Atoms — Physics STD 12 Science — Question

Electric flux over a surface in an electric field may be:

A steady current is passing through a linear conductor of non uniform cross-section. The net quantity of charge crossing any cross section per second is:

In a transistor, a change of 8.0 mA in the emitter current produces a change of 7.8 mA in the collector current. What change in the base current is necessary to produce the same change in the collector current

(a) 50 mA

(b) 100 mA

(c) 150 mA

(d) 200 mA

The wavelength 21 cm emitted by atomic hydrogen in interstellar space belongs to

(a) Radio waves

(b) Infrared waves

(c) Microwaves

(d) g-rays

Which one is not the property of charge?

A sinusoidal voltage of peak value 200 volt is connected to a diode and resistor R in the circuit shown so that half wave rectification occurs. If the forward resistance of the diode is negligible compared to R the rms voltage (in volt) across R is approximately

(a) 200

(b) 100

(c)

(d) 280

Atomic power station at Tarapore has a generating capacity of 200 MW. The energy generated in a day by this station is

(a) 200 MW

(b) 200 J

(c) 4800  J

(d) 1728  J

What is the suitable material for electric fuse?

The half-life of radioactive Polonium (Po) is 138.6 days. For ten lakh Polonium atoms, the number of disintegrations in 24 hours is

(a) 2000

(b) 3000

(c) 4000

(d) 5000