Science (English Medium) कक्षा १२ - CBSE Question Bank Solutions for Physics

The saturation current in a triode valve can be changed by changing _____________ .

The plate current in a diode is zero. It is possible that _____________ .

(a) the plate voltage is zero
(b) the plate voltage is slightly negative
(c) the plate voltage is slightly positive
(d) the temperature of the filament is low

The plate current in a triode valve is zero. The temperature of the filament is high. It is possible that ____________ .

(a) V_g > 0, V_p > 0
(b) V_g > 0, V_p < 0
(c) V_g < 0, V_p > 0
(d) V_g < 0, V_p < 0

A discharge tube contains helium at low pressure. A large potential difference is applied across the tube. Consider a helium atom that has just been ionised due to the detachment of an atomic electron. Find the ratio of the distance travelled by the free electron to that by the positive ion in a short time dt after ionisation.

A molecule of a gas, filled in a discharge tube, gets ionised when an electron is detached from it. An electric field of 5.0 kV m⁻¹ exists in the vicinity of the event. (a) Find the distance travelled by the free electron in 1 µs, assuming there's no collision. (b) If the mean free path of the electron is 1.0 mm, estimate the time of transit of the free electron between successive collisions.

The mean free path of electrons in a gas in a discharge tube is inversely proportional to the pressure inside it. The Crookes dark space occupies half the length of the discharge tube when the pressure is 0.02 mm of mercury. Estimate the pressure at which the dark space will fill the whole tube.

Two discharge tubes have identical material structures and the same gas is filled in them. The length of one tube is 10 cm and that of the other tube is 20 cm. Sparking starts in both the tubes when the potential difference between the cathode and the anode is 100 V. If the pressure in the shorter tube is 1.0 mm of mercury, what is the pressure in the longer tube?

The saturation current from a thoriated-tungsten cathode at 2000 K is 100 mA. What will be the saturation current for a pure-tungsten cathode of the same surface area operating at the same temperature? The constant A in the Richardson-Dushman equation is 60 × 10⁴ Am ⁻² K⁻² for pure tungsten and 3.0 × 10⁴ Am ⁻² k⁻² for thoriated tungsten. The work function of pure tungsten is 4.5 eV and that of thoriated tungsten is 2.6 eV.

The plate current in a triode can be written as \[i_p  = k \left( V_g + \frac{V_p}{\mu} \right)^{3/2}\] Show that the mutual conductance is proportional to the cube root of the plate current.

An a-particle and a proton of the same kinetic energy are in turn allowed to pass through a magnetic field `vec"B"`, acting normal to the direction of motion of the particles. Calculate the ratio of radii of the circular paths described by them.

Differentiate between amplitude modulated (AM) and frequency modulated (FM) waves by drawing suitable diagrams. Why is FM signal preferred over AM signal?

A 100 Ω resistor is connected to a 220 V, 50 Hz ac supply.

1. What is the rms value of current in the circuit?
2. What is the net power consumed over a full cycle?

A 100 Ω resistor is connected to a 220 V, 50 Hz ac supply.

What is the net power consumed over a full cycle?

Find the Q-value and the kinetic energy of the emitted α-particle in the α-decay of `""_86^220"Rn"`.

Given `"m"(""_88^226"Ra")` = 226.02540 u, `"m"(""_86^222 "Rn")` = 222.01750 u, 

`"m"(""_86^220 "Rn")`= 220.01137 u, `"m"(""_84^216 "Po")`= 216.00189 u.

Effective voltage V_rms is related to peak voltage V_o by ______.

If V_m and I_m are peak voltage and current, impedance Z in an AC circuit is ______.

Atomic mass unit (u) is defined as ________ of the mass of the carbon (¹²C) atom.

Nuclear species or nuclides are shown by the notation ________ where X is the chemical symbol of the species.

\[\ce{^197_79Au}\] contains ______.

The nuclei of isotopes of a given element contain the same number of ______.