Science (English Medium) Class 12 - CBSE Important Questions for Physics

Two nuclei have mass numbers in the ratio 1: 2. What is the ratio of their nuclear densities?

A radioactive nucleus ‘A’ undergoes a series of decays according to the following scheme:

The mass number and atomic number of A are 180 and 72 respectively. What are these numbers for A₄?

The radioactive isotope D decays according to the sequence

If the mass number and atomic number of D₂ are 176 and 71 respectively, what is (i) the mass number (ii) atomic number of D?

Which property of nuclear force explains the constancy of binding energy per nucleon `((BE)/A)` for nuclei in the range 20< A < 170 ?

Define the term 'decay constant' of a radioactive sample. The rate of disintegration of a given radioactive nucleus is 10000 disintegrations/s and 5,000 disintegrations/s after 20 hr. and 30 hr. respectively from start. Calculate the half-life and the initial number of nuclei at t= 0. 

Write two distinguishing features of nuclear forces.

Complete the following nuclear reactions for α and β deca :

(i) `"_92^238U ->?  + _2^4He + Q`

(ii) `"_11^22Na ->?  + _10^22Ne + v`

Determine the distance of the closest approach when an alpha particle of kinetic energy 4.5 MeV strikes a nucleus of Z = 80, stops and reverses its direction.

The figure shows the plot of binding energy (BE) per nucleon as a function of mass number A. The letters A, B, C, D, and E represent the positions of typical nuclei on the curve. Point out, giving reasons, the two processes (in terms of A, B, C, D, and E ), one of which can occur due to nuclear fission and the other due to nuclear fusion.

Identify the nature of the radioactive radiations emitted in each step of the decay process given below.

`""_Z^A X -> _Z^A  _-1^-4 Y ->_Z^A  _-1^-4 W`

A radioactive substance disintegrates into two types of daughter nuclei, one type with disintegration constant λ₁ and the other type with disintegration constant λ₂ . Determine the half-life of the radioactive substance.

Answer the following question.
Draw the curve showing the variation of binding energy per nucleon with the mass number of nuclei. Using it explains the fusion of nuclei lying on the ascending part and fission of nuclei lying on the descending part of this curve.

James Chadwick, in 1932 studied the emission of neutral radiations when Beryllium nuclei were bombarded with alpha particles. He concluded that emitted radiations were neutrons and not photons. Explain.

Two nuclei may have the same radius, even though they contain different numbers of protons and neutrons. Explain.

The radius of \[\ce{^27_13X}\] nucleus is R. The radius of \[\ce{^125_53Y}\] nucleus will be ______.

Calculate the binding energy of an alpha particle in MeV. Given

mass of a proton = 1.007825 u

mass of a neutron = 1.008665 u

mass of He nucleus = 4.002800 u

1u = 931 MeV/c²

The following figure shows the input waveforms (A, B) and the output waveform (Y) of a gate. Identify the gate, write its truth table and draw its logic symbol.

Briefly explain how the output voltage/current is unidirectional.

What happens when a forward bias is applied to a p-n junction?

When is a transistor said to be in active state?