NASA Seeks Ideas For New Prize Challenges

WASHINGTON -- The Innovative Partnerships Program at NASA Headquarters in Washington is offering an opportunity for the public to help shape the prize challenges the agency offers to America's future citizen-inventors.
For the next six weeks, ideas for new Centennial Challenge prize competitions may be proposed for NASA's consideration. Creative ideas are sought from industry, colleges, universities, private organizations and the public. The ideas will be posted on the NASA Web site to stimulate additional creativity. Some selected proposals may be formulated into future prize competitions starting in 2010, pending availability of prize purse funding.
Centennial Challenges is NASA's program to award cash prizes to independent inventors for significant advances in technologies of interest to NASA and the nation. The program encourages innovation throughout the private sector, including small businesses, college/university teams and individuals. The program seeks creative solutions from diverse and unconventional sources.
Centennial Challenges address robotic lunar excavation, super-efficient aircraft, reusable rocket-powered vehicles, wireless power transmission, super-strength materials and improved astronaut gloves. Ideas must be received by Sunday, Nov. 8, 2009, for this round of consideration. For instructions about how to submit ideas, visit:

http://www.nasa.gov/offices/ipp/innovation_incubator/cc_future.html

 

 

http://www.nasa.gov/home/hqnews/2009/sep/HQ_09_225_NASA_IPP_Ideas.html

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Huygens' Principle

Huygens’ Principle is based on the following assumptions:

• Each point on the primary wavefront acts as a source of secondary wavelets, sending out disturbance in all directions in a similar manner as the original source of light does.

• The new position of the wavefront at any instant (called secondary wave front) is the envelope of the secondary wavelets at that instant.

Laws of Reflection on Wave Theory

• Consider any point Q on the incident wavefront PA.

• When the disturbance from P on incident wavefront reaches point , the disturbance from point Q reaches .

• If c is velocity of light, then time taken by light to go from point Q to (via point K) is given by,

• In right-angled ΔAQK,

∠QAK = i

∴ QK = AK sin i

• In right-angled ,

Substituting these values in equation (1),

The rays from different points on incident wavefront will take the same time to reach the corresponding points on the reflected wavefront, if ‘t’ given by equation (ii) is independent of AK.

∴ AK (sin i − sin r) = 0

sin i − sin r = 0

sin i = sin r

i = r

i.e., the angle of incidence is equal to the angle of refraction.

Also, the incident ray (LA or), reflected ray (or ), and the normal (AN) − all lie in the same plane.

Refraction On The Basis Of Wave Theory

• Consider any point Q on the incident wavefront.

• Suppose when disturbance from point P on incident wavefront reaches point on the refracted wavefront, the disturbance from point Q reaches on the refracting surface XY.

• Since represents the refracted wavefront, the time taken by light to travel from a point on incident wavefront to the corresponding point on refracted wavefront should always be the same. Now, time taken by light to go from Q to will be

• In right-angled ΔAQK, ∠QAK = i

∴ QK = AK sin i … (ii)

• In right-angled

… (iii)

• Substituting (ii) and (iii) in equation (i),

• The rays from different points on the incident wavefront will take the same time to reach the corresponding points on the refracted wavefront i.e., t given by equation (iv) is independent of AK. It will happen so, if

This is the Snell’s law for refraction of light.

Electron Emission and Photoelectric Effect

• The phenomenon of emission of electrons from the surface of a metal is called electron emission.

• Work function − A certain minimum amount of energy is required to be given to an electron to pull it out from the surface of the metal. This minimum energy required by an electron to escape from the metal surface is called the work function of the metal.

• The minimum energy required for the electron emission from the metal surface can be supplied to the free electrons by any one of the following physical processes:

  • Thermionic emission − By suitable heating, sufficient thermal energy can be imparted to the free electrons to enable them to come out of the metal.

  • Field emission − By applying a very strong electric field to a metal, electrons can be pulled out of the metal.

  • Photoelectric emission − When light of suitable frequency illuminates a metal surface, electrons are emitted from the metal surface.

Photoelectric Effect

• The apparatus consists of an evacuated glass or quartz tube, which encloses a photosensitive plate C and a metal plate A.

• The window W will allow the light of a particular wavelength to pass through it.

• When a monochromatic radiation of suitable frequency obtained from source S falls on the photosensitive plate C, the photoelectrons are emitted from C, which get accelerated towards the plate A(kept at positive potential).

• These electrons flow in the outer circuit, resulting in the photoelectric current. Due to this, the microammeter shows a deflection.

