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

The current in a long solenoid of radius R and having n turns per unit length is given by i= i₀ sin ωt. A coil having N turns is wound around it near the centre. Find (a) the induced emf in the coil and (b) the mutual inductance between the solenoid ant the coil.

A solenoid of length 20 cm, area of cross-section 4.0 cm² and having 4000 turns is placed inside another solenoid of 2000 turns having a cross-sectional area 8.0 cm² and  length 10 cm. Find the mutual inductance between the solenoids.

What is the difference between cathode rays and beta rays? When the two are travelling in space, can you make out which is the cathode ray and which is the beta ray?

In beta decay, an electron (or a positron) is emitted by a nucleus. Does the remaining atom get oppositely charged?

During a negative beta decay,

Ten grams of ⁵⁷Co kept in an open container beta-decays with a half-life of 270 days. The weight of the material inside the container after 540 days will be very nearly

As the speed of a particle increases, its rest mass _______________ .

Consider a sample of a pure beta-active material.

A uniform magnetic field B exist in a region. An electron projected perpendicular to the field goes in a circle. Assuming Bohr's quantization rule for angular momentum, calculate (a) the smallest possible radius of the electron (b) the radius of the nth orbit and (c) the minimum possible speed of the electron.

A free neutron beta-decays to a proton with a half-life of 14 minutes. (a) What is the decay constant? (b) Find the energy liberated in the process.

(Use Mass of proton m_p = 1.007276 u, Mass of `""_1^1"H"` atom = 1.007825 u, Mass of neutron m_n = 1.008665 u, Mass of electron = 0.0005486 u ≈ 511 keV/c²,1 u = 931 MeV/c².)

Complete the following decay schemes.

(a) `"" _88^226Ra → alpha+`

(b) `""_8^19O → _9^19F+`

(c) `""_13^25Al → ""_12^25Mg+`

A plate current of 10 mA is obtained when 60 volts are applied across a diode tube. Assuming the Langmuir-Child relation \[i_p  \infty  V_p^{3/2}\] to hold, find the dynamic resistance r_p in this operating condition.

The plate current in a diode is 20 mA when the plate voltage is 50 V or 60 V. What will be the current if the plate voltage is 70 V?

The power delivered in the plate circular of a diode is 1.0 W when the plate voltage is 36 V. Find the power delivered if the plate voltage is increased to 49 V. Assume Langmuir-Child equation to hold.

A triode value operates at V_p = 225 V and V_g = −0.5 V.
The plate current remains unchanged if the plate voltage is increased to 250 V and the grid voltage is decreased to −2.5 V. Calculate the amplification factor.

The dynamic plate resistance of a triode value is 10 kΩ. Find the change in the plate current if the plate voltage is changed from 200 V to 220 V.

Find the values of r_p, µ and g_m of a triode operating at plate voltage 200 V and grid voltage −6. The plate characteristics are shown in the figure.

The gain factor of an amplifier in increased from 10 to 12 as the load resistance is changed from 4 kΩ to 8 kΩ. Calculate (a) the amplification factor and (b) the plate resistance.

Use Einstein’s photoelectric equation to show how from this graph, 
(i) Threshold frequency, and (ii) Planck’s constant can be determined.

How does one explain the emission of electrons from a photosensitive surface with the help of Einstein’s photoelectric equation?