Science (English Medium) Class 12 - CBSE Question Bank Solutions

State whether the following statement are true or false: 

A motor works on the principle electric generator? 

When a wire is moved up and down in a magnetic field, a current is induced in the wire. What is this phenomenon known as?

When current is 'switched on' and 'switched off' in a coil, a current is induced in another coil kept near it. What is this phenomenon known as?

 Describe different ways to induce current in a coil of wire.

An induced current is produced when a magnet is moved into a coil. The magnitude of induced current does not depend on:  

(a) the speed with which the magnet is moved
(b) the number of turns of the coil
(c) the resistivity of the wire of the coil
(d) the strength of the magnet

When the magnet shown in the diagram below is moving towards the coil, the galvanometer gives a reading to the right. 

() What is the name of the effect being produced by the moving magnet?
(2) State what happens to the reading shown on the galvanometer when the magnet is moving away from the coil.
(3) The original experiment is repeated. This time the magnet is moved towards the coil at a great speed. State two changes you would notice in the reading on the galvanometer.

Name the em waves which are used for the treatment of certain forms of cancer. Write their frequency range ?

Name the em waves which are produced during radioactive decay of a nucleus. Write their frequency range ?

Welders wear special glass goggles while working. Why? Explain.

When Puja, a student of 10^th class, watched her mother washing clothes in the open, she observed coloured soap bubbles and was curious to know why the soap bubbles appear coloured. In the evening when her father, an engineer by profession, came home, she asked him this question. Her father explained to her the basic phenomenon of physics due to which the soap bubbles appear coloured.
(a) What according to you are the values displayed by Puja and her father?
(b) State the phenomenon of light involved in the formation of coloured soap bubbles.

Welders wear special goggles or face masks with glass windows to protect their eyes from electromagnetic radiations. Name the radiations and write the range of their frequency.

A light metal disc on the top of an electromagnet is thrown up as the current is switched on. Why? Give reason.

Draw a plot showing the variation of (i) electric field (E) and (ii) electric potential (V) with distance r due to a point charge Q.

Show that the density of nucleus over a wide range of nuclei is constant-independent of mass number A.

State clearly how photoelectric equation is obtained using the photon pictu.re of electromagnetic radiation.

Write the three salient features observed in photoelectric effect which can be explained using this equation.

Define the term ‘stopping potential’ in relation to photo-electric effect.

Show diagrammatically how an alternating emf is generated by a loop of wire rotating in a magnetic field. Write the expression for the instantaneous value of the emf induced in the rotating loop.

Two nuclei have mass numbers in the ratio 1: 2. What is the ratio of their nuclear densities?

Can two equi-potential surfaces intersect each other? Give reasons.