PHYSICS

 ABSOLUTE  REFRACTIVE INDEX  The absolute refractive index of a medium is the ratio of speed of light in vacuum and the speed of light in the medium. Absolute refractive index = Speed of light in vacuum or air                                                     Speed of light in the medium  For example, A.r.i of glass = speed of light in vacuum/speed of light in glass  3×10⁸/2×10⁸= 3/2=1.5 Its value is equal or more than 1. For vacuum or air, its value is 1. So its minimum value is 1. RELATIVE REFRACTIVE INDEX  The relative refractive index of a medium (a) with respect to another medium (b) is the ratio of speed of light in medium (b) and the speed of light in medium (a). Relative refractive index of  (a) wrt (b)=Speed of light in medium (b )                        ...

 Answer:  Inner pulleys are smaller than others to eradicate the frictional force between the ropes and inner pulleys while in use.

Spanner has a long handle. Why? Answer: When perpendicular distance between the force and the axis of rotation is large, smaller force is required to produce  the desired torque.

Terminal voltage of a dry cell is 1.3 V. It means that the cell can supply 1.3J of energy to move unit positive charge across its terminals in the external circuit connected to the cell.

Emf of a dry cell is 1.5 V. It means that the cell can supply 1.5 joule of energy to move 1 coulomb of charge all around the circuit ( outside and inside  the cell).

  MCB stands for  a) miniature circuit board  b) miniature circuit band c) miniature circuit breaker d) miniature circuit blocker Ans: c

Q1: What is radioactivity? A:  The  phenomenon of spontaneous emission of alpha particle or beta particle and gamma rays  from an unstable nucleus is called radioactivity.   Q2: When does a nucleus  become unstable ? A: When the number of neutrons become much more than that of protons. Q3: Which part of the atom takes part in radioactivity ? A: Nucleus Q4: What happens to the radioactive behaviour of a radioactive sample if it is chemically oxidized ? A: The radioactive behaviour does not change. As oxidation is the chemical change, it does not affect the nuclear activity. Q5: How does the atomic number and mass number change if a radioactive nucleus releases one alpha particle ? A: Atomic number decreases by 2 and mass number decreases by 4 Q6: How does the atomic number and mass number change if a radioactive nucleus releases one beta particle? A: Atomic number increases by 1 and mass number does not change.