MODEL PAPER 4 — Physics STD 12 Science — Question

There are energy bands in a solid. Do we have really continuous energy variation in a band or do we have very closely spaced but still discrete energy levels?

Suppose the glass of the previous problem is covered by a jar and the air inside the jar is completely pumped out.

1. What will be the answers to the problem?
2. Show that the answers do not change if a glass of different shape is used provided the height, the bottom area and the volume are unchanged.

A parallel plate capacitor is charged by a battery. After some time the battery is disconnected and a dielectric slab of dielectric constant K is inserted between the plates. How would (i) the capacitance, (ii) the electric field between the plates and (iii) the energy stored in the capacitor, be affected? Justify your answer.

Draw a graph showing the variation of binding energy per nucleon with mass number for different nuclei. Explain, with the help of this graph, the release of energy by the process of nuclear fusion.

If the separation between the slits in a Young's double slit experiment is increased, what happens to the fringe-width? If the separation is increased too much, will the fringe pattern remain detectable?

A simple microscope has a magnifying power of 3.0 when the image is formed at the near point (25cm) of a normal eye.

1. What is its focal length?
2. What will be its magnifying power if the image is formed at infinity?

Name the parts of the electromagnetic spectrum which is:

1. Suitable for radar systems used in aircraft navigation.
2. Used to treat muscular strain.
3. Used as a diagnostic tool in medicine.

Write in brief, how these waves can be produced.

Comment on the following :(i) Electric conductivity.(ii) Dependence of resistivity and resistance on temperature.

radioactive isotope has a half-life of 5 years. After how much time is its activity reduced to 3.125% of its original activity?