- At the magnetic pole, the angle of dip is 90°
- A permanent magnet is made up of ferromagnetic material.
- At the centre of a bar magnet magnetism is zero, but at the poles maximum.
- A magnet is divided into two pieces of unequal lengths. Both the pieces will act as magnets.
- A sensitive magnetic instrument can be protected from outside magnetic field by placing it inside a box of soft iron.
- A magnet loses its magnetism on heating, by throwing repeatedly on earth or, when kept to itself for a long time.
- Leyden jar is a form of electrostatic capacitor and is used for storing electricity.
- A photocell is a device which converts light energy into electrical energy.
- Secondary cell stores energy in the form of chemical energy.
- If current flows in a circuit in only one direction, it is called direct current.
- If the electron flows alternately backward and forward, it is alternating current.
- The unit of current is ampere.
- Fuse wire is made of an alloy of tin & lead and its function is to break the circuit in case of overloading or, short circuiting.
- Fuse wire is always connected in series.
- To get maximum current, we should connect cells in series, if external resistance is very large and internal resistance is small.
- A solenoid is a coil of wire, wound uniformly on a cylinder.
- Generation of X-rays is an illustration of phenomenon of conversion of kinetic energy into radiant energy.
- When an electric bulb breaks, there is a mild bang due to the air rushing in to fill the evacuated space.
- A common fluorescent tube contains mercury vapour at low pressure.
- Atoms are the smallest possible unit of an element.
- Electron (e), Proton (P) and Neutron (N) are the fundamental particles.
- Cathod rays and Anode rays are the swarmers of electrons and protons respectively.
- Protons (P):
mass number 1
charge + 1 ( 1.67 x 10-19 columb)
mass = 1887 times of electron identical with a hydrogen ion (H+)
- Neutron (N) is the constituent of the nucleus of all element except hydrogen.
- Neutrons have no charge but in mass equal protons.
- Atomic no. = No. of electrons = No. of protons.
- Atomic weight = No. of protons + No. of neutrons.
- Isotopes have same atomic number but different atomic weight.
- Isobars have same atomic w eight but di fferent atomic numbers.
- Radioactivity is concerned with disintegration of nucleus.
- If N/P = 1, Nuclei will be stable. If N/P = above 1.6, Nuclei disintegrate.
- Every element with atomic number greater than that of lead (82) is radioactive.
- The three of the nine natural radioactive lighter elements are 6C14 (carbon), 19K40 (potassium) and 15P30 (phosphorus).
- With the emission of an alpha particle (the helium nuclei) the radioactive element loses 2P and 2N. For example, Uranium -238 (92U238) will change into Thorium -234 (90Th234).
- Emission of beta particle increases the atomic number of a radioactive element.
- Photons, the unit if gamma rays, have neither mass nor charge.
- Half-life is the time in which half the atoms of a particular radioactive element disintegrate.
- Iodin-131 has half-life 8 days means that its half of the given amount will disintegarate in 8 days.
- Large doses of gamma radiation can be used both to destroy cancer tumours in the body, and to sterilize anything like surgical instruments, food, etc.
- Arsenic-74 is used to detect tumours.
- Sodium-24, incorporated in the common salt, is used to detect blood clots in the circulatory system.
- I-131 is used to determine the activity of thyroid gland.
- Gamma radiation is used for therapy in place of Xray where deep penetration is needed.
- Gamma ray kills micro-organism and grain weevils and beetles.
- Sea-port authorities use radioactive silicon to study the movement of sand and mud in rivers and ports.
- Half-life property of a radioactive element facilitates the dating of a fossil rock.
- For calculating age of the sample, commonly used radioactive isotopes are Uranium-238, Uranium-235, Thorium-232, Rubidium-87, Potassium-40 and Carbon-14.
- Nuclear energy results from the conversion of mass into energy according to Einstein formula E = mc2
- Conversion of 1 kg. of an element results into 9 *1016 joules or, 25 billion kilowatt-hour of energy.
- Fission is the reaction in which a heavy nucleus when strikes with a neutron splits into two parts releasing energy.
- The equation for fission reaction is 0n1 + 92U235 → 56Ba141 + 36Kr92 + 30n1
- The fission of a single uranium atom releases about 200 MeV of energy.
- Fission of Uranium-235, Uranium-233 and Plutonium239 are easier than the other radioactive elements.
- Uranium-235 constitutes only 0.72 per cent of naturally occurring uranium (uranium-238 constitutes the rest).
- Separation of U-235 from natural uranium is by electromagnetic separation, thermal diffusion, centrifugation and gaseous diffusion. Gaseous diffusion is the most commonly used method.
- Uranium with an abundance of U-235 is known as enriched uranium.
- Moderators are used to slow down the fast moving neutrons resulting from fission reaction in the nuclear reactor.
- Moderators are—heavy water, beryllium, paraffin and graphite.
- Nuclear fusion is the source of energy of the Sun. Its equation is 41H1 → 2 He4 + 2 Positrons + Energy.
- Temperature needed for fusion reaction taking place is approximately 200 million Kelvins.
- Hydrogen bomb is an example of nuclear fusion reaction.
- Advantages of nuclear fusion reaction over fission are
(i) quantity of energy liberated is much greater,
(ii) the fuel, deuterium (D2) is easily available from sea water,
(iii) it has no radioactive waste after the completion of reaction.
- The disposal of radioactive waste (the by-product of fission reaction) are in the following ways—
(i) binding the wastes in a glasslike or ceramic substance because of very resistant to corrosion. Then place it in deep underground.
(ii) dispose the wastes in granite formations underground or under the sea floor, in frozen clay, and in salt domes.
- Fission bombs are measured in Kilotons of TNT or thousands of tons.
- Fusion bombs are measured in megatons of TNT or millions of tons.
- India’s research reactors include APSARA, a 1 MW swimming pool type reactor; CIRUS, a 40 MW reactor; PURNIMA, a 100 MW reactor.
- On May 18, 1974 India conducted Pok haran (Rajasthan) exploision at 8.05 a.m. at a depth of 100 metres.
- By Pokharan explosion India became the sixth nuclear power after USA, USSR, U.K. France and China.
- Cosmic radiation are from outer atmosphere and have greater penetrating power even than the gamma rays.
- Cosmic ray consists of mainly protons, but also electrons, positrons, alpha particles and a few nuclei of heavier atoms.
- Masons have masses between that of electrons and protons and may carry + 1, - 1 or, zero electron charges.
- Masons may break into some of the lighter particles or, simply get swallowed up in atomic nuclei.
- A group of heavier nuclear particles are called baryons.
- The heaviest nuclear particle so far known is No. 3245, said to be 3.5 times heavier than the proton.
- Geig er-Mul ler c o unter, the cl oud ch amber, the bubble chamber, the spark-chamber, the scintillation detector devices are used to measure the energy, charges, masses, etc. of variously charged atomic particles.
- Van de Graff Generator, the cyclotron, the synchrotron, the linear accelerator are the particl e accelerators.