When paper is tightly rolled around an iron bar and then placed in a flame, the paper does not catch fire. Explain.

When a wire is wound around a soft iron bar, and a current is passed through it, the soft iron bar behaves like a magnet.

When acoustic resonance takes place, a loud sound is heard. Why does this happen ? Explain.

(a) When a moist blue litmus paper is dipped in a solution of hypochlorous acid, it first turns red and then latter gets decolourised. Explain. (b) Iodine is liberated when KI is added to a solution of Cu^(2+) ions but Cl_(2) is not liberated when KCl is added to a solution of Cu^(2+) ions. why?

A salt, when warmed with zinc powder and an NaOH solution, gives a gas that turns a filter paper soaked with an alkaline solution of K_(2)[HgI_(4)] brown. The salt responds to the brown ring test when acetic acid is used in place of sulphuric acid. The anion present in the salt is:

(a) Define a wavefront. Using Huygen's principle, verify the laws of reflection at a plane surface . (b) In a single slit diffraction experiment the wildth of the slit is made double the orignal width. How does this affect the size and intensity of the central diffraction band ? Explain. (c) When a tiny circular obstacle in placed in the path of light from a distance source, a bright spot is seen at the centre of the obstacle . Explain why.

When a charged comb is brought near a small piece of paper, it attracts the piece. Does the paper, it attracts the piece. Does the paper become charged when the conb is brought near it ?

The diagram shows a coil wound around a U shape soft iron bar AB. What is the polarity induced at the ends A and B when the switch is pressed ?

The diagram shows a coil wound around a U shape soft iron bar AB. What is the polarity induced at the ends A and B when the switch is pressed ?

Explain why iron filings which are sprinkled on a sheet of cardboard placed over a bar magnet, take up a definite pattern when cardboard is slightly tapped.

A wire is placed between the poles of twofixed bar magnets as shown in the figure. A small current in the wire is into the plane of the paper. The direction of the magnetic force on the wire is