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

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.

Define one tesla using the expression for the magnetic force acting on a particle of charge q moving with velocity \[\vec{v}\]  in a magnetic field \[\vec{B}\] .

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.

A circular coil of N turns and radius R carries a current I. It is unwound and rewound to make another coil of radius R/2, current I remaining the same. Calculate the ratio of the magnetic moments of the new coil and original coil.

A particle of charge ‘q’ and mass ‘m’ is moving with velocity .`vecV` It is subjected to a uniform magnetic field `vecB` directed perpendicular to its velocity. Show that it describes a circular path. Write the expression for its radius.

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

A steady current (I₁) flows through a long straight wire. Another wire carrying steady current (I₂) in the same direction is kept close and parallel to the first wire. Show with the help of a diagram how the magnetic field due to the current I₁ exerts a magnetic force on the second wire. Write the expression for this force.

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.

Two charges −q and +q are located at points A (0, 0, −a) and B (0, 0, +a) respectively. How much work is done in moving a test charge from point P (7, 0, 0) to Q (−3, 0, 0)?

A charge ‘q’ moving along the X- axis with a velocity  `vecv` is subjected to a uniform magnetic field B along the Z-axis as it crosses the origin O.

(i) Trace its trajectory.

(ii) Does the charge gain kinetic energy as it enters the magnetic field? Justify your answer.

In motor vehicles, a convex mirror is attached near the driver's seat to give him the view of the traffic behind. What is the special function of this convex mirror which a plane mirror can not do?

If an object far away from a convex mirror moves towards the mirror, the image also moves. Does it move faster, slower or at the same speed as compared to the object?

Can mirrors give rise to chromatic aberration?