Electrostatic Potential and Capacitance — Physics STD 12 Science — Question

When semiconductor is doped half with trivalent and half with pentavalent impurities, junction formed is known as:

When a beam of accelerated electrons hits a target, a continuous X-ray spectrum is emitted from the target. Which of the following wavelength is absent in the X-ray spectrum, if the X-ray tube is operating at 40,000 volts

(a) 0.25 Å

(b) 0.5 Å

(c) 1.5 Å

(d) 1.0 Å

A heater coil connected to a supply of a 220 V is dissipating some power  The coil is cut into half and the two halves are connected in parallel. The heater now dissipates a power  The ratio of power  is

(a) 2 : 1

(b) 1 : 2

(c) 1 : 4

(d) 4 : 1

The time constant of an LR circuit represents the time in which the current in the circuit

(a) Reaches a value equal to about 37% of its final value

(b) Reaches a value equal to about 63% of its final value

(c) Attains a constant value

(d) Attains 50% of the constant value

The optical fibre works on the principle of :

When air is replaced by a dielectric medium of constant k, the maximum force of attraction between two charges separated by a distance

(a) Decreases k  times	(b) Remains unchanged
(c) Increases k times	(d) Increases  times

The energy of the highest energy photon of Balmer series of hydrogen spectrum is close to

(a) 13.6 eV

(b) 3.4 eV

(c) 1.5 eV

(d) 0.85 eV

With the decrease in the wave length of the incident radiation the velocity of the photoelectrons emitted from a given metal

The phase difference between current and voltage in an A.C. circuit containing capacitance only is :

The capacitance of a metallic sphere will be 1μF, if its radius is nearly

(a) 9 km

(b) 10 m

(c) 1.11 m

(d) 1.11 cm