• Factors affecting photoelectric current:

  • Effect of intensity of light on photocurrent − The number of photoelectrons emitted per second is directly proportional to the intensity of incident radiation.
    

  • Effect of potential on photoelectric current

• • Keep plate A at some positive accelerating potential with respect to plate C and illuminate plate Cwith light of fixed frequency ν and fixed intensity I₁.
    It is found that photoelectric current increases with increase in accelerating potential. At some stage, for a certain positive potential of plate A, all the emitted electrons are collected by plate Aand the photoelectric current becomes maximum or saturates. This maximum value of photoelectric current is called saturation current.
    The minimum negative potential V₀ given to plate A with respect to plate C at which the photoelectric current becomes zero is called stopping potential or cut off potential. If e is the charge on the photoelectron, then
    
    Where,
    m = Mass of photoelectron
    v_max = Maximum velocity of emitted photoelectron

  • Effect of frequency of the incident radiation − Taking radiations of different frequencies but of same intensity, the variation between photoelectric current and potential of plate A is obtained and shown in graph given below.

From the graph, we note:

(i) The value of stopping potential is different for radiation of different frequency.

(ii) The value of stopping potential is more negative for radiation of higher incident frequency.

(iii) The value of saturation current depends on the intensity of incident radiation, but is independent of the frequency of the incident radiation.

• Graph between stopping potential and the frequency of the incident radiation:

From the graph, we note:

(i) For a given photosensitive material, the stopping potential varies linearly with the frequency of the incident radiation.

(ii) For a given photosensitive material, there is a certain minimum cut-off frequency ν₀ (called threshold frequency), for which the stopping potential is zero.

• Laws of photo-electric emission:

  • For a given metal and frequency of incident radiation, the number of photoelectrons ejected per second is directly proportional to the intensity of the incident light.

  • For a given metal, there exists a certain minimum frequency of the incident radiation below which no emission of photoelectrons takes place. This frequency is called threshold frequency.

  • Above the threshold frequency, the maximum kinetic energy of the emitted photoelectron is independent of the intensity of the incident light, but depends only upon the frequency (or wavelength) of the incident light.

  • The photoelectric emission is an instantaneous process.

Alpha Particle Scattering and Rutherford's Nuclear Model of an Atom

The experimental set up used by Rutherford and his collaborators, Geiger and Marsden, is shown in the above figure.

Observations − A graph is plotted between the scattering angle θ and the number of α-particles N (θ), scattered at ∠θ for a very large number of α-particles.

Conclusions:

• Most of the alpha particles pass straight through the gold foil.

• Only about 0.14% of incident α-particles scatter by more than 1.

• About one α-particle in every 8000 α-particles deflects by more than 90°.

Explanation

• In Rutherford’s model, the entire positive charge and most of the mass of the atom are concentrated in the nucleus with the electrons some distance away.

• The electrons would be moving in orbitals about the nucleus just as the planets do around the sun.

• The size of the nucleus comes out to be 10⁻¹⁵ m to 10⁻¹⁴ m. From kinetic theory, the size of an atom was known to be 10⁻¹⁰ m, about 10000 to 100,000 times larger than the size of the nucleus. Thus, most of an atom is empty space.

• The trajectory of an alpha particle can be computed employing Newton’s second law of motion andCoulomb’s law for electrostatic force of repulsion between the alpha particle and the positively charged nucleus.

The magnitude of this force is

Where,

Ze − Charge of gold nucleus

2e − Charge on alpha particle

r − Distance between α-particle and the nucleus

Alpha particle trajectory

Trajectory traced by an α-particle depends on the impact parameter b of collision. The impact parameter is the perpendicular distance of the initial velocity vector of the α-particle from the centre of the nucleus.

• For large impact parameters, force experienced by the alpha particle is weak because. Hence, the alpha particle will deviate through a much smaller angle.

  When impact parameter is small, force experienced is large and hence, the alpha particle will scatter through a large angle.

• Electron orbits

Let

F_c − Centripetal force required to keep a revolving electron in orbit

F_e − Electrostatic force of attraction between the revolving electron and the nucleus

Then, for a dynamically stable orbit in a hydrogen atom,

F_c = F_e

K.E. of electron in the orbit,

From equation (i),

Potential energy of electron in orbit,

Negative sign indicates that revolving electron is bound to the positive nucleus.

∴ Total energy of electron in hydrogen atom

Atomic Masses and Composition of Nucleus

• The mass of an atom is so small that it is inconvenient to express it in kilograms.

• The unit in which atomic and nuclear masses are measured is called atomic mass unit (amu).

• One amu is defined as 1/12^th of the mass of an atom of isotope.

