True/False: Modern Physics | JEE Advanced | 35 Years Chapter wise Previous Year Solved Papers for JEE PDF Download

True/False

Q.1. The kinetic energy of photoelectrons emitted by a photosensitive surface depends on the intensity of the incident  radiation.      (1981- 2 Marks)

Ans. F

Solution. For photoelectric effect 

hv – hv₀ = (K.E.)max 

where  h = Planck’s constt. 

v₀ = Threshold frequency 

⇒  (K.E.)_max ∝ n 

K.E. does not depend on the intensity of incident radiation.

Q.2. In a photoelectric emission process the maximum energy of the photo-electrons increases with increasing intensity of the incident light.        (1986 - 3 Marks)

Ans. F

Solution. (K.E.)_max = hv – hv₀ ⇒ (K.E.)_max ∝ v 

Thus maximum kinetic energy is proportional to frequency and not intensity.

Q.3. For a diode the variation of its anode current I_a with the anode voltage V_a at two different cathode temperatures T₁ and T₂  is shown in the figure. The temperature T₂  is greater than T₁.      (1986 - 3 Marks)

Ans. T

Solution. Note : When the cathode temperature is higher, then more number of electrons will be emitted which in turn will increase the anode current.

Q.4. The order of magnitude of the density of nuclear matter is 10⁴ kg m^–2.        (1989 - 2 Marks)

Ans. F

Solution.

where A = mass number.

Note : The order of nuclear density is 10¹⁷ kg/m³.