NEET Modern Physics MCQs & PYQs

Practice NEET Modern Physics Questions

Question 241:

easy

When light of wavelength $300 nm$ (nanometer) falls on a photoelectric emitter, photoelectrons are liberated. For another emitter, however, light of $600 nm$ wavelength is sufficient for creating photoemission. What is the ratio of the work functions of the two emitters?

(1993)

The work function is inversely proportional to the threshold wavelength: $\phi = \frac{hc}{\lambda_0}$. The ratio of the work functions is $\frac{\phi_1}{\phi_2} = \frac{\lambda_{02}}{\lambda_{01}} = \frac{600 nm}{300 nm} = \frac{2}{1}$. Thus, the ratio is 2 : 1.

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Question 242:

easy

Number of ejected photoelectrons increases with increase

(1993)

The number of photoelectrons ejected per second from a photosensitive surface is directly proportional to the intensity of the incident light, assuming the frequency is above the threshold.

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Question 243:

easy

51. The cathode of a photoelectric cell is changed such that the work function changes from $W_1$ to $W_2$ ($W_2 > W_1$). If the current before and after changes are $I_1$ and $I_2$, all other conditions remaining unchanged, then (assuming $h\nu > W_2$) (1992)

Saturation photoelectric current depends only on the intensity of the incident light (number of photons per second) and is independent of the work function of the cathode material, provided the incident frequency is above the threshold. Therefore, $I_1 = I_2$.

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Question 244:

easy

If the kinetic energy of the particle is increased to 16 times its previous value, the percentage change in the de-Broglie wavelength of the particle is

(2014)

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Question 245:

easy

The wavelength $\lambda_e$ of an electron and $\lambda_p$ of a photon of same energy E are related by:

(2013)

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Question 246:

easy

An $\alpha$-particle moves in a circular path of radius 0.83 cm in the presence of a magnetic field of $0.25 Wb/m^2$. The de Broglie wavelength associated with the particle will be:

(2012 Pre)

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Question 247:

easy

Electrons used in a electron microscope are accelerated by a voltage of 25 kV. If the voltage is increased to 100 kV then the de Broglie wavelength associated with the electrons would:

(2011 Pre)

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Question 248:

easy

A radioactive nucleus of mass M emits a photon of frequency $\nu$ and the nucleus recoils. The recoil energy will be:

(2011 Pre)

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Question 249:

easy

A particle of mass 1 mg has the same wavelength as an electron moving with a velocity of $3 \times 10^6 ms^{-1}$. The velocity of the particle is (mass of electron = $9.1 \times 10^{-31} kg$):

(2008)

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Question 250:

easy

If particles are moving with same velocity, then de-Broglie wavelength is maximum for:

(2002)

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