Avogadro’s number = 6.023 × 10²³

∴Mass of 6.023 × 10²³ atoms of C¹² = 12 g

• Atomic masses can be measured using a mass spectrometer.

• The different types of atoms of the same element which exhibit the same chemical properties, but differ in mass are called isotopes.

Nucleus

• The nucleus has the positive charge possessed by the protons. Atomic number is Z. The total charge on an atomic electron is (− Ze) while the charge of the nucleus is (+ Ze).

• The composition of a nucleus is described using the followings terms and symbols.

Z = Atomic number = Number of protons

N = Neutron number = Number of neutrons

A = Mass number = Z + N = Total number of protons and neutrons

• Nuclear species can be shown by the notation

  Where, X = Chemical symbol of the species

• Nuclides with the same mass number (A) are called isobars, and nuclides with the same neutron number (N) are called isotones.

Classification of Metals, Conductors, and Semi-conductors

• Metals − Possess very low resistivity (or high conductivity)

• Semi-conductors − Possess resistivity or conductivity intermediate to metals and insulators

• Insulators − Possess high resistivity (or low conductivity)

• Semi-conductors are of two types:

  • Elemental semi-conductor − Example: Si and Ge

  • Compound semi-conductor − Example: CdS, GaAs, CdSe, InP, etc.

• Energy band diagram of metals or conductors
  

  • Conduction band is partially filled and the valence band is partially empty or the conduction and valence balance overlap.

  • Due to overlap, electrons can easily move into the conduction band. This situation makes a large number of electrons available for electrical conduction.

  • When the valence band is partially empty, electrons from their lower levels can move to higher levels making conduction possible.

• Energy band diagram for insulators
  

  • Large band gap E_g exists. (E_g > 3eV)

  • Since there are no electrons in the conduction band, no electrical conduction is possible.

  • The electron cannot be excited from the valence band to the conduction band by thermal excitation.

• Energy band diagram for semi-conductors
  

  • Energy band gap Eg is small. (Eg < 3eV)

  • At room temperature, some electrons from valence band cross the energy gap and enter the conduction band.

Elements of Communication System

• Communication is the act of transmission of information.

• Communication system has three essential elements − transmitter, medium/channel, and receiver.

• Receiver and transmitter are located at different places and the channels connect them.

• Transmitter converts the message signal produced by the source of information into a form suitable for transmission through the channel.

.

Some important terms

• Transducer − It converts one form of energy into another.

• Signal − It is information converted into electrical forms, which is suitable for transmission.

• Noise − It refers to the unwanted signal that tends to disturb the transmission and processing of message signal in a communication system.

• Transmitter − It processes the incoming message signal and makes it suitable for transmission through a channel to the receiver.

• Receiver − It extracts the desired message signal from the received signal at the output of the channel.

• Attenuation − It is the loss of strength of a signal while propagating through a medium.

• Amplification − It is the process of increasing the amplitude of a signal using an electronic circuit called the amplifier.

• Range − It is the largest distance between a source and a destination up to which the signal is received with sufficient strength.

• Bandwidth − It is the portion of the spectrum occupied by the signal.

• Modulation − It is a process of superimposing a high frequency wave (carrier) on the low frequency message/ information signal, which cannot be transmitted to long distance without the help of the carrier.

• Demodulation − It is the process of retrieval of information from the carrier wave at the receiver.

• Repeater − It is a combination of receiver and a transmitter. It is used to extend the range of a communication system.

Displacement Current

• According to Ampere’s circuital law, the line integral of the magnetic field around any closed path or circuit is equal to μ₀ times the total current

• In the calculation of magnetic field, Ampere’s circuital law brought in several contradictions. When a different surface was used to find the magnetic field, the result was different.

• It was concluded that a term was missing from the Ampere’s circuital law—the electric field. This electric field passes the surfaces between the plates of the capacitor used.

• Each plate of a capacitor has an area A, and a total charge Q. Then, the magnitude of the electric field E is,

• Using Gauss’ law, the electric flux Φ_E through the surface is calculated as

• As the charge Q on the capacitor plates changes with time, there is a current,

i = dQ/dt

This is the missing term in Ampere’s circuital law.

• The current carried by conductors due to the flow of charges is called conduction current, and the current (new term) due to the changing electric field is called displacement current or Maxwell’s displacement current.

• Total current, i = Conduction current (i_c) + Displacement current (i_d)

• Outside the capacitor plate, i = i_c, and inside the capacitor plate, i = i_d

• Ampere−Maxwell law is given as

The total current passing through any surface, of which the closed loop is the perimeter, is the sum of the conduction and displacement current.