1) What is the first step in problem-solving? A) Writing code B) Debugging C) Understanding the problem D) Optimizing the solution Answer: C 2) Which of these is not a step in the problem-solving process? A) Algorithm development B) Problem analysis C) Random guessing D) Testing and debugging Answer: C 3) What is an algorithm? A) A high-level programming language B) A step-by-step procedure to solve a problem C) A flowchart D) A data structure Answer: B 4) Which of these is the simplest data structure for representing a sequence of elements? A) Dictionary B) List C) Set D) Tuple Answer: B 5) What does a flowchart represent? A) Errors in a program B) A graphical representation of an algorithm C) The final solution to a problem D) A set of Python modules Answer: B 6) What is pseudocode? A) Code written in Python B) Fake code written for fun C) An informal high-level description of an algorithm D) A tool for testing code Answer: C 7) Which of the following tools is NOT commonly used in pr...
ATOMIC PHYSICS
The charge of an electron was found to
be 1.602 × 10-19 coulomb.
Properties of Cathode rays
Cathode rays have the following properties:
1. They travel in straight lines.
2. Cathode rays possess momentum and kinetic energy.
3. Cathode rays produce heat, when allowed to fall on matter.
4. Cathode rays creates fluorescence when they strike a number of crystals, minerals and salts.
5. When cathode rays strike a solid
substance of higher atomic weight, X-rays are produced.
6. Cathode rays ionize the gas through which they pass.
7. Cathode rays affect the photographic plates.
8. The cathode rays are deviation from their straight line path by both electric and magnetic fields. The direction of deflection shows that they are negatively charged
particles.
9. Cathode rays travel with a velocity upto (1/10)th of the velocity of light.
10.Cathode rays comprises of electrons which are fundamental constituents of all atoms.
Properties of Canal rays
1. They are the flow of positive ions of the gas enclosed in the discharge tube. The mass of each ion is nearly equal to the mass of the atom.
2. They are distracted by electric and magnetic fields. Their deflection is opposite to that of cathode rays.
3. They travel in straight lines.
4. The velocity of canal rays is much lesser than the velocity of cathode rays.
5. They affect photographic plates.
6. These rays can produce fluorescence.
7. They ionize the gas through which they flow.
Atom models
1803, Dalton, showed that the matter is made up of extremely small particles called atoms. Prout (1815), proposed that all elements are made up of atoms of hydrogen
Thomson atom model
An atom is a sphere of positive charge own a radius of the order of 10-10m. The positive charge is uniformly
distributed over the entire sphere and the electrons are embedded in the sphere of positive charge. The total positive charge inside the atom is equal to the total negative charge carried by the electrons, so that every atom is electrically neutral
Rutherford’s α - particle scattering experiment
The scattering of the α - particles by a thin gold foil in order to investigate the structure of the atom. An α-particle is a positively charged particle having a mass equal to that of helium atom and positive charge in magnitude equal to twice the charge of an electron.
a. Atom may be regarded as a sphere of diameter 10-10m, but whole of the positive charge and almost the entire mass of the atom is concentrated in a small central core called nucleus having diameter of
about 10-14m.
b. The electrons in the atom were considered to be distributed around the nucleus in the empty space of the atom. If the electrons were at rest, they would be attracted and neutralized by the nucleus. To overcome this, Rutherford suggested that the electrons are revolving around the nucleus in circular orbits, so that the
centripetal force is provided by the
electrostatic force of attraction between the electron and the nucleus.
c. As the atom is electrically neutral, the total positive charge of the nucleus is equal to the total negative charge of the electrons in it.
Bohr atom model
a. An electron cannot revolve round the nucleus in all possible orbits. The electrons can revolve round the nucleus only in those allowed or permissible orbits for which the angular momentum of the electron is an integral multiple of h 2π (where h is Planck’s constant = 6.626 × 10-34 Js).
* These orbits are called stationary orbits or nonradiating orbits and an electron revolving in these orbits does not radiate any energy. If m and v are the mass and
velocity of the electron in a permitted orbit of radius r then angular momentum of electron = mvr =nh/2π, where n is called
principal quantum number and has the integral values 1,2,3 … This is called Bohr’s quantization condition.
b. An atom radiates energy, only when an electron jumps from a stationary orbit of higher energy to an orbit of lower energy. If the electron jumps from an orbit of energy E2 to an orbit of energy E1, a photon of energy hν = E2 – E1 is emitted. This condition is called Bohr’s frequency condition.r1 = 0.53Å This is called Bohr radius.
Spectral series of hydrogen atom
Electron in a hydrogen atom jumps from higher energy level to the lower energy level, the difference in energies of the two levels is emitted as a radiation of particular wavelength. It is called a spectral line. As the wavelength of the spectral line depends upon the two orbits (energy levels) between which the transition of electron takes place, various spectral lines are obtained.
(i) Lyman series
When the electron jumps from any of the outer orbits to the first orbit, the spectral lines emitted are in the ultraviolet region
n1 = 1, n2 = 2, 3…
(ii) Balmer series
When the electron jumps from any of the outer orbits to the second orbit, we get a spectral series called the Balmer series. All the lines of this series in hydrogen have their wavelength in the visible region.
n1 = 2, n2 = 3, 4…
(iii) Paschen series
This series contains of all wavelengths which are emitted when the electron jumps from outer most orbits to the third orbit
(iv) Brackett series
The series acquired by the transition of the electron from n2 = 5, 6... to n1 = 4 is called Brackett series. The wavelengths of these lines are in the infrared region.
(v) Pfund series
The lines of the series are obtained when the electron jumps from any state n2 = 6, 7... to n1=5. This series also located in the infrared region.
