Pathak's Academy Spectrum
Topics:Modern Physics
1. Dual nature of particle 2. Structure of atom and nuclei 3. Semiconductor devices
Marks: 30 Time: 1h 10 min
Section - A
Q.No. 1 : Select and write the correct answer (any 6) [06]
i) A photocell is used to automatically switch on the street lights in the evening
when the sunlight is low in intensity. Thus it has to work with visible light. The
material of the cathode of the photocell is
(A) zinc (B) aluminum
(C) nickel (D) potassium
ii) An electron, a proton, an α-particle and a hydrogen atom are moving with the same
kinetic energy. The associated de Broglie wavelength will be longest for
(A) electron (B) proton
(C) α-particle (D) hydrogen atom
iii) In which of the following systems will the radius of the first orbit of the electron
be smallest?
(A) hydrogen (B) singly ionized helium
(C) deuteron (D) tritium
iv) The radius of the 4th orbit of the electron will be smaller than its 8th orbit by a
factor of
(A) 2 (B) 4
(C) 8 (D) 16
v) In a BJT, largest current flow occurs
(A) in the emitter
(B) in the collector
(C) in the base
(D) through CB junction
vi) Solar cell operates on the principle of:
(A) diffusion
(B) recombination
(C) photovoltaic action
(D) carrier flow
vii) A logic gate is an electronic circuit which:
(A) makes logical decisions
(B) allows electron flow only in one
direction
(C) works using binary algebra
(D) alternates between 0 and 1 value
Q. 2 Answer the following. [04]
i) State any two postulates of Bohr’s atomic model.
ii) On which factors does the wavelength of light emitted by a LED depends?
iii) Write the Boolean expression for (i) OR gate, (ii) AND gate
iv) What is photoelectric effect?
Section - B
Attempt any Four. [5 x 2 = 10 M]
i) Explain what you understand by the de Broglie wavelength of an electron.
ii) State the principle and any two uses of a solar Cell.
iii) What do you understand by the term wave-particle duality?
iv) Draw the diagram of hydrogen spectrum.
v) Explain the forward and the reverse characteristic of a pn junction diode.
vi) Draw the circuit diagram for common Emitter amplifier using npn transistor.
Section - C
Attempt any Two. [3 x 2 = 6 M]
i) Draw the circuit diagram of a half wave rectifier. Explain its working. What is the frequency of ripple in its output?
ii) Starting from the formula for energy of an electron in the nth orbit of hydrogen atom, derive the formula for the wavelengths of Lyman and Balmer series spectral lines.
iii) What is the speed of a proton having de Broglie wavelength of 0.08 Å?
Section - D
Attempt any One. [1 x 4 = 4 M]
i) What is logic gate? Write down the truth table and Boolean expression for ‘NAND’ gate.What are the uses of logic gates? Why is a NOT gate known as an inverter?
ii) Show that the frequency of the first line in Lyman series is equal to the difference
between the limiting frequencies of Lyman and Balmer series.
