Short Answer TypeGive two important precautions that should be taken while handling radioactive materials.
i) What is the name given to atoms of a substance which have the same atomic number but different mass numbers?
ii) What is the difference in the atomic structure of such atoms?i) What is meant by free elctrons?
ii) Why are they generally not able to leave the metallic surface?
iii) Suggest one way by which these electrons could be made to leave the metal surface.
In a cathode ray tube why is the:
i) filament made of tungsten?
ii) cathode plate coated with oxide of barium or strontium?
iii) thick glass screen coated with barium platinocyanide?
Long Answer TypeAn object of mass 'M’ is allowed to fall freely from point A as shown in the figure. Calculate the total mechanical energy of the object at:
i) Point A
ii) Point B
iii) Point C
iv) State the law which is verified by your calculations in parts (i), (ii), and (iii).A pulley system comprises two pulleys, one fixed and another movable.
i) Draw a labelled diagram of the arrangement and show clearly the directions of all the forces acting on it.
ii) What change can be made in the movable pulley of this system to increase the mechanical advantage of the system?i)
The arrangement of the pulley is as shown below. The forces acting on the arrangement is labeled accordingly. 
ii)
To increase the mechanical advantage of the system, reduce the friction between the string and the movable pulley.
i) The diagram alongside shows a ray of white light PQ coming from an object P and incident on the surface of a thick glass plane mirror. Copy the diagram and show the formation of three images of the object as formed by the mirror.
i) A person is tuning his radio set to a particular station. What is the person trying to do to tune it?
ii) Name the phenomenon involved, in tuning the radio set?
iii) Name the phenomenon named by you in part (ii).i) Draw a neat and labelled diagram to show the structure of an a.c. generator.
ii) State the energy conversion taking place in the generator when it is working.A nucleus 
emits an alpha particle followed by emission, therafter it emits two particles to form X3.
i) Copy and complete the values of A and Z for X3:
ii) Out of alpha, beta and gamma radiations:
1. Which radiation is the most penetrating?
2. Which radiations are negatively charged?
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