Excitation and ionization potential of an atom
The energy needed to raise an atom from its normal state into an excited state is called excitation potential energy of the atom. Hydrogen atom, the energy required to remove an electron from first orbit to its outermost orbit(n=∞) 13.6-0=13.6eV.This energy is known as the ionization potential energy for hydrogen atom
Sommerfeld atom model
In order to describe the observed fine structure of spectral lines, Sommerfeld
introduced two main modifications in Bohr’s theory.
(i) According to Sommerfeld, the way of an electron around the nucleus, in general, is an ellipse with the nucleus at one of its foci.
(ii) The velocity of the electron flowing in an elliptical orbit varies at different parts of the orbit. This causes the relativistic variation in the mass of the moving electron
X–rays
A German scientist, Wilhelm Roentgen, in 1895, discovered X–rays X-rays are electromagnetic waves of short wavelength in the range of 0.5 Å to 10 Å. For the discovery of X–rays Roentgen was awarded Nobel prize in 1901.
Production of X–rays – Modern Coolidge tube
X–rays are produced, when fast moving electrons strike a metal target of suitable material. The basic requirement for the production of X–rays are: (i) a source of electrons, (ii)effective means of accelerating the electrons and (iii) a target of suitable material of high atomic weight.
Soft X–rays and Hard X–rays
X–rays are of two forms : (i) Soft X–rays and (ii) Hard X–rays
(i) Soft X–rays
X–rays having wavelength of 4Å or above, have lesser frequency and hence lesser energy. They are called soft X –rays due to their less penetrating power. They are produced at comparatively low potential difference.
(ii) Hard X–rays
X–rays having less wavelength of the order of 1Å have high frequency and hence high energy. Their penetrating power is high, therefore they are called hard X–rays. They are created at comparatively high potential difference.
Properties of X–rays
1. X–rays are electromagnetic waves of very less wave length. They travel in straight lines with the velocity of light. They are invisible to eyes.
2. They undergo reflection, refraction, interference, diffraction and polarisation.
3. They are not deflected by electric and magnetic fields. This shows that X-rays do not have charged particles.
4. They ionize the gas through which they flow.
5. They affect photographic plates.
6. X–rays can penetrate through the substances which are opaque to ordinary light e.g. wood, flesh, thick paper, thin sheets of metals.
7. When X–rays fall on certain metals, they liberate photo electrons (Photo electric effect).
8. X-rays have destructive effect on living tissue. When the human body is exposed to X-rays, it causes sores, redness of the skin, and serious injuries to the tissues
and glands. They destroy the white corpuscles of the blood.
9. X–rays do not pass through heavy metals such as lead and bones. If such objects are kept in their way, they cast their shadow
Applications of X–rays
X–rays have a number of applications. Some of them are listed below:
Medical applications
* X–rays are being mainly used for detecting fractures, tumours, the presence of foreign matter like bullet etc., in the human body.
* X–rays are also used for the diagnosis of tuberculosis, stones in gall bladder, kidneys etc.
* Many types of skin diseases, malignant sores, tumours and cancer have been cured by controlled exposure of X-rays of
suitable quality.
* Hard X–rays are used to destroy tumours very deep inside the body.
Industrial applications
a. X–rays are used to detect the defects or flaws within a material
b. X–rays can be used for testing the homogeneity of welded joints, insulating materials etc.
c. X-rays are used to analyse the structure of alloys and the other composite bodies.
d. X–rays are also used to study the structure of materials like rubber, cellulose, plastic fibres etc.
Scientific research
1. X–rays are used for studying the structure of crystalline solids and alloys.
2. X–rays are used for the identification of chemical elements including determination of their atomic numbers.
3. X–rays can be used for analyzing the structure of complex molecules by
examining their X–ray diffraction pattern.
Laser
Some sources have been developed, which are highly coherent known as LASER. The word ‘Laser’ stands for Light Amplification by Stimulated Emission of Radiation.
Characteristics of laser
The laser beam (i) is monochromatic. (ii) is coherent, with the waves, all correctly in phase with one another, (iii) does not diverge at all and (iv) is extremely intense
Applications of laser
Due to large coherence, high intensity, laser beams have wide applications in various branches of science and engineering.
Industrial applications
a. The laser beam is used to drill extremely fine holes in diamonds, hard sheets etc.,
b. They are also used for cutting thick sheets of hard metals and welding.
c. The laser beam is used to vapourize the unwanted material during the manufacture of electronic circuit on semiconductor chips.
d. They can be used to test the quality of the materials.
Medical applications
a. In medicine, micro surgery has become possible due to narrow angular spread of the laser beam.
b. It can be used in the treatment of kidney stone, tumour, in cutting and sealing the small blood vessels in brain surgery and retina detachment.
c. The laser beams are used in endoscopy.
d. It can also be used for the treatment of human and animal cancer.
Scientific and Engineering applications
1. Since the laser beam can stay on at a single frequency, it can be modulated to transmit large number of messages at a time in radio, television and telephone.
2. The semiconductor laser is the best light source for optical fiber communication.
3. Narrow angular spread of the laser beam makes it a very useful tool for microwave communication. Communication with earth satellites and in rocketry. Laser is also used in accurate range finders for detecting the targets.
4. The earth-moon distance has been measured with the help of lasers.
5. It is used in laser Raman Spectroscopy
6. Laser is also used in holography (three dimensional lensless photography)
7. Laser beam can determine precisely the distance, velocity and direction as well as the size and form of the objects by means
of the reflected signal as in radar.
Holography
* A three dimensional image of an object can be formed by holography. In ordinary
photography, the amplitude of the light wave is recorded on the photographic film. In holography, both the phase and amplitude of the light waves are recorded on the film. The resulting photograph is called hologram.
MASER
* The term MASER stands for Microwave Amplification by Stimulated Emission of Radiation. The working of maser is similar to that of laser.