Test: JEE Main 35 Year PYQs- Modern Physics - JEE MCQ

KEY CONCEPT : The energy of  nth orbit of hydrogen is given by

Therefore the energy required to remove electron from n = 2 is + 3.4 eV.

Pure silicon, at absolute zer o, will contain al l the electrons in bounded state. The conduction band will be empty. So there will be no free electrons (in conduction band) and holes (in valence band) due to thermal agitation. Pure silicon will act as insulator.

Charged particles are deflected in magnetic field.

We know that work function is the energy required and energy E = hu

For mation of covalent bond is best explain ed by molecular orbital theory.

After every half-life, the mass of the substance reduces to half its initial value.

Specific resistance is resistivity which is given by

where n  = no. of free electrons per unit volume and τ  = average relaxation time For a conductor with  rise in temperature n increases and τ decreases. But decrease in t is more dominant than increase in n resulting an increase in the value of ρ.
For a semiconductor with rise in temperature, n increases and τ decreases. But the increase in n is more dominant than decrease in τ resulting in a decrease in the value of ρ.

The energy band gap is maximum in insulators.

Emitter sends the majority charge carrriers towards the collector. Therefore emitter is most heavily doped.

β -rays are fast moving beam of electrons.

The resist ance of metal (like Cu) decr eases with decrease in temperature whereas the resistance of a semi-conductor (like Ge) increases with decrease in temperature.

The electromagnetic spectrum is as follows

∴ γ-rays has least wavelength

(c) : Linear momentum is conserved

When the temperature increases, certain boun ded electrons become free which tend to promote conductivity. Simultaneously  number of collisions between electrons and positive kernels increases

The number of  α - particles released = 8 Therefore the atomic number should decrease by 16
The number of β^- -particles released = 4
Therefore the atomic number should increase by 4.
Also the number of β⁺ particles released is 2, which should decrease the atomic number by 2.
Therefore the final atomic number is
92 –16 + 4 – 2 = 78

For one photocathode

For another photo cathode

Subtracting (ii) from (i) we get

The radioactive substances emit α -particles (Helium nucleus), β – particles (electrons) and neutrinoes.

The average kinetic energy per molecule 

This kinetic energy should be able to provide the repulsive potential energy

The ionisation potential increases from left to right in a period and decreases from top to bottom in a group.
Therefore ceasium will have the lowest ionisation potential.

The wavelength of spectrum is given by

where m = mass of electron
M = mass of nucleus.
For different M, R is different and therefore λ is different

As in reverse bias, the current through the 0000 is zero through the electric field is also zero.

For lithium ion  Z = 3  ; n = 2  (for first excited state)

Momentum of photon = E/c

Change in momentum = 2E/c

= momentum transferred to the surface(the photon will reflect with same magnitude of momentum in opposite direction)

From E quation K .E = hv-φ
slope of graph of  K.E  & v is h (Plank's constant) which is same for all metals

For the longest wavelength to emit photo electron

From conservation of momentum m₁v₁ = m₂v₂

The nuclear reaction of  process is  He Energy released  = 4 × (7) – 4(1.1) = 23.6 MeV

KEY CONCEPT :

Distance of closest approach

Electrons move from base to emmitter.