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401.

If the de-Broglie wavelength of a proton is `10^(-13)` m, the electric potentia through which it must have been accelerated isA. `4.07xx10^4 V`B. `8.15xx10^4 V`C. `8.15xx10^3 V`D. `4.07xx10^5 V`

Answer» Correct Answer - B
`:. lambda = (h)/(sqrt2qvm)`
`V = (h^2)/(2qmlambda^2)`
Discussion
402.

A proton and an alpha - particle are accelerated through same potential difference. Then, the ratio of de-Broglie wavelength of proton and alpha-particle isA. `sqrt2`B. `(1)/(sqrt2)`C. `2sqrt2`D. None of these

Answer» Correct Answer - C
`:. lambda = (h)/(sqrt2qvm) or lambda prop (1)/(sqrtqm)`
`:. (lambda_p)/(lambda_(alpha)) =(sqrtqm)_(alpha)/(sqrtqm)_p =sqrt(2xx4)/sqrt(1xx1) = 2sqrt2`
Discussion
403.

Half-life of a radioactive substance `A` is two times the half-life of another radioactive substance `B`. Initially, the number of `A` and `B` are `N_(A)` and `N_(B)`, respectively . After three half-lives of `A`, number of nuclei of both are equal. Then, the ratio `N_(A)//N_(B)` is .A. `1//4`B. `1//8`C. `1//3`D. `1//6`

Answer» Correct Answer - B
Discussion
404.

Hydrogen gas in the atomic state is excited to an energy level such tht the electrostatic potential energy of H-atom becomes `-1.7 eV`. Now, a photoelectric plate having work function w=2.3 eV is exposed to the emission spectra of this gas. Assuming all the transitions to be possible, find the minimum de-Broglie wavelength of the ejected photoelectrons.

Answer» Correct Answer - C
`U = - 1.7 eV`
`:. E = (U)/(2) =- 0.85 eV = (-13.6)/(n^2)`
`:. N =4 ` Ejected photoelectron will have minimum
de-Broglie wavelength corresponding to transition
from n = 4 to n=1.
`Delta E = E_4 -E_1 =- 0.85 - (-13.6)`
= 12.75 eV
`K_(max) = DeltaE - W = 10.45 eV`
`:. lambda = sqrt((150)/(10.45)) Å` (for an electron)`
= 3.8 Å
Discussion
405.

A radioactive source in the form of a metal sphere of diameter 3.2×10^−3m emits β-particle at a constant rate of 6.25×10^10particle/sec. The source is electrically insulated and all the β-particle are emitted from the surface. The potential of the sphere will rise to 1 V in timeA. `180 mus`B. `90 mus`C. `18mus`D. `9mus`

Answer» Correct Answer - C
Discussion
406.

An electron and a proton are seperated by a large distance and the electorn approaches the proton with a kinectic energy of 2 eV. If the electron is captured by the proton to form a hydrogen atom in the ground state, what wavelength photon would be given off?

Answer» Correct Answer - C
Energy of electron in ground state of hydrogen
atom is -13.6 eV. Earlier it had a kinetic energy of 2 eV. Therefore, energy of
photon released durig
formation of hydrogen atom,
`DeltaE = 2 - (-13.6) = 15.6 eV`
`:gt lambda = (12375)/(DeltaE) = (12375)/(15.6)`
=793.3 Å`
Discussion
407.

An electron and a proton are separated by a large distance and the electron approaches the proton with a kinetic energy of 2 eV. If the electron is captured by the proton to form a hydrogen atom in the ground state, what wavelength photon would be given off?A. `1262.2 Å`B. `793.3 Å`C. `1204.6 Å`D. `942.6 Å`

Answer» Correct Answer - B
Discussion
408.

An electron and a proton are separated by a large distance and the electron approaches the proton with a kinetic energy of 2 eV. If the electron is captured by the proton to form a hydrogen atom in the ground state, what wavelength photon would be given off?A. `2.4 eV`B. `2.7 eV`C. `2.9 eV`D. `5.4 eV`

Answer» Correct Answer - B
Discussion
409.

The frequencies of electromagnetic waves employed in space communication lie in the range of -A. `10^(4) Hz " to " 10^(7) Hz`B. `10^(4) Hz " to " 10^(11) Hz`C. `1 Hz " to " Hz`D. `1 Hz " to " 10^(11) Hz`

Answer» Correct Answer - B
Discussion
410.

Two identical p=- a junctions may be connected in seres in which a bettery in three ways , fig . The potential drops access the two p - n junction are equal in A. circuit `1` and circuit`2`B. circuit `2` and circuit`3`C. circuit `3` and circuit`1`D. circuit `1` only

Answer» Correct Answer - B
Since and Alaminium are trivalent are in series , therefore the potential drop acros , be propotional will be equal , the potaltial will equal its circuit I , the two p -n junction are atteched such that the one is biased (low resistant) and after is reverse biased (high resistence ) whererase in the ather two circuit both are forward biased or reversed biased
Discussion
411.

which of the following are not electromagnetic waves ?A. cosmic raysB. `Gamma rays`C. `beta- rays`D. X- rays

Answer» Correct Answer - C
`beta - rays` are fast moving beam of electrons
Discussion
412.

a p -n juction (D) shown in the figure can act an a rectifier An alternatting current source (V) is connected in the circuit The corrent (I ) in the resistor® can be shown by :A. B. C. D.

Answer» Correct Answer - B
We know that a single p -n diade connected to an a- c souece acts as a wave rectifier [ forward biased in one half cycle and reverse biased in the other half cycle ]
Discussion
413.

In the forward blas arrangement of a `p-n` junction rectifier , the `p` and is connected to the ….. Terminal of the bettery and the direction of the currect is from …… to …. In the reclifier .

Answer» Correct Answer - A
Positive , `p- part , n- part
Discussion
414.

The part of a transistor which is most heavily doped to product large number of majority carriers isA. emmiterB. baseC. collectorD. can be any of the above three

Answer» Correct Answer - A
Emitted sands majority charge carriers toward the collector . Therefore is most heavily doped
Discussion
415.

A full - wave rectifier circult along the out - put is shown in figure . The contribution (s) from the diode `1` is are .` A. `C`B. `A,C`C. `B,D`D. `A,B,C,D`

Answer» Correct Answer - B
As shown in the fig (i) during one half cycle the reversed biased and bence non conducting.
`(# JMA_MP_C17_037_S01.png" width="80%">
During the ofter half cycle, diode (i) gets forward biased and is conducting . Thus diode (1) conduct in the ofter so the correct option is (b) (a and c)
Discussion
416.

The energy band gap is maximum inA. metalsB. superoonductorsC. insulatorsD. semiconductors

Answer» Correct Answer - C
The energy band gap is maximum in insulators
Discussion
417.

The probbility of electrons to be found in the conduction band of an intrinsit semiconductor at a finile temperatureA. increase exponenially with increases band gapB. decreases exponenially with increases band gapC. decreases with increases temperatureD. is independent of the temperature and the band gap

Answer» Correct Answer - B
KEY CONCEPT: For a semi condactor `n = n_(0)e^(bar Eg//kT)` where `n_(0) = no ` of free electrons at absolute zero `n = no` of free electron at T kelvin, E_(g)= Energy gap , k = Boizmana constant` .
As E_(g) ` increase , `n` decrease exponentially.
Discussion
418.

By increasing the temperature , the specific of a conductor and a semiconductorA. increases for bothB. decrases for bothC. increases, decreasesD. decreases , increases

Answer» Correct Answer - C
Specific resistance is resistively which is given by
`p = (m)/(ne^(2) tau) `
where `n = no` , of free electron per unit valume
and `tau = `average relacation time
for a conducter with rise in temperatute and `tau `decreases But decreases in `tau` is more dominant than increase in `n` resulting an increase in the value of p
for a semiconducter with rise in temperatute and `tau `increases and `tau` decreases but the increases i `n` more dominant than decrease in `tau` resulting an decrease is the value of p
Discussion
419.

If `N_(0)` is the original mass of the substance of half - life period `t_(1//2) = 5 year` then the amount of substance left after `15` year isA. `N_(0)//8`B. `N_(0)//16`C. `N_(0)//2`D. `N_(0)//4`

Answer» Correct Answer - A
After every half - life , the mass of the substance reduces to half its initial value
`N_(0) overset(5year)rarr N_(0)/(2) overset(5 years)rarrN_(0)/(2^(2)) overset(5 years)rarrN_(0)/(8)`
Discussion