Wave Optics — Physics STD 12 Science — Question

Figure shows a siphon. The liquid shown is water. The pressure difference P_a P_A between the points A and B is the reading will be:

1. 400 Nm⁻²
2. 3000 Nm⁻²
3. 1000 Nm⁻²
4. zero.

In a common emitter transistor, the current gain is 80. What is the change in collector current, when the change in base current is 250 mA

(a) 80  × 250 mA

(b) (250 – 80) mA

(c) (250 + 80) mA

(d) 250/80 mA

An electron moving with a speed u along the positive x-axis at y = 0 enters a region of uniform magnetic field   which exists to the right of y-axis. The electron exits from the region after some time with the speed v at co-ordinate y, then

(a) v > u, y < 0

(b) v = u, y > 0

(c) v > u, y > 0

(d) v = u, y < 0

A 100 W bulb B₁, and two 60-W bulbs B₂ and B₃, are connected to a 250 V source, as shown in the figure. Now W₁, W₂ and W₃ are the output powers of the bulbs B₁, B₂ and B₃, respectively. Then

(a)

(b)

(c)

(d)

Assertion  :   The presence of water molecules makes separation of ions easier in electrolyte.  

Reason    : The presence of water molecules in electrolyte decreases the resistance of electrolyte.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

The resistance of 10 metre long potentiometer wire is 1ohm/meter. A cell of e.m.f. 2.2 volts and a high resistance box are connected in series to this wire. The value of resistance taken from resistance box for getting potential gradient of 2.2 millivolt/metre will be

(a) 790 Ω

(b) 810 Ω

(c) 990 Ω

(d) 1000 Ω

Three semi-conductors are arranged in the increasing order of their energy gap as follows. The correct  arrangement is

(a) Tellurium, germanium, silicon	(b) Tellurium, silicon, germanium
(c) Silicon, germanium, tellurium	(d) Silicon, tellurium, germanium

In the figure a potential of + 1200 V is given to point A and point B is earthed, what is the potential at the point P

(a) 100 V

(b) 200 V

(c) 400 V

(d) 600 V

What is the effect on Fresnel’s biprism experiment when the use of white light is made

(a) Fringe are affected

(b) Diffraction pattern is spread more

(c) Central fringe is white and all are coloured

(d) None of these

The color coding of  earth, live and neutral wire respectively is: