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

In the following common emitter configuration an NPN transistor with current gain b = 100 is used. The output voltage of the amplifier will be

(a) 10 mV

(b) 0.1 V

(c) 1.0 V

(d) 10 V

Two electric dipoles of moment P and 64 P are placed in opposite direction on a line at a distance of 25 cm. The electric field will be zero at point between the dipoles whose distance from the dipole of moment P is

(a) 5 cm

(b)   cm

(c) 10 cm

(d)  cm

The band spectra (characteristic of molecular species) is due to emission of radiation

(a) Gaseous state

(b) Liquid state

(c) Solid state

(d) All of three states

The X – 1/T graph for an alloy of paramagnetic nature is shown in Fig. The curie constant is, then

(a) 57 K

(b) 2.8

(c) 570 K

(d) 17.5

The plate resistance of a triode is 2.5 × 10⁴ W and mutual conductance is 2 × 10^–3 mho. What will be the value of amplification factor

(a) 50

(b) 1.25 × 107

(c) 75

(d) 2.25 × 107

In insulator:

Assertion  :   The tyres of aircraft's are slightly conducting.

Reason      : If a conductor is connected to ground, the extra charge induced on conductor will flow to ground.

(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 half-life period of radium is 1600 years. Its average life time will be

(a) 3200 years

(b) 4800 years

(c) 2319 years

(d) 4217 years

A hollow insulated conducting sphere is given a positive charge of 10μC. What will be the electric field at the centre of the sphere if its radius is 2 meters

(a) Zero

(b) 5

(c) 20

(d) 8

The conductivity of a semiconductor increases with increase in temperature because: