79 x 10^-12 kg
or mass = 7.14 x 10^13x(32x10^-3)/6/02x10^23= 3.79 x 10^-12 kg
32P means the mass of Na atoms (i mole) = 32 g.
Use formula A = (decay const) N, N = 7.14 x10^13.
mass = 7.14 x 10^13 x 32 x 1.66 x10^-27=3.79 x 10^-12 kg
or mass = 7.14 x 10^13x(32x10^-3)/6/02x10^23= 3.79 x 10^-12 kg
Fundamentals : Ionisation energy
Ionisation energy can be read from n=1 , as n=infinity is E = 0. It is the energy required to escape from ground state . In the case of hydrogen n = 1 is E = - 13.6 eV, hence ionisation energy is 13.6 eV.
Fundamentals : STM
1. The space between the tip and the surface atoms represents the potential barrier.
2. Apply a potential between the tip and the surface.
3. Electron (wave property) obeys quantum rules and therefore can tunnel through the surface giving rise to tunnelling current.
4. The tunnelling current depends on the barrier gap.
5. Keep current constant by adjusting the gap as the tip moves across surface atoms.
6. By measuring the height of the gap as the tip moves over the entire surface , we can obtain the surface topography.
Summarize from pg 68
2. Apply a potential between the tip and the surface.
3. Electron (wave property) obeys quantum rules and therefore can tunnel through the surface giving rise to tunnelling current.
4. The tunnelling current depends on the barrier gap.
5. Keep current constant by adjusting the gap as the tip moves across surface atoms.
6. By measuring the height of the gap as the tip moves over the entire surface , we can obtain the surface topography.
Summarize from pg 68
Fundamentals: Internal energy
Internal energy is the sum of ke and pe of all the molecules.Internal energy can increase in the temperature increase(ke increase) or potential energy increase (molecules further apart)or more molecules present(N) .
Question in sample paper TYS pg 45.
16. The random ke of all the gas molecules inside a tyre of an aircraft is 63 kJ .
The translational ke of these molecules is 10 kJ.
The random pe of the molecules is - 2 kJ .
The pe due to the height of the aircraft is 4 kJ.
What is the internal energy of these molecules?
The internal energy of the molecules = ke (random) + Pe (random)= 63kJ + (-2kJ)= 61kJ
Table found on page 111 Q33 gives a clear information about ke , pe and internal energy of solid liquid and gas at different temperature. Temperature the same gives the same ke.
Question in sample paper TYS pg 45.
16. The random ke of all the gas molecules inside a tyre of an aircraft is 63 kJ .
The translational ke of these molecules is 10 kJ.
The random pe of the molecules is - 2 kJ .
The pe due to the height of the aircraft is 4 kJ.
What is the internal energy of these molecules?
The internal energy of the molecules = ke (random) + Pe (random)= 63kJ + (-2kJ)= 61kJ
Table found on page 111 Q33 gives a clear information about ke , pe and internal energy of solid liquid and gas at different temperature. Temperature the same gives the same ke.
Thursday, October 30, 2008
Tying up exam preparations
Time to go through the sequence of questions you will be expecting. Get ready to eat the big fish first!
1. Mechanics -kinematics,< momentum>, WEP, forces , circular motion, G-field or SHM(lots of formula..)
2. Waves- Stationary, interference (p.d = ...) ,young double slit formula , diffraction grating formula.
3. Electricity and Magnetism - E field(point source or uniform field), power in circuits, DC circuits, EM , EMI (explanation or calculation), AC (power & diode)
4. Modern Physics- Photoelectric effect, de broy wavelength, Energy levels, xray, tunnelling, semiconductors (energy band + depletion region ) , nuclear processes( energy calculation ,mass or BE way), activity and decay constant.
1. Mechanics -kinematics,< momentum>, WEP, forces , circular motion, G-field or SHM(lots of formula..)
2. Waves- Stationary, interference (p.d = ...) ,young double slit formula , diffraction grating formula.
3. Electricity and Magnetism - E field(point source or uniform field), power in circuits, DC circuits, EM , EMI (explanation or calculation), AC (power & diode)
4. Modern Physics- Photoelectric effect, de broy wavelength, Energy levels, xray, tunnelling, semiconductors (energy band + depletion region ) , nuclear processes( energy calculation ,mass or BE way), activity and decay constant.
Fundamentals: Resonance
Resonance can be a nuisance. How do you reduce the amplitude of oscillation or avoid resonance effect.
1. Add dampers to the system i.e increase damping
2. Alter natural frequency or driving frequency (if possible , depends on situation)
3. Reduce amplitude of driving force.
What can alter natural frequency of mass spring system? Change mass and spring constant.
What can alter natural frequency of a simple pendulum? Change the length of the string. Swing resemble simple pendulum.
1. Add dampers to the system i.e increase damping
2. Alter natural frequency or driving frequency (if possible , depends on situation)
3. Reduce amplitude of driving force.
What can alter natural frequency of mass spring system? Change mass and spring constant.
What can alter natural frequency of a simple pendulum? Change the length of the string. Swing resemble simple pendulum.
Fundamentals: No force on charge particle in B field
Give two situations in which a charged particle in magnetic field does not experience a magnetic force.
1. Charge not moving 2. charge moving parallel to Bfield direction.
1. Charge not moving 2. charge moving parallel to Bfield direction.
Fundamentals: Stationary wave or not??
Usually one source eg one loudspeaker at the end of a long glass tube . Large amplitude and low amplitude recorded. As in N05P3Q3 page 122
OR It can be one source eg one loudspeaker with reflector at the other end.
