Moving Charges and Magnetism — Physics STD 12 Science — Question

With a change of load resistance of a triode, used as an amplifier, from 50 kilo ohms to 100 kilo ohms, its voltage amplification changes from 25 to 30. Plate resistance of the triode is

(a) 25 kW

(b) 75 kW

(c) 7.5 kW

(d) 2.5 kW

Time period of oscillation of a magnetic needle is

The SI unit of resistivity is:

A capacitor is fully charged with a battery. Then the battery is removed and coil is connected with the capacitor in parallel, current varies as

(a) Increases monotonically	(b) Decreases monotonically
(c) Zero	(d) Oscillates indefinitely

When an ammeter is shunted, its measuring range :

The ratio of radii of nuclei   and   is 3 : 5. The number of neutrons in the nuclei of X will be

(a) 52

(b) 73

(c) 125

(d) 13

The dielectric constant of water is :

The characteristic X-ray radiation is emitted, when

(a) The electrons are accelerated to a fixed energy

(b) The source of electrons emits a monoenergetic beam

(c) The bombarding electrons knock out electrons from  the inner shell of the target atoms and one of the outer electrons falls into this vacancy

(d) The valence electrons in the target atoms are removed as a result of the collision

The junction diode in the following circuit requires a minimum current of 1 mA to be above the knee point (0.7 V) of its I-V characteristic curve. The voltage across the diode is independent of current above the knee point. If V_B  = 5V, then the maximum value of R so that the voltage is above the knee point, will be

(a) 4.3 kW

(b) 860 kW

(c) 4.3 W

(d) 860 W

The continuous X-rays spectrum produced by an X-ray machine at constant voltage has

(a) A maximum wavelength	(b) A minimum wavelength
(c) A single wavelength	(d) A minimum frequency