Ray Optics and Optical Instruments — Physics STD 12 Science — Question

If two soap bubbles of different radii are connected by a tube:

1. Air flows from bigger bubble to the smaller bubble till the sizes become equal.
2. Air flows from bigger bubble to the smaller bubble till the sizes are interchanged.
3. Air flows from the smaller bubble to the bigger.
4. There lis no flow of air.

The current in a coil changes from 4 ampere to zero in 0.1 s. If the average e.m.f. induced is 100 volt, what is the self inductance of the coil

(a) 2.5 H

(b) 25 H

(c) 400 H

(d) 40 H

The refractive index of the material of the prism and liquid are 1.56 and 1.32 respectively.  What will be the value of q for the following refraction

(a) sinθ  ≥

(b) sinθ ≥

(c) sinθ ≥

(d) sinθ ≥

The half-life of a radioactive substance against a-decay is 1.2 . What is the decay rate for 4  atoms of the substance

(a) 4.6	(b) 2.3
(c) 4.6	(d) 2.3

1 milli coulomb =

A hot liquid is kept in a big room. The logarithm of the numerical value of the temperature difference between the liquid and the room is plotted against time. The plot will be very nearly:

1. A straight line.
2. A circular are.
3. A parabola.
4. An ellipse.

A magnet freely suspended in a vibration magnetometer makes 10 oscillations per minute at a place A and 20 oscillations per minute at a place B. If the horizontal component of earth’s magnetic field at A is 36 ,  then its value at B is

(a) 36 × 10–6 T

(b) 72 × 10–6 T

(c) 144 × 10–6 T

(d) 288 × 10–6 T

The diffusion current in a p-n junction is:

1. From the n-side to the p-side.
2. From the p-side to the n-side.
3. From the n-side to the p-side if the junction is forward-biased and in the opposite direction if it is reverse-biased.
4. From the p-side to the n-side if the junction is forward-biased and in the opposite direction if it is reverse-biased.

Which one statement is correct ? A parallel plate air condenser is connected with a battery. Its charge, potential, electric field and energy are  and respectively. In order to fill the complete space between the plates a dielectric slab is inserted, the battery is still connected. Now the corresponding values Q, V, E  and U are in relation with the initially stated as 

(a) Q >

(b)

(c) V >

(d)

What is the use of a Van de Graff generator?