OR If 2 loudspeaker , it has to be facing each other and have the same frequency.
Basically stationary wave must be produced by two waves of the same frequency and speed traveling in the opposite direction.
OR It can be one source eg one loudspeaker with reflector at the other end.
OR If 2 loudspeaker , it has to be facing each other and have the same frequency.
Basically stationary wave must be produced by two waves of the same frequency and speed traveling in the opposite direction.
Fundamentals: Young double slit :Typical values
What is a , D and x values like? See q24 of page 122 which is N06P1 Q16.
Fundamentals: Sketch the temperature characteristic of a thermistor.
Learning outcome in pg 11. Required to know.
Graph shown in page 113 N06P2Q4
Graph shown in page 113 N06P2Q4
Fundamentals: Measuring the true acceleration due to gravity of value 9.83
When an object is released in an experiment to determine the acceleration due to gravity, there is also acceleration due to circular motion (for rotation ). Hence the acceleration measured in expt is less than the true value taken to be 9.83 Nkg-1.Express in formula :
m(9.83) = m g' + m (w2R)
g' = 9.83 - w2R
g' = 9.83 - 0.034 = 9.796 ms-2
m(9.83) = m g' + m (w2R)
g' = 9.83 - w2R
g' = 9.83 - 0.034 = 9.796 ms-2
Fundamentals: Question answered on apparent weight
Free body diagram of man on weighing scale: W-R=mw2R, R = W - mw2R, where R is the reading of weighing scale (apparent weight). W is the gravitational force.
If the rotation of the earth is more than 24 h then w is smaller . Hence the weighing scale shows a greater reading than before. In otherwords, the weighing scale reading is closer to true weight.
If the rotation of the earth is more than 24 h then w is smaller . Hence the weighing scale shows a greater reading than before. In otherwords, the weighing scale reading is closer to true weight.
Fundamentals :Question answered today
The polar satellite covers every part of the Earth as it moves from North pole and then pass South pole in less than 24 h (about 4hrs) and the Earth rotate too. It can keep track of migration from North to South hemisphere (as normally the case ) The geostationary satellite keeps looking at the same location on the Earth and its further hence image would not be any clearer than the polar which is very close to Earth (see period only few hours) .
Fundamentals : Question answered for today
One reaction gives 163MeV, means one atom of uranium 235 gives 163MeV. 10 kg consist of how many atoms? Take 10kg / 235x1.66x10-27 kg to give number of atoms N.
So N reactions (10kg) gives 163MeV x (10kg/235u)= 4.18x1027 MeV.
If use Na must find number of moles n= 10 kg/235x10-3kg =42.6 moles. Number of atoms N = 42.6x(6.02x1023). Energy released = 42.6x(6.02 x 1023) x 163 MeV= 4.18 x1027 MeV.
Both methods can be used depending on which makes more sense to you.
So N reactions (10kg) gives 163MeV x (10kg/235u)= 4.18x1027 MeV.
If use Na must find number of moles n= 10 kg/235x10-3kg =42.6 moles. Number of atoms N = 42.6x(6.02x1023). Energy released = 42.6x(6.02 x 1023) x 163 MeV= 4.18 x1027 MeV.
Both methods can be used depending on which makes more sense to you.
Wednesday, October 29, 2008
Fundamentals: Nuclear energy
If 235 Uranium releases 163 MeV of energy , how much energy is released by 10 kg of uranium?
E released= (163 MeV/235x1.66x10-27kg) x10kg = 4.18 x1027MeV = 6.69 x 1014 J
If the activity of a radioactive source is 8.7x 109 Bq , what is the power of the source ? The decay process releases 1.03 x 10-12 J .
Power = (8.7 x 109)(1.0 x 10-12 J)= 8.7 x 10-3 W
E released= (163 MeV/235x1.66x10-27kg) x10kg = 4.18 x1027MeV = 6.69 x 1014 J
If the activity of a radioactive source is 8.7x 109 Bq , what is the power of the source ? The decay process releases 1.03 x 10-12 J .
Power = (8.7 x 109)(1.0 x 10-12 J)= 8.7 x 10-3 W
Fundamentals; Avogadro number
Na is 6.02 x 1023 atoms or molecules that you would call one mole.
If you have 0.1 mole (n=0.1) then you would have 6.02 x 1022 atoms or molecules.
If you have 6.02 x 1021 atoms then you would have 0.01 mole
If the mass number is 12 for carbon , then one mole of carbon is 12 g , then 0.1 mole would be 1.2 g . The mass of one atom would be 12g/6.02x1023. The mass of N atoms = N multiply 12 g/6.02x1023.
You can also use this: mass of one atom of carbon as 12u where u =1.66x10-27kg. How many carbon atoms are there in 1 kg of carbon? N = 1kg divide by 12u.
Two formulas for ideal gas equation:
pV = nRT or pV = NkT
If you have 0.1 mole (n=0.1) then you would have 6.02 x 1022 atoms or molecules.
If you have 6.02 x 1021 atoms then you would have 0.01 mole
If the mass number is 12 for carbon , then one mole of carbon is 12 g , then 0.1 mole would be 1.2 g . The mass of one atom would be 12g/6.02x1023. The mass of N atoms = N multiply 12 g/6.02x1023.
You can also use this: mass of one atom of carbon as 12u where u =1.66x10-27kg. How many carbon atoms are there in 1 kg of carbon? N = 1kg divide by 12u.
Two formulas for ideal gas equation:
pV = nRT or pV = NkT
Subscribe to:
Posts (